the properties of led lighting

APPLICATION NOTE THE PROPERTIES OF LED LIGHTING

Stefan Fassbinder

March 2013

ECI Publication No Cu0177

Available from www.leonardo-energy.org/node/156891

Publication No Cu0177

Issue Date: March 2013

Page i

Document Issue Control Sheet

Document Title: Application Note – The Properties of LED Lighting

Publication No: Cu0177

Issue: 01

Release: March 2013

Author(s): Stefan Fassbinder

Reviewer(s): Bruno De Wachter

Document History

Issue Date Purpose

1 March

2013

Initial publication in the framework of the Good Practice Guide

2

3

Disclaimer

While this publication has been prepared with care, European Copper Institute and other contributors provide

no warranty with regards to the content and shall not be liable for any direct, incidental or consequential

damages that may result from the use of the information or the data contained.

Copyright© European Copper Institute.

Reproduction is authorised providing the material is unabridged and the source is acknowledged.



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CONTENTS

Summary ........................................................................................................................................................ 1

Introduction .................................................................................................................................................... 2

A little physics to begin with ........................................................................................................................... 4

Different principles for controlling current ..................................................................................................... 6

Current rectified, but not limited ........................................................................................................................... 6

Current limited, but not rectified ........................................................................................................................... 7

With stabilized power and secondary HF pulse ...................................................................................................... 8

With stabilized power and primary HF pulse.......................................................................................................... 9

“Without anything” in special cases ..................................................................................................................... 11

Low voltage and alternating current .................................................................................................................... 11

Low voltage and direct current............................................................................................................................. 11

Mains alternating current ..................................................................................................................................... 11

General properties ........................................................................................................................................ 11

A variety of colours ....................................................................................................................................... 13

Greater efficiency ......................................................................................................................................... 15

First way of cheating: it burns whiter than white! ............................................................................................... 15

Second way of cheating: day vision and night vision ........................................................................................... 17

Third way of cheating: colour rendering index ..................................................................................................... 17

Fourth way of cheating: Let us just measure something else .............................................................................. 20

No need to cheat with LEDs.................................................................................................................................. 21

Greater efficiency? ....................................................................................................................................... 21

Value for money, reasonably priced or inexpensive? .......................................................................................... 21

The mysteries of pricing ....................................................................................................................................... 23

Service life .................................................................................................................................................... 25

Market mechanisms with new products .............................................................................................................. 25

The bluff factor in service life ............................................................................................................................... 26

Service life of drivers ............................................................................................................................................ 26

Market obstacles .......................................................................................................................................... 27

Obstacle 1: Power ................................................................................................................................................. 27

Obstacle 2: Colour ................................................................................................................................................ 28

LED tubes ...................................................................................................................................................... 30

How to yield energy savings with LED tubes ........................................................................................................ 31

How to increase the service life with LED tubes ................................................................................................... 35



Page iii

LEDs for street lighting ......................................................................................................................................... 36

Conclusion: outlook ...................................................................................................................................... 37

References .................................................................................................................................................... 40



Page 1

SUMMARY Incandescent lamps are cheap but tend to have short lifetimes. The light emitted by incandescent sources is

perceived as particularly pleasant because these hot radiators generate a continuous (or full) emission

spectrum. Nevertheless, as hot radiators they waste much of the electrical energy supplied to them.

Compact fluorescent lamps (CFLs) are actually among the least compact of all the various lamps commercially

available at present. Although CFLs are certainly energy efficient, replacing an incandescent light bulb with a

CFL is not just a matter of screwing out one lamp and screwing in the other. While the CFL thread fits the lamp

holder socket, the lamp does not always suit the luminaire—and it is not uncommon for users to reject the

energy-saving CFL on purely aesthetic grounds.

Figure 1—Why is this lamp called “compact”? To point directly at its weakest point…

Then suddenly in a world concerned about energy prices, everyone seems to be speaking of LED lamps as

being the most energy efficient device available and outperforming fluorescent lighting by about as much as

the latter once exceeded incandescent lighting. This is not actually the case. Today's LED lamps are not yet

quite as efficient as fluorescent ones, their current potential use is limited, and their values and ratings are

often being "tuned". It is a pity that incomplete and sometimes even misleading data became one of the most

distinctive aspects in the promotion of LEDs. The facts are that LEDs do provide some features and

characteristics which differ so much from all other lighting techniques that their real potential has yet to be

discovered. This introductory Application Note aims at explaining what LEDs can do and what they cannot,

how "tuning" in advertisements and even customer data sheets works, and where the real potentials lie.



Page 2

INTRODUCTION Incandescent light bulbs are cheap, but short-lived. They produce a particularly pleasant warm light that forms

a continuous spectrum. This means they use a lot of energy, which explains why they have been banned in the

EU.

Compact fluorescent lamps (CFLs) are the last light source to qualify for this name (Figure 2). Although they are

very energy efficient, they are bulky and therefore seldom an appropriate replacement for existing

incandescent bulbs. Even if the thread fits, the appearance of the CFL once fitted into the light fixture is often

enough to discourage potential consumers. Figure 1 illustrates that an incandescent light bulb at one point

used approximately €45 in electricity every year.

Compact fluorescent lamps are criticized both fairly and unfairly. Some consumers complain that the light

emitted by CFLs is cold. In fact, there are now plenty of warm tone lights on the market. The light produced by

a CFL used in an objectively measurable cold environment is often not as bright as desired. It is also not good

to switch CFLs on and off frequently. Incandescent light bulbs are useful in headlights and spotlights and are

easy to dim. CFLs on the other hand can only be dimmed in certain applications and then at extra cost. With a

minimum angle of radiation of around 120°, CFLs are spotlights in name only. Both CFLs and incandescent light

bulbs become less energy efficient when dimmed.

Figure 2—Left, a mains voltage halogen bulb is too hot, an energy guzzler, and has a short life. The

(theoretically) compatible CFL on the right is too bulky (see Figure 22) and hard to focus. Does the LED bulb (in

centre) now provide the solution?

There is a need for a light source that:

Can be switched on and off frequently without a negative impact on its service life

Provides full output instantly

Can be dimmed to zero at minimal expense

Is equally efficient when dimmed as when on full power

Is capable of providing a wide or pinpointed light depending on the design

Has a long service life



Page 3

And, on top of that, is affordable

Such lights are already available in principle. However, what is considered to be affordable is a matter of

opinion. When a source of light is available which costs ten times more than a halogen bulb but lasts twenty

times longer and only uses a quarter of the energy, it should not be considered more expensive.

Light emitting diodes (LEDs) have been in wide use for over four decades as indicator lights. Then major

developments occurred over a relatively short period and LEDs became much brighter and useful for a wide

spectrum of lighting applications. The properties of LED lighting are highlighted below.



Page 4

A LITTLE PHYSICS TO BEGIN WITH As their name suggests, LEDs are semi-conductor diodes. To produce light, they must be forward biased.

Although they would produce light the other way round, the light would be short-lived and could also produce

a smell. The cut-off voltage of an LED is relatively low, as it is not designed to be used as a rectifier diode. As

with all diodes, an LED has exponential characteristics in forward bias. This means that there is an exponential

relationship between voltage and current instead of the linear (proportional) relationship of Ohm’s Law.

Therefore, the diode current ID is dependent on the voltage UD and is calculated as follows:

1T

D

nU

U

SD eII

[1]

Where:

n is the emission coefficient, effectively a correction factor for the individual diode

is the temperature voltage

k = 1.38*10-23

J/K is the Boltzmann constant

q = 1.6*10-19

is the elementary load (the load of an electron)

T is the absolute temperature of the barrier layer at the time of measurement [K]

IS is the saturation cut-off current of a diode, which—virtually irrespective of the current—also flows

in the cut-off direction provided that the cut-off voltage is not exceeded. For a germanium diode, it is

in the order of 100 nA; for a silicon diode it is around 10 pA. That is a ratio of 1:10,000, even if the

absolute values in both cases are very small. This value is very important for calculating the behaviour

of the diode in forward bias (Figure 3).

Figure 3—Characteristics of a single (large) LED for lighting.

0 mW

40 mW

80 mW

120 mW

160 mW

200 mW

240 mW

280 mW

320 mW

0 mA

10 mA

20 mA

30 mA

40 mA

50 mA

60 mA

70 mA

80 mA

1.5 V 2.0 V 2.5 V 3.0 V 3.5 V 4.0 V

P→

I→

U →

Basic characteristic of an LED

ID theor (cold)

ID theor (warm)

ID meas

PD theor (cold)

PD theor (warm)

PD meas



Page 5

The formula also shows that the temperature is very important, as it is part of the exponent. Temperature

changes with the current, however. Fortunately, temperature is in the denominator of the exponent, which

prevents the current from rising even more sharply with rising voltage than it already does. This can be

demonstrated by measuring the behaviour of an LED for solar-powered lighting. The thin lines in Figure 3 show

the theoretical curves calculated for cold and warm states, based on the assumption that there is negligible

warming of the diode at 0.8 mA and that it rises to 53 K at 80 mA. The ambient temperature was 19 °C or

rather, as indicated in the formula, 292 K. Applying a correction factor (or emission coefficient) of n = 5.7, the

curves for current and power (in the range from 0.8 mA to 80 mA) lie, as expected, between the two

corresponding pairs of curves of cold and warm states. Therefore, the correction factor provides a realistic

representation of the diode used as an example.

The thick lines in Figure 4 are also important, as they illustrate the practical behaviour under the influence of

unavoidable heat caused by current.



Page 6

DIFFERENT PRINCIPLES FOR CONTROLLING CURRENT Within the range used in contemporary applications, very small changes in voltage lead to extremely large

changes in current, and equally so in power. This means that current has to be limited in some manner. The

solution adopted in a 12 V LED spotlight is easily measured with a suitable measurement device. Such 12 V LED

spotlights have been available for several years as a compatible replacement for 12 V halogen bulbs.

CURRENT RECTIFIED, BUT NOT LIMITED

As in many small electronic devices, the simplest solution is to fit a bridge rectifier at the inlet, which feeds into

a smoothing capacitor and then to the LED or a series of connected LEDs with the appropriate resistance. In

general, it is not possible to use LEDs or diodes directly in parallel, since the sharp increases in characteristic

curves in the forward bias caused by minor manufacturing tolerances will lead to very large differences in

individual currents. The power input when changing the input voltage (Figure 4) and consideration of the curve

form of the input voltage for an AC power supply current—low voltage, nominal voltage and overvoltage

(Figure 5)—indicate the use of this technique. This solution has the advantage that the LED current, although

not constant, still flows without interruption if a sufficiently large smoothing capacitor is connected between

the rectifier and the resistance. This ensures a more continuous load to the LED than would be the case

without the capacitor and attenuates 100 Hz flickering of the light – the more, the greater the smoothing

capacitance is.

Figure 4—Simple Megaman 12 V 1.7 W LED for DC and AC power supplies…

0.0 VA

0.5 VA

1.0 VA

1.5 VA

2.0 VA

2.5 VA

3.0 VA

3.5 VA

4.0 VA

0 mA

75 mA

150 mA

225 mA

300 mA

6 V 7 V 8 V 9 V 10 V 11 V 12 V 13 V 14 V

P;

Q;

S →

I→

U →

LED lamp 12 V 1.7 W warm white(Megaman)

I =

I ≈

P =

P ≈

S ≈

Q ≈



Page 7

Figure 5—...and its input current curves for 10 V, 12 V and 14 V AC.

CURRENT LIMITED, BUT NOT RECTIFIED

Somewhat more elegant is the replacement of the resistor by means of a transistor with a corresponding

control circuit forming a current limiter (linear regulator). This allows the current to pass through virtually

unhindered in the event of low voltage, but limits it to set maximum values at nominal voltage and especially

at overvoltage (Figure 7). Both solutions brake (so to speak) the surplus voltage, but nothing more than that.

This is not enough to keep the output constant (Figure 6). Additional resistive losses are only avoided at low

voltage, because in that case there is no current limitation, so the supply voltage lies practically directly across

the LEDs. At nominal voltage however, there are additional resistive losses, and even more so at overvoltage. It

apparently has been decided to omit the smoothing capacitor; otherwise, it would not be possible to see the

capping of current peaks so clearly on the input side of the LED.

Figure 6—Osram 12 V 1.25 W LED using DC and AC power supplies...

0.0 VA

0.5 VA

1.0 VA

1.5 VA

2.0 VA

2.5 VA

0 mA

50 mA

100 mA

150 mA

200 mA

6 V 7 V 8 V 9 V 10 V 11 V 12 V 13 V 14 V

P;

Q;

S →

I→

U →

LED lamp 12 V 1.25 W white(Osram)

I =

I ≈

P =

P ≈

S ≈

Q ≈



Page 8

Figure 7—…and its input current curves for 10 V, 12 V and 14 V AC.

There is an intermittency in the LED current that cuts down the power rating even more and generates a 100

Hz strobe light that is much more noticeable than with incandescent bulbs and fluorescent lamps. This is

because filaments and fluorescent lights emit an afterglow while LEDs do not. The development of a so-called

optical LAN has already been considered to convey data, using an LED light source and superimposing it to an

invisible high frequency flickering [2]. This would be impossible with incandescent and fluorescent lamps.

WITH STABILIZED POWER AND SECONDARY HF PULSE

More expensive, more sensitive, but also more energy efficient is an electronic, high frequency pulse solution,

especially for any form of islanded use with limited availability of electrical energy, as is the case for solar

powered traffic signs, garden lights, and the like. This is where LEDs have been most widely used until now; in

devices like torches and bicycles, and as an alternative to incandescent light bulbs. Where popular halogen

spotlights can be replaced by LED lights, they are generally designed to be used with both direct and

alternating current. This does not involve any major technical modifications, since there is generally no

problem in allowing the direct current to flow through another bridge rectifier situated on its path.

Nevertheless, at the entry to the current circuit, there is still the usual rectifier circuit with capacitive

smoothing, as can be seen from the current curve (Figure 9). As with the CFL, a high frequency Pulse Width

Modulator (PWM) comes after this to make it possible to keep the power input constant. This can be seen in

the TRMS value of the input current that gets smaller instead of larger with higher voltage (Figure 8).



Page 9

Figure 8—Behaviour of Conrad 12 V 3 W LED …

Figure 9—… and its input current curves for 10 V, 12 V, and 14 V AC.

WITH STABILIZED POWER AND PRIMARY HF PULSE

Currently, the fourth development displays a high frequency pulse at the input (Figure 11). However, no

attempt was made to reproduce the current sinus curve, as is done with electronic ballasts for fluorescent

lamps in the range above 25 W. Otherwise, this would not meet the statutory requirements [3]. Instead, the

current is converted into a rectangular high frequency shape with a peak value of ≈1 A. The average value of

the current is adapted by a PWM. This also occurs when used with direct current to keep the power constant

when the voltage fluctuates. The TRMS current can therefore deviate from the arithmetic mean value. When

multiplied by the actual voltage, it gives the apparent power, not necessarily the active power (Figure 10)

when working with direct current, since the direct current pulsates and is not a pure direct current. Here, we

define direct current to mean anything that never changes direction; the term does not require constant

amplitude of current. While the 7 W power intake already had to be considered a very high value for the LED

0 VA

1 VA

2 VA

3 VA

4 VA

5 VA

0 lm

150 lm

300 lm

450 lm

600 lm

6 V 7 V 8 V 9 V 10 V 11 V 12 V 13 V 14 V

P;

Q;

S →

I→

U →

LED lamp12 V 3 W

warm white(Conrad)

I =

I ≈

P =

P ≈

S ≈

Q ≈



Page 10

light tested, this still represents a very small load. Therefore, the current harmonics were not limited by any

additional measures. The applicable limit values are extremely generous for lamps and luminaires up to 25 W

[3], which is why no type of filtering or similar conditioning was required. We question whether electro-

magnetic compatibility (EMC) is still achieved in the higher frequency range, since our top quality measuring

equipment was unable to give a good oscilloscope reading (Figure 11 top left). This was apparently due to

interference from the sample being tested. Even earthing and a distance of 1.5 m could not alter this. Adding

to this, this lamp had entered the market in order to solve the problem by simulating the electrical

characteristics of a low voltage halogen light, or in other words, simulating the properties of an ohmic load [4].

Figure 10—Behaviour of Philips 12 V 7 W LED with expensive electronics…

Figure 11—…and its input current curves for 10 V, 12 V, and 14 V AC.

0.0 VA

1.5 VA

3.0 VA

4.5 VA

6.0 VA

7.5 VA

9.0 VA

10.5 VA

12.0 VA

13.5 VA

0 mA

200 mA

400 mA

600 mA

800 mA

1000 mA

1200 mA

6 V 7 V 8 V 9 V 10 V 11 V 12 V 13 V 14 VP

; Q

; S

→

I→

U →

LED lamp 12 V 7 W (Philips)

I = I ≈

P = P ≈

S = S ≈

Q = Q ≈



Page 11

“WITHOUT ANYTHING” IN SPECIAL CASES

In some cases, there is no control electronicsat all. The energy savings effect is achieved by eliminating the

corresponding losses. Energy is still far too cheap, so cost savings still offer a limited incentive to save energy.

Nevertheless, when other factors greatly restrict the availability of electrical energy, for example, when human

beings have to work hard to create energy, or it has to be generated chemically in batteries, or chemically

stored in expensive, heavy rechargeable batteries, suddenly there are all sorts of “new ways available for

potential energy savings.”

LOW VOLTAGE AND ALTERNATING CURRENT

In the bicycle light and its dynamo mentioned above, there is—in the strictest physical sense—a current source

instead of a voltage source. The short circuit current is marginally higher than the normal operating current,

but the open circuit voltage is much higher than the normal operating current. This increases the faster you go,

as the open circuit voltage increases in proportion to the rotational speed. However, the same thing applies for

frequency and as the short circuit current is limited mainly by the internal inductive reactance of the dynamo,

the short circuit current barely changes with the rotational speed. These are ideal operating conditions for a

direct connection of a suitable LED with the short circuit current of the dynamo, if used anti-parallel in duo.

The voltage is adjusted accordingly. However, with today’s gearless hub dynamos, there is low frequency

flickering when the bicycle is pushed. Rectification and buffering with a rechargeable battery improves the

situation, as does the use of a smoothing capacitor.

LOW VOLTAGE AND DIRECT CURRENT

In some circumstances, a suitable LED can also be connected directly to a source of direct current. Fully

charged accumulators and batteries have an operating voltage which lies above the nominal value; when they

come close to discharge, it lies somewhere below the nominal value. The exponential characteristics (Figure 3)

reinforces this behaviour and provides plenty of light if there is enough current, but starts to make drastic

savings if current is scarce. Old incandescent light bulbs, which were not very energy efficient in any case,

became even less so when the voltage was too low, making lighting very dim.

MAINS ALTERNATING CURRENT

Light strings in which a sufficient number of LEDs are connected in series and then directly to the mains

supply—using a protective resistor, or even without one—are somewhat rare. If two LEDs are connected anti-

parallel, the rectifier can even be eliminated in some cases. The energy efficiency is excellent, because there is

no power lost in any upstream element. However, the individual little lights are flickering visibly, as each one

of them is only powered by one semi-wave.

GENERAL PROPERTIES We might wonder why LED lamps, even with the rather small nominal output of 1 W, are made up out of a lot

of small LEDs, while power LEDs are available for a similar price in which a single element provides an output

of several watts (Figure 12). This power LED might even be just as small as a single LED out of a multiple LED

light source. Some retailers already offer single LEDs up to a power of 18 W [5]. However, individual LEDs

become less efficient the larger they are, and the problem of heat dissipation becomes more serious with

power LEDs, since they have a high concentration of output on what remains a very small surface. In multiple

LED modules, several semiconductors are interconnected in a cluster. This is how LED modules for virtually any

nominal voltage can be built, depending on how many diodes that are connected in series. There are even

modules that can be connected directly to the mains supply.



Page 12

Figure 12—Different principles: An LED with 3 W nominal output or 18 LEDs combined to make up 1 W nominal

output.

Figure 13—Behaviour of an LED light with under voltage.



Page 13

Whether the LEDs of a light source are interconnected in groups can be determined by decreasing the voltage

level. If they are interconnected in groups, they do not all darken to the same extent. With only 7 V DC applied

to a 12 V multi-LED lamp, not more than two LEDs light up. These two, however, are still remarkably bright

(Figure 13).

One particular advantage of the 12 V LED bulbs is that they can be used to replace existing halogen spotlights

without modification. However, they can only be used with a conventional halogen light transformer. They

cannot be used with electronic halogen light transformers. The manufacturers give no reason for this, but it

must have something to do with the electronic transformers rather than with the LEDs, since these

transformers cease to work or make the connected lights flicker when the load drops too low below the

nominal value [4].

Only the models with primary pulse can be used for mains voltage lights, since the voltage must first be

decreased. There is no scope of application for modules that can be used directly with mains voltage, given

their low output, since too few elements can be connected in a row. This should be reserved for street lighting.

There would need to be a way of coping with the flickering, so electronics would be required again.

Alternatively, perhaps three-phase AC LEDs are the solution?

A VARIETY OF COLOURS LED lights are best suited for the rear lights and indicators on motor vehicles. This is due to the fact that the

desired colour can be produced directly without producing a continuous spectrum with incandescent light

bulbs, which are already inefficient as such, and from which you then have to filter out all the other colours.

LEDs as a single source of light also do not react badly to frequent on/off switching. It is remarkable that cars

are made in which the 5 W incandescent light bulbs in rear lights have been replaced by red LEDs, yet the

indicators and brake lights still have 21 W incandescent light bulbs. We are also still waiting for LED headlights.

However, it should be noted that the use of LEDs in motor vehicles is never justified simply for energy

efficiency reasons, due to the low operating times of those lights. The reduced maintenance is not an

advantage either, since the incandescent light bulbs used in motor vehicles have improved so much that most

of them already last longer than the vehicle. Also, a privately owned car is only used around 200 hours

annually and is not driven constantly with the lights on. As with most other exterior components for cars, it is

primarily a question of look or appearance. Since LED lights are still quite expensive, they usually appear only

on the more expensive cars.

Once again, it is bicycles with only 3 W of available electrical output on board which benefit most from LEDs.

These offer increased safety, more light, and fewer failures. The somewhat penetrating bluish colour of cool

white light makes LEDs more energy efficient compared to warm white and perhaps most importantly, also

more visible.



Page 14

Figure 14—LED replacement for battery torches and possibly for …

Unfortunately, it has only been possible to use LEDs to replace E10 rear lights on bicycles up to now. No white

LEDs with sufficiently large output could be found at Light & Building 2012. Since then, it has been possible to

track down only a single example (Figure 14). It had half the output—and so still roughly twice the

illumination—of an old bicycle incandescent light bulb, but this little light is still not authorized for use on a

bicycle (Figure 17).

Figure 15—… bicycles..



Page 15

The most obvious advantages of LEDs are in decorative lighting. Lighting scenarios are available with changing

colours using a multitude of small, scattered points of light. As explained above, while this is much better than

using small low voltage incandescent light bulbs, it does involve an area in which there is no further need to

talk of potential improvement, since great luminous fluxes are seldom used in decorative lighting. Too bright

would no longer be “cozy”.

LED spotlights are being used more and more for stage lighting, despite the fact that they cost more. This is

primarily because they can be used very effectively to create all sorts of colour changes. Combining LEDs of

different colours in a spotlight reduces the required amount of connected power to something like a tenth of

the values required for incandescent light bulbs. LEDs are easy to direct, they switch on and off, and can be

dimmed up or down immediately. This makes them ideal for replacing incandescent light bulbs which were

previously the only ones that could meet these requirements. They did however require all sorts of thermal

management. Replacing mechanically moving colour filters with separate electrical controls for different

colours increases reliability. It also eliminates frightening audiences and performers since incandescent lamp

failures are often accompanied by a loud bang in the middle of a performance. When LEDs die, they do so

slowly and softly and it can be calculated to never to occur during the few hours in which they are being used

on stage. Ideal is a word which is often overused, but using this light source for this purpose is indeed virtually

ideal.

GREATER EFFICIENCY LEDs are expected to have a great future. This is due to the whole range of benefits they offer (see

introduction). The most important one is energy efficiency. The efficiencies of technical equipment and

processes are usually shown as a percentage ratio of output by input power. However, this does not apply to

lights, since the human eye is more or less sensitive to different colours with regard to perceived brightness.

The unit of light output for a light source is already calibrated to the sensitivity of a normal eye. The efficiency

of lamps and luminaires is shown in lumens per watt. This is the only suitable way of indicating which technical

device produces the greatest perceived brightness per electrical input. Even so, a great deal of background

knowledge is still required to be able to interpret this measurement correctly.

FIRST WAY OF CHEATING: IT BURNS WHITER THAN WHITE!

It is theoretically possible to achieve a light output of exactly 683 lumens per watt [lm/W]. However, this is for

a monochromatic green light with a wavelength of 555 nm, to which the human eye is the most sensitive (at

least in strong lighting). So the greenest light source is green indeed. Whether we want to use it to light our

streets, squares, halls, supermarkets, offices, and living rooms, is quite another matter. A theoretical maximum

of 182 lm/W is given for white light, or light that we perceive as white, if all the colours with wavelengths from

380 nm to 780 nm are mixed in the right proportions. A calculation [7] with a theoretically assumed objective

white light source in which all colours from 380 nm to 780 nm are represented with the same physically

measurable intensity of light, renders such result, in case the electrical input is converted for 100% to light.

However, as we know from many experiments investigating the perception of light by the human eye, an

entirely objective continuous spectrum is perceived to have a significantly weaker light intensity. For example,

a red or blue light of 1 W is perceived as being much darker than a green light of the same power. When

converting watts to lumens, the continuous spectrum of white light is thus given a much lower value than a

monochromatic green light with 555 nm wavelength.

In reality, no light exists which has such a continuous straight spectrum. Even the incandescent light bulb

which, contrary to other lights, falls continuously (from red to blue), does not have the same output for each

wavelength. One light may emit a lot of light in the green spectrum and another may emit more light in



Page 16

spectra to which humans are less sensitive, and yet both lights might be perceived as white. The first of those

two white lights will consequently have a larger possible light output than the second. Even if the first one has

a poorer objective, physical level of energy efficiency (light output divided by electrical power input), it still can

provide more light per electrical power input (lumens per watt). Black lights designed to produce invisible

ultraviolet light are an extreme example of this. Such a light may have a high physical level of efficiency in

percentage (UV light in watts divided by electrical power input in watts), but their light output in lumens per

watt is zero in ideal circumstances – and close to zero in reality, as it unavoidably creates some visible light as

waste.

Note that “black light” is something similar to “round squares”. Strictly spoken, “light” can only mean visible

electro-magnetic radiation. To be correct, UV and IR “light” would need to be called ultraviolet and infrared

radiation.

Figure 16—Spectral distribution for a sample LED [9] (Vλ: Standard sensitivity of the human eye—a peak

exactly where there should be a peak for the brightness of an LED).

A calculation was made to compare the spectrum measured for a typical LED (Figure 16) with that of an

appropriate sample. The result: if this LED had a 100% energy efficiency level, that is, if it were to produce only

light and no heat, it would provide 302.75 lm/W (instead of 182 lm/W if it were to provide a theoretical ideal

white). It would not need to be cooled. Dream on. The first draft standards for evaluating LED light foresee (yet

again) two types of measurements: the same light will look better—not optically, but numerically—if it comes

from an LED rather than from a fluorescent light.

However, LEDs do have an objective advantage over fluorescent lights for producing white light. Fluorescent

lights produce a pure UV beam, which has to be converted into visible light using a conversion or fluorescent

layer. This process incurs considerable losses.

LEDs, however, emit a blue light. Only part of this blue light has to be converted, and the conversion does not

need to take such a big step in the frequency spectrum (for example, only from blue to yellow) (Figure 16 to

Figure 21) [10]. In the past, sometimes more blue light was used directly than required for a good white

mixture. This is what gave the bluish tone to older, less expensive LED lights.



Page 17

SECOND WAY OF CHEATING: DAY VISION AND NIGHT VISION

At night, all cats look grey. Nevertheless, the sensitivity of the human eye goes from green to blue. Although

we can no longer see colours, we perceive a blue cat to be lighter grey than a red one, with the same physical

intensity of light.

At night, once the eye has become accustomed to the dark, sensitivity is the highest for green light, even more

so than in daylight. With 1,699 lm/W, the light output of a blue-green light source would be 507 nm, so

achieving 100% energy efficiency. We could take this value as the benchmark, as the human eye is apparently

capable of developing such sensitivity. But this would also mean that the observed/measured source of light

would have left the surroundings in utter darkness and would therefore ultimately have failed its purpose.

Anyone attempting to improve the efficiency figures for LEDs in this way is doing it a disservice, as this implies

that the light is extremely weak and thus not suited for night use.

THIRD WAY OF CHEATING: COLOUR RENDERING INDEX

The colour rendering index is used to quantify the quality of light. How the index is derived and defined is

complicated and goes beyond the scope of what is being discussed here.

However, you would expect that if a light has a colour rendering index of Ra = 100, its colour rending would be

ideal. This is not necessarily the case, because the colour rendering index is also a relative value. For colour

temperatures under 5,000 K, it refers to the specified colour temperature of the light in question; upwards of

5,000 K, it refers to daylight. Daylight is not sunlight and does not have a continuous spectrum. The sun is a

blackbody radiator with a surface temperature of approximately 6,000 K. This surface temperature is also its

colour temperature. Each light source with a continuous spectrum that has the same temperature glows

equally bright and with equal distribution of colours. It is only because of this that it is possible to use colour

temperature as a measure to compare various sources of light. If the colour temperature is around 6,000 K, it

is called daylight white. However, in the atmosphere, various colours of the sun’s spectrum are broken up,

scattered, and absorbed. As a result, daylight on the earth’s surface has a discontinuous spectrum. On top of

that, this spectrum fluctuates greatly according to the time of the day. This means that the term a typical

daylight spectrum has to be specified more precisely. This also means that a light source which can reproduce

this discontinuous spectrum exactly, achieves the best colour rendering; whereas a light source which has a

totally flat distribution of wavelengths does not. This leaves an opportunity for cheating or at least

misrepresentation to a certain extent. This is not only true for LEDs, but for any light source for which the

spectral distribution may be influenced by its design and manufacture. This opportunity is being widely

exploited.



Page 18

Figure 17—A demonstration which shows…

Figure 18—…how much blue light you can get from a small 9 V battery…



Page 19

Figure 19—…but also how a fluorescent layer can create many shades of white light from it…

Figure 20—…either using transillumination…



Page 20

Figure 21—…or epi-illumination.

FOURTH WAY OF CHEATING: LET US JUST MEASURE SOMETHING ELSE

In order to conceal that LEDs were not (yet) the brightest and best, brightness at the start was often given, for

example, as 240 lux for a 1.5 W light. That is meaningless since lux, which is another word or a synonym in

Latin for light, is only the unit for luminance. Therefore, if the light can be focused more sharply, on around

half the angle of exit, the same amount of light hits a quarter of the surface. So the numerical value becomes



Page 21

four times better without the light flux or level of efficiency (light output) of the light source in question having

become any greater. By halving the distance to the light source, the value quadruples, as absolutely nothing

was specified about the distance to which the value referred. If all goes well, all that the consumer remembers

is the numerical value and he then thinks that this is the light flux in lumens or the efficiency in lumens per

watt. Obviously, measuring brightness in lumens [1 lx = 1 lm/m²] over the surface of the beam is important for

describing the properties of an entire lighting system, but it says about just as much about the light output or

energy efficiency of a single source of light as the gear ratio of a car does about engine performance.

NO NEED TO CHEAT WITH LEDS

You have to be careful about what is being compared with what when you hear about the excellent efficiency

of LEDs. Replacing a halogen spotlight with an LED spotlight represents tremendous progress. However, it

cannot be repeated often enough: halogen lights are incandescent lights and are only marginally more

efficient than incandescent light bulbs. Clear halogen light bulbs are in class D of the EU classification scheme

for domestic appliances (going from A to G), and frosted halogen bulbs are even lower down in class E.

Comparing LEDs with fluorescent lights is another story. Laboratory measurements [7] of prototype industrial

LED systems with converter show results of around 100 lm/W. Fluorescent lights show similar results and are

already in commercial use.

Bulbs of less than 4 Watt are noticeably missing from the requirement to label the efficiency class. This is a

loophole which can be exploited for LED light sources which, as explained, use light from a lot of small point

sources. On top of that, a large part of residential LEDs are under 4 Watts. This means that there is no

requirement to demonstrate the energy efficiency for the majority of LED lights for residential use that are

currently available on the market.

GREATER EFFICIENCY? Smart metering is a nice catchphrase which you need to use as often as possible if you want to join in and be

part of the discussion. In reality, energy consumption is still like those vehicles owned by a company filling up

at a petrol station which does not show either the litre price of fuel, the amount of fuel taken, or the cost of

fuel taken. At the end of the year, the company simply gets an invoice showing the total fuel consumption and

total cost. No one has any idea which vehicle filled up when with fuel and how much it used, or about times

when fuel was very expensive and times when it was not quite so expensive. No company would accept this

for other products, but this is normal practice for electricity, gas, and water for both commercial and domestic

consumption. It is only because of this mechanism that it is possible to sell a vehicle which uses around 3 litres

of fuel an hour when idle because the motor cannot be switched off, with the argument that it saves a few

hundred euros for a starter and battery.

VALUE FOR MONEY, REASONABLY PRICED OR INEXPENSIVE?

Is such a state of affairs intolerable? For cars, it is. However, for electricity it is quite normal. As is the case with

many other electronic devices, a cheap but by no means cost efficient or good value for money LED light

(Figure 22) is left to run idle when the light is switched off. If you do not like that, all you can do is pull the plug.

You then have to look under the sofa to find the plug to turn it on again. Idle electric power consumption (not

only as compared with cars where it converts to around 3 l/h) is exorbitantly high and could have been

reduced by around 60% if about 50 cents more had been spent on grain-oriented steel when designing the

mains transformer, nothing more. The investment would be paid back in six months. The consumer would be

unlikely to notice this, so would not have paid for it, as the manufacturers will protest, regrettably with reason.

The relatively small amount in relation to the overall electricity bill would be lost in the background noise. It is

relatively annoying to say that everything is relative, as the waste is very high in relation to the energy used. If



Page 22

the net power is deduced from the gross power, it can be seen that the total power lost with the power supply

unit is only slightly more than the power lost on standby. If this light is on for around 1,400 hours a year, it is

no more efficient than the incandescent bulb it is intended to replace (Figure 22), and so saves nothing. If it is

used less, it even costs more. In constant use, the LED would save around 100 kWh a year, but constant use is

rather unlikely for a reading light. The main cause does not lie with the LEDs themselves. They still achieve a

good level of efficiency, even for small output ranges, where other light sources are not as successful.

Figure 22: Value for money? Reasonably priced? Definitely not cheap—and by no means economical…

Figure 23: …if the light still uses more than half as much electricity with the light is switched off.

0 €/a

2 €/a

4 €/a

6 €/a

8 €/a

10 €/a

12 €/a

0 h/a 1000 h/a 2000 h/a 3000 h/a 4000 h/a

Ele

ctr

icit

y c

os

ts →

Annual operating time →

Energy costs of an LED luminaire with plug-integrated power unit versus incandescent lamp

LED reading light 1.8 W

Power intake



Page 23

THE MYSTERIES OF PRICING

We have wondered already why an output of only 1.8 W is split between no less than 18 LEDs (Figure 22,

Figure 25) when you can buy single LEDS with nominal outputs of up to 18 W [5]. It is also surprising that a

complete light with 18 LEDs, the light fixture, power supply, plus all the mechanics and wiring can be sold for

around only €10 (see Figure 22).

Figure 24: Overview of a selection of CFL and LED bulbs available on the market for domestic use, with a few

incandescent light bulbs for comparison

0lm/W 25lm/W 50lm/W 75lm/W

0lm 1000lm 2000lm 3000lm

CFL Megaman MM10102, 3 W



CFL Osram Dulux Pro Micro Twist, 7 W



CFL Osram Dulux Intelligent Factory, 10 W












CFL Philips MASTER PL1CT, 27 W


CFL Philips MASTER PL1CT, 33 W


LED Osram Parathom Classic A, 2 W

LED Osram Parathom Classic Globe, 3 W

LED Philips 8718291195641, 4 W

LED Megaman MM21010, 5 W

LED Philips MASTER MV 25D, 5.5 W


LED Megaman R7s MM49002, 7 W


LED Philips 8718291192985, 9.5 W

LED Osram Parathom Classic Globe, 10.5 W

LED Megaman MM21016, 11 W


LED Philips 872790091838000, 12.5 W

LED Philips MASTER Bulb E27 MW, 17 W

LED Megaman MODUL MM59013, 20 W

LED Megaman MODUL MM59023, 30 W

General purpose incandescent lamp, 8 W



»Linestra« incandescent lighting tube, 35 W









η →

Φ →

PN→

Light outputs and efficaciesof various lamps

Φ

η



Page 24

The technique of using around 18 individual LEDs to achieve a rather small source of light is actually quite old,

given the relatively short history of LEDs, and represents neither value for money, or reasonable prices. It is

simply a cheap way of reusing surplus industrial stock. This is a way of provisionally storing industrial waste in

homes—the individual LEDs that are combined in the light source often exceeded the set tolerances and only

by combining them with other LEDs that exceed the tolerances in the other direction, they can be re-used. As

is often the case, advertising presents this practice as a virtue and rouses the impression—without explicitly

asserting this—that the number of individual LEDs is a performance feature, which seems plausible. However,

the individual LEDs often have different colour drifts, so their colours change to a different extent and in

different directions with age. As when optimizing the right colour of light by mixing different coloured LEDs,

this gives a cone of light with coloured edges. Anyone who works with LEDs knows this or should know it. LEDs

call for a new way of thinking and buying. Surplus stock and very reasonably priced bargains often prove to be

anything but reasonable. Private consumers rarely have access to ”real” LEDs.

As regards the efficiency savings achievable with LEDS, you must pay attention to what is being compared with

what. There is an enormous advantage over incandescent light bulbs, but comparing the LEDs currently

available with CFL is much ado about nothing. This is highlighted in Table 1 and Table 2 or Figure 24,

respectively, regarding products currently available, along with the incandescent light bulbs in Table 3 to make

the comparison complete. It was, however, not possible to show prices for these.

Table 1 – Comparison of selected compact fluorescent lamps.

P Φ η

CFL Megaman MM10102, 3 W 3W 81lm 27lm/W



CFL Osram Dulux Pro Micro Twist, 7 W 7W 400lm 57lm/W



CFL Osram Dulux Intelligent Factory, 10 W 10W 580lm 58lm/W












CFL Philips MASTER PL1CT, 27 W 27W 1800lm 67lm/W


CFL Philips MASTER PL1CT, 33 W 33W 2250lm 68lm/W





CF

L



Page 25

Table 2 – Comparison of selected LED bulbs.

Table 3 – Comparison of selected incandescent light bulbs.

SERVICE LIFE LEDs change with age. Right from the start the luminous flux decreases, or an individual LED in a light can fail

[11]. The speed of these processes is determined mainly by the operating temperature. The warming up of

individual light diodes can be reduced by not exploiting them fully, that is, by operating them below nominal

power. If twice as many LEDs are used than is necessary for a job and they are then loaded to half capacity,

they can be used for much longer without any negative impact on their efficiency, as would be the case with

incandescent light bulbs. Their high price, however, hampers this approach, especially during the market

introduction phase.

MARKET MECHANISMS WITH NEW PRODUCTS

It is obviously disappointing for consumers when they discover that they have to remove one or two zeroes

from the service life specified. There are an increasing number of reports that the 40,000 hours were already

over after three days, but what should manufacturers do? If they would sell a bulb which is supposed to

P Φ η

LED Osram Parathom Classic A, 2 W 2.0W 100lm 50.0lm/W

LED Osram Parathom Classic Globe, 3 W 3.0W 140lm 46.7lm/W

LED Philips 8718291195641, 4 W 4.0W 250lm 62.5lm/W

LED Megaman MM21010, 5 W 5.0W 240lm 48.0lm/W

LED Philips MASTER MV 25D, 5.5 W 5.5W 270lm 49.1lm/W


LED Megaman R7s MM49002, 7 W 7.0W 450lm 64.3lm/W


LED Philips 8718291192985, 9.5 W 9.5W 600lm 63.2lm/W

LED Osram Parathom Classic Globe, 10.5 W 10.5W 470lm 44.8lm/W

LED Megaman MM21016, 11 W 11.0W 810lm 73.6lm/W


LED Philips 872790091838000, 12.5 W 12.5W 806lm 64.5lm/W

LED Philips MASTER Bulb E27 MW, 17 W 17.0W 1055lm 62.1lm/W

LED Megaman MODUL MM59013, 20 W 20.0W 1200lm 60.0lm/W

LED Megaman MODUL MM59023, 30 W 30W 2000lm 67lm/W

LE

D

P Φ η

General purpose incandescent lamp, 8 W 8W 40lm 5.0lm/W



»Linestra« incandescent lighting tube, 35 W 35W 240lm 6.9lm/W









Incan

descen

t la

mp

s



Page 26

replace a cheap €1 incandescent light bulb for €100 instead of €50 and is also twice as big, consumers will

automatically reach for the €49.95 package with the more compact light with the same power output and the

promise of “up to 40,000 hours of service life”. The addition of “up to” is very important in this, as it makes the

information practically meaningless, especially from a legal viewpoint. This is precisely what happened when

CFLs were introduced. There was also a flood of disappointing reports for them too, but the values specified

have been achieved, more or less, in the meantime. It takes a long time to test the service life of a device with

a long life. If you want to achieve faster results, you have to tighten the conditions and then make the

calculations for nominal conditions. The tighter the conditions, the more imprecise the calculation. A purely

theoretical calculation of service life is even more imprecise. If you want to—or rather have to—sell the

product, the values have to be rounded off in the right direction until you get a good result. The early, still very

expensive products launched on the market anger consumers, and scorn and derision are poured on

manufacturers, but is there any other way to do this? A well-designed product still has to mature with

customers, like beta software. CFL had accomplished this even before the ban on incandescent light bulbs.

LEDs with the systematic advantages they offer in relation to competing products, their unique selling points,

will also manage to do this. In fact, they are already managing to do so quite well. Despite all the peripheral

issues, risks and side effects mentioned above, LEDs are experiencing a major breakthrough now, despite the

great price difference with incandescent light bulbs.

THE BLUFF FACTOR IN SERVICE LIFE

General limitations do, however, apply to the specification of service life. In some build-in applications, the

price of the light source itself is several factors lower compared to the cost of changing the source. Saving on

the price here would drive costs upwards. It is recommended to use long life LED bulbs in such cases. This

remains valid when compared with almost every type of incandescent light bulbs. A fluorescent bulb, on the

other hand, is considered to be at the end of its service life when its light flux drops to 94% of the initial value.

So a standard three band light has a service life of only around 15,000 hours. There are no standard

specifications for LEDs yet; so manufacturers or retailers set the end of useful life at 70%, 50%, or even 30%

remaining light flux as they deem fit. This gives values ranging from 40,000 hours to 60,000 hours. A

fluorescent bulb can also achieve this, if it is never switched off or if it is used with an improved magnetic

ballast (IMB) and electronic starter [12], or if special long life bulbs are used (nothing can be said yet about the

combination of both).

There is another trick involving, for example, labelling a tube supplying 4,000 lm with a nominal light flux of

3,000 lm. When it loses 25% of its original light flux, it still has 100% of its nominal light flux and so age

calculations only start from that point. Although this may be acceptable when launching products, there

should be uniform standards later to ensure good order.

SERVICE LIFE OF DRIVERS

The electronic drivers for LEDs are less complicated than Electronic Ballasts (EBs) for fluorescent lights, since

LEDs do not need to pre-glow or be ignited. They simply light up like incandescent light bulbs. That is why they

are not referred to as LED EBs, even if that is what they are. Specialists are quick to raise their eyebrows when

they hear the incredible figures and to exclaim “And the electronics are supposed to last for 40,000 hours too?

And the fan too?”

With regard to fans and high ambient temperatures, LED EBs, especially when they are integrated into the

light, have the advantage of being equipped with a temperature sensor which triggers the LED to operate with

reduced power if the temperature rises too high. In some circumstances, users may not even notice this, as the

LEDs are almost as effective when dimmed. This is in contrast with fluorescent bulbs. They would lose a lot of

light with temperature-dependent dimming while the power loss of the EB would only reduce slightly.



Page 27

MARKET OBSTACLES The reason why halogen light bulbs have become so popular is because they are often described and sold as

spotlights. If we replace halogen spotlights with LED spotlights, we would have exactly the same effect. It

would not cost any more to integrate suitable optics, or space for a reflector, in LEDs. To this extent, this would

be a smooth, even optimal replacement.

OBSTACLE 1: POWER

Unfortunately, LED lights do not yet have the required power for this. A 1.7 W LED could almost replace the

brilliance of a 5 W spotlight, but not a 20 W or 35 W halogen spotlight which is likely to remain in use for a long

time to come. In the meantime, the market will use its own methods to offer a 7 W LED spotlight which gives

roughly as much light as a 35 W halogen spotlight, but unfortunately with a beam which can not only be seen,

but also heard [4]. Or manufacturers will avoid giving details of light flow (in lumens) and will give luminous

intensity (in candela—but without the necessary indication of direction) or luminance (in lux—but without the

necessary indication of distance), where this directed source of light is strongest. This is done in the usually

justified hope that consumers will confuse this. So not much has changed for the time being. But it will change

in the near future. In Figure 24, for example, when comparing Table 1 with Table 2 and then with Table 3, it

becomes clear that:

CFL have been able to catch up with incandescent light bulbs with regard to light output. They could

even replace a 400 W incandescent light bulb.

LEDs have not yet achieved this. The 17 W LED bulb made by Philips looks very similar to an Osram

bulb with the same specifications. It was launched in autumn 2012 as the successor to the 75 W

incandescent light bulbs. Megaman already offer 20 W and 30 W LED lamps.

Contrary to the general perception, even of experts, LEDs are not more efficient than CFLs. Only very

small LEDs under 4 W offer a clear advantage. However, if you take the average efficiency of all the

light sources listed, it is barely 60 lm/W for both Table 1 and Table 2.

What emerges quite clearly, however, is the great advances of both these techniques in relation to

incandescent light bulbs, for which the same comparison gives an average efficiency of only 10 lm/W.

But there is still a lot of vague wording or straight misrepresentation when specifying equivalents,

which type of CFL and which type of LED can replace which type of incandescent light bulb, and the

next highest known nominal output is listed instead of an exact linear projection. Only the 17 W LED

mentioned above is a true replacement for the 75 W domestic incandescent light bulb—if the

information provided by the manufacturers is correct. Neither Osram nor Philips was brave enough to

go for 100 W straight away.

Despite their relatively good level of efficiency, LEDs still clearly give off more than half the electrical input as

heat, not light. If this were not the case, there would not be any noticeable potential left for improvement –

unless someone invented Perpetuum Lumile, a light with over 100% efficiency. To read some of the marketing

and more sensational reports, you might think that this has already been achieved. This raises the question,

what makes eliminating this small loss of heat such a problem and a limiting factor? Why is it such a problem

for LEDs if they emit 4 W out of 7 W as heat, while a halogen light can emit 32 W out of 35 W as heat without a

fan? There are three reasons for this:

An LED is very small, so heat is concentrated on a very small surface and in a very small volume.

As a semi-conductor, it cannot withstand such high temperatures as an incandescent light bulb made

of metal and glass.

An incandescent light bulb can lose most of its heat—somewhere between 50% and 80%—through

radiation, whereas an LED loses virtually no heat, as its surface is very small and its absolute



Page 28

temperature is too low for achieving a high heat radiation (heat radiation increases to the power of

four with the absolute temperature).

That is why the dissipation of heat in LEDs was renamed thermal management. The major limitation of LEDS is

that no one knows how to evacuate heat from this small component.

The large LEDs mentioned above are sold without cooling and it is specified that the bulb manufacturer is

responsible for thermal management. It is also specified that these LEDs must not be used for longer than 5

seconds without it [5]. The recommendation still being discussed at Light & Building 2012 was that there

should be around 4 cm² cooling surface area per watt of nominal output. In street lights, where LEDs like this

are used most, there is sufficient cooling area available (if not, it would not be recommended to use active

cooling with street lights, for reasons of reliability).

OBSTACLE 2: COLOUR

Light diodes by their very nature emit a narrow band of light, which means that it is comprised of only one

colour. If you want to produce white light, you have to mix two colours, or two different LEDs (not necessarily

three, as can still be seen in older textbooks and documents). At the start, two or three of these LEDs were

combined into one unit. The colour rendering was terrible. Nowadays, this method of creating white light for

internal lighting is hardly used, since a way was found to apply a conversion layer to a single blue LED in the

same way as fluorescent light. Light with higher wavelengths, so lower frequencies and less energy per

quantum of light, can be produced by converting the blue light. After initial difficulties, there is now much

greater success in achieving the right mix and the required colour of white. In the cheap products described,

LEDs of different colours are mixed (Figure 25). In proper, professional applications, the conversion layer does

not have to be integrated into the LEDs, but can also be part of the light element. This means that flexible,

various temperatures of colour can be produced from the same blue LED element (Figure 17 to Figure 21).

Some time ago, you would still have described normal white LED lights as light blue (Figure 27) and the warm

white LEDs more as yellow (Figure 26). However, clear progress has also been made. At Light & Building 2010

one British exhibitor was brave enough to shine conventional halogen spotlights and their own LED spotlights

on two rag dolls with the same brightly coloured clothes and to ask visitors to identify which light source was

being used. Around 50% of visitors guessed correctly. So we now have to overcome such pre-conceived

notions, as is always the case after eliminating the teething problems with any new technology.

We do not know how long the lights in Figure 27 have been in use. Maybe the restaurant owner paid a lot of

money for them a long time ago when they were little more than prototypes and they are unfortunately

lasting forever—and continue to confirm pre-conceived notions.



Page 29

Figure 25 – The various colours being used in the LED array in Figure 22 helps to produce white.

Figure 26 – Three CFL as compared with a white LED light (back right) and a warm white LED light (back left).



Page 30

Figure 27 – Entrance area to toilets in a restaurant in the blue light district of Berlin.

LED TUBES Conversion or retrofit kits for replacing fluorescent tubes by LED tubes are a questionable step backward [13].

It becomes even more ridiculous when during renovation when both the fittings for fluorescent lamps and the

conversion kit for LED tubes are ordered. The reasoning behind this is maybe that an IMB is still needed just in

case some time in the future an Electrically Insufficiently Instructed Person (EIIP)—intentionally or

unintentionally—replaces the LED tube by a fluorescent tube again. If during the replacement, the “EIIP”

forgets to remove the starter bypass for LED tubes, and there is no IMB anymore for fluorescent lamps, the

result would be a very loud bang.



Page 31

HOW TO YIELD ENERGY SAVINGS WITH LED TUBES

The efficiency level of LEDs is in general not represented by a figure in lumens per watt. We are told that this is

“not applicable” for LED lights. We are told once again that what counts is luminance in lux. What is left

unmentioned once again is the distance at which this luminance is measured.

If you measure the actual light output of LED tubes, you will soon discover that they do indeed come with

significant energy savings compared to the fluorescent tubes they replace. However, this would be like

replacing a 100 W incandescent light bulb by a 40 W incandescent light bulb, which also comes with a 60%

energy saving (Figure 28, Figure 29).

Figure 28 – This is how cost comparisons of LED and fluorescent tubes work: This bulb also has 60% potential

savings…



Page 32

Figure 29 – …if it is used to replace this bulb.

The argument that is used when claiming that fluorescent tubes can be replaced by less energy intensive LED

tubes is that LEDs only direct light to where it is needed. Although this argument holds for street lighting, this

is in general not the case for factory or warehouse areas. Actually, attempts are being made to spread light

from LED tubes more widely, since in factory and warehouse areas, light is needed pretty much everywhere. A

number of manufacturers are now proudly presenting 360° LED tubes in which the individual LEDs are laid out

in a circle, so that these tubes finally reproduce, to some extent, the properties of the fluorescent lights they

replace.

P I Φ h

min. 119.90 € Ratings 25.00W 1900lm 72lm/W

max. 119.95 € Measured 26.30W 119mA 1828lm 70lm/W

min. 77.52 € Ratings 25.50W 110mA 1650lm 65lm/W


min. 94.90 € Ratings 30.00W 2700lm


min. 2.37 € Ratings 58.00W 670mA 5200lm 90lm/W


T8 lamp Osram Lumilux 840

hereby replaced

VS

LN58.512

LOBS LED 30 W 5100-XL-DW-65

Type (device under test)

Philips Master LEDtube GA 1500

mm, 840 G13, 9290002904

With

ballast

type

AB

B

58

-15

0/2

3S

F-5

0-B

4

Price

OSRAM SubstiTube ST8-HA5-165-

840 Advanced



Page 33

Table 4 – Measured values and nominal values of power input and light flux with LED tubes compatible to a 58

W fluorescent tube (fluorescent tube: nominal values without, measured values with IMB).

From a technical point of view, it only makes sense to replace fluorescent tubes with LED tubes, if the original

fluorescent tube was hanging entirely free, sending its beam in all directions, while the application would in

fact require a proper fitting with reflectors to direct the light beam where it is needed. Instead of installing an

entirely new and more suitable fitting, replacing the fluorescent tube with an LED tube could be an equally

satisfying solution. See for example the makeshift arrangement in the hobby area in Figure 30 and Figure 31.

Both pictures were taken with the same aperture and exposure time. Light is needed most on the workbench,

and this workbench is just as well lit—with half the electrical power—in Figure 29 as in Figure 28. It was

therefore possible to halve the connected power by using directed light from LED tubes. Nowadays, it would

also have been possible to use warm tone LEDs to make the colour of the light in Figure 29 the same as that in

Figure 28. In that case however, there would be even less light in Figure 29.

However, from an economic point of view, it makes even more sense, in such a situation, to replace the old

fittings by a lower number of more suitable fittings with reflectors, and to lower the voltage. This would not

cost €60 per light, which is what LED tubes would cost.

It remains to be seen what 360° tubes will be good for. The only manufacturer to even give a price has not

really done itself a favour with a 20 W tube costing €89. There is no data available yet on the light flux of those

tubes.



Page 34

Figure 30 – In some cases, two fluorescent lights each with an equivalent nominal output of 58 W…



Page 35

Figure 31 – …can be replaced by two LED tubes of around 25 W…30 W each—but you should not expect the

same amount of light.

HOW TO INCREASE THE SERVICE LIFE WITH LED TUBES

We have shown that LED tubes are not more efficient, so the investment has to pay off in another way. LED

tubes are so expensive that they are only sold individually by electrical wholesalers, and not in packs of a

hundred like other lights. This means that if you replace a €3 fluorescent tube with a €60 LED tube, the LED

tube has to last at least 20 times longer for the investment to pay off. To replace a 58 W fluorescent light

which is being used correctly, with a correct tube fitting and reflectors when required, you need two LED tubes

costing a total of €120 to obtain the same objective amount of light.



Page 36

But in a factory which started this kind of nonsense, there is still a heated debate as to whether the lighting for

a new hall should be equipped with light fixtures designed for fluorescent tubes at the start, but which are

then to be used with LED tubes, or whether they should stick with good old fluorescent tubes this time. The

debate is not about energy efficiency, but about which light is more pleasant and which is warmer. That is

pretty much like extra-terrestrials who pay a fleeting visit to earth and see two cars, a red Volkswagen and a

blue Ford. When they go back to their galaxy, they report that there are two sorts of cars on earth, Ford cars

which are blue and Volkswagen cars which are red. Let me repeat it one more time: both fluorescent lights and

LED lights are available in almost any light-colour nowadays. The two types have many major differences, but

light colour is not one of them. However, when you compare Figure 28 with Figure 29 there are noticeable

differences in colour rendering. The two LED tubes in particular (although of different types and makes) have

clear weaknesses in red. But this has nothing to do with the principle and the opposite could have been true

with a different selection of samples.

It is a pity that the great invention of LEDs has been brought into disrepute. It is a scandal that even electrical

specialists do not always realize this. It cannot be said often enough: LEDs are valuable elements. But do not

misuse them. Do not lock them up in plastic tubes! The very existence of (even more expensive) 360° tubes

debunks the argument for using LED tubes to supply light only where it is needed. However, in many other

applications, this characteristic is indeed a major unique selling point for LEDs.

Service life is not a unique selling point. When fluorescent lamps are chosen and used correctly, their service

life can be just as long as that of LED tubes [12]. With the usual oblique approaches of comparisons applied, as

described in “The bluff factor in service life“, it is always possible to arrive at the desired result.

LEDS FOR STREET LIGHTING

The argument that LEDs provide a more directed light does hold for street lighting. In principle, a relatively

high amount of energy can be saved by using more directed light sources, since this drastically reduces light

diffusion. LEDs are very efficient at this, sometimes even too efficient, since they create highly lit areas right

next to pitch dark areas (Figure 32). It can also be seen that the conventional lighting in the background is

scattering its light in all directions, roughly in the photographer’s direction. The new LED lampposts prevent

this.

One solution might be to have a wide variety of sources of light with different lengthwise and crosswise angles

of scatter. It might also be possible to conceive a lighting module consisting of various groups of LEDs that can

be pivoted together. This would not make LED street lighting cheaper. Even if the extra cost for such a module

could be relativized against the price for an LED street lamp of around €500, there would also be considerable

expense involved in adjusting the lighting correctly. Moreover, this would have to be done at night to

immediately see the effects of adjustments.



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Figure 32: Incorrectly fitted LED lights: Brightly lit crossroads with blind spot in centre and each side street

plunged into darkness.

CONCLUSION: OUTLOOK We could arrive at the conclusion that LEDs are expensive and weak, their light is cold, and their energy

efficiency is no better than that of fluorescent lights, so they are not very suitable replacements. They are,

however, much more efficient than incandescent light bulbs and this alone would be a sufficient argument.

But efficiency in lumens per watt should not be pushed too much to the foreground either. LED bulbs today

can achieve similar values as fluorescent lights of comparable power. That is sufficient in itself and should help

convince buyers not to expect miracles. LEDs have refreshingly different properties, which justifies their

existence alongside, not instead of fluorescent lights. Apart from their level of efficiency, LEDs are so different

from fluorescent lights that they are used in other fields of application and markets, which until recently were

served by incandescent light bulbs, or were laying untapped. Competitive thinking is not appropriate. Stuffing

light diodes into a plastic tube, for example, which has the dimensions of a normal fluorescent light, is like

wanting to build a ship that is as fast as an airplane, or designing an airplane which can have as large a load as

a ship. It is pointless.

LEDs last for an extremely long time, work at practically any temperature, start right away and with a high

efficacy so, regardless of full or choked power, and are insensitive to frequent on/off switching. They are small,

compact, and highly focusable. They have developed incredibly quickly from use as simple indicator lights to a

practical source of light. It is to be expected that further advances will make LEDs suitable for other lighting

applications within a few years’ time. Dimming was not a feature that was asked for until quite recently, but it

is now available and is less expensive than for CFL. The availability of retrofit suitable bulbs for low voltage

halogen spotlights and main lights with standard sockets greatly facilitates the changeover. LEDs are an

economical replacement for incandescent light bulbs with regard to service life, even with today’s high

prices—provided the specified service life proves to be true (which may be questionable for a totally new

product with a very long life). Such a replacement is particularly advantageous when high costs are still

involved in changing lights. This was something the technical management of a high-class hotel found out. As is



Page 38

often the case, the hotel used energy guzzling halogen spotlights to light corridors day and night. They decided

to make the weekly check of lights easier by first replacing the halogen spotlights by LED spotlights in those

places that were difficult to access. The noticeably bluish light will remind them for a long time that these

lights were replaced before warm tone LEDs were introduced on the market, as they will still be working on

five years from now, even in constant use.

It is very important to note that LEDs are virtually an ideal replacement for incandescent light bulbs and are

much more efficient in such cases. They rarely make a good replacement for fluorescent lights – and if so, then

for different reasons than energy efficiency.

The ban on incandescent light bulbs will also make applications possible with LEDs which CFLs could not meet,

because of their cold start properties, their sensitivity to frequent switching, or due to their size. Low voltage

halogen lights are also incandescent lights and are simply enjoying a period of grace before the total ban on

incandescent light bulbs goes into effect. Anyone who still has lighting equipment with conventional 50 Hz

transformers instead of electronic converters by the cut-off point, will then only have to pull out the halogen

bulb and insert an LED bulb for the changeover to be complete. If the transformers have toroidal cores, the

level of losses will drop lower than anything which could ever have been achieved with electronic converters.

After such a changeover, transformers are only used to 20% of their capacity and toroidal core transformers

(Figure 33) then have amazing levels of efficiency (Figure 34).

Figure 33: Toroidal core transformers….



Page 39

Figure 34: …have particularly high efficiencies at low load.

Unfortunately, you still hear things today like “due to the complex manufacturing process of light diodes, the

typical values shown for the technical parameters of LEDs are only statistical values, which do not necessarily

correspond to the actual technical parameter of a given product” [15]. But that is like saying the average light

flow of an entire batch of LEDs may well be correct, but a single end user might end up with an LED that does

not light at all, while the next user is lucky to have one that shines twice as brightly. The statement is obviously

not meant to be that extreme, as there are still technical tolerances that single LEDs must conform to. Never

forget that the light flow specifications of other types of light sources are also derived from averages of a trial

sample, and these values are then combined with absolute tolerances. This is a reasonable practice. The

problem with LEDs, however, is that the tolerance framework is not made public. Far from where the user is

buying the product [9], a data sheet for technicians holds the secret: “Brightness groups are tested at current

pulse duration of 25 ms and with a tolerance of ±11%”. But in the user’s data sheet, there is not a single

reference to this tolerance. In this way, what could be a reasonable practice becomes a malicious misleading of

customers.

0%

20%

40%

60%

80%

100%

0% 25% 50% 75% 100% 125% 150% 175% 200%

η

I/IN

η, 400 VA standard transformer

η, 400 VA toroidal core transformer



Page 40

REFERENCES [1] www.krucker.ch/Skripten-Uebungen/AnSys/ELA4-D.pdf and many other sources of information if you

search the internet for “LED” and “thermal stress”

[2] www.sott.net/articles/show/244434-Forget-WiFi-and-Radio-Waves-LiFi-Uses-Lightbulbs-to-Connect-to-the-

Internet

[3] EN 61000-3-2:2006-10 (VDE 0838-2:2010-03)

[4] Stefan Fassbinder: “Ersatz von Halogenspots durch LED-Leuchtmittel”. Elektropraktiker 11/2010, p 938

[5] For example: www.neumueller.com

[7] www.dial.de

[8] http://heatball.de

[9] www.rsdobrasil.com.br/produtos_arquivos/6f14658078a36e7f953d1af7f5ad837d_23112010111119_.pdf

[10] www.intematix.com

[11] Christoph Lehnberger: “Entwärmung von elektronischen Baugruppen”. Elektropraktiker 2/2012, p 120,

Figure 8

[12] Stefan Fassbinder: “Leuchtstofflighten-Lebensdauer und Schalthäufigkeit”. Elektropraktiker 4/2012, p. 316

[13] The Latin word “retro” = back

[14] Stefan Fassbinder: “VVG-Vorschaltgeräte in der Beleuchtungstechnik”. Elektropraktiker 4/2005, p. 284

[15] http://www.osram.com/osram_com/products/lights/led-retrofit-lights/professional-led-lights-with-classic-bulbs/

parathom-classic-a/index.jsp

http://www.osram.com/osram_com/products/lamps/led-retrofit-lamps/professional-led-lamps-with-classic-bulbs/parathom-classic-a/index.jsp

http://www.osram.com/osram_com/products/lamps/led-retrofit-lamps/professional-led-lamps-with-classic-bulbs/parathom-classic-a/index.jsp

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