Lighting and the Visually Impaired

By Bryan Gerritsen,

Certified Low Vision TherapistCopyright 2012

Including discussion of different types of lighting

And with special emphasis on LED Lighting

To begin, first a question:

What is Light?

Light is made up of

electromagnetic particles that travel in waves.

Our retinas are capable of responding to only a small part

of the entire electromagnetic spectrum.

From the longest waves (lowest frequency) through the shortest waves (highest frequency), lighting specialists identify the electromagnetic wave regions as

1) radio waves, 2) microwaves and radar, 3) millimeter waves and telemetry, 4) infrared,

5) visible light, 6) ultraviolet,and 7) x-rays and gamma rays.

                                                                                                                      

Wave Lengths are measured in “Nanometers”

Not all wavelengths are visible to the human eye. For the most part, this presentation will be limited to

visible light.

Definitions

• Nanometer (nm) is a measure of the length of the light waves

• A nanometer is the extremely small unit used to measure lengths of light waves.

• One nanometer equals • one billionth of a meter.

Definitions

• Correlated Color Temperature (CCT) is a measurement of the actual color appearance of light. It is expressed in Kelvins (K). Low CCT numbers define “warm” lighting like yellow and red hues of candlelight at 1500K. High CCT numbers define “cool” light, like blue (5000K to 7000K).

Definitions

• Kelvin is the basic unit of measurement for temperature

• The Kelvin temperature rating is based on the color most highly emitted

Definitions

• Footcandle (fc) and LUX (lx) are units of illuminance, measuring light on the surface

• 50 footcandle is generally considered sufficient for many tasks

• Higher footcandles may be needed to do fine work such as threading a needle

Definitions

• Lumen (lm) is a measurement at the light source (the lamp), and not necessarily at the surface being lit

• It is the standard unit of luminous flux (the time rate of flow of radiant energy)

Definitions

• A watt is a unit of power equal to work done, at the rate of one joule

• Wattage is actually a measurement of energy, not of light

Ultraviolet Waves are very short wave lengths of light that are not

visible to the Human Eye

• UV-C are in the range of 100-290 nm

• UV-B are in the range of 290-320 nm

• UV-C are in the range of 320-400 nm

• UV-B gets most of the blame for damaging the eyes, skin, and materials

• UV light is to the left of visible light on the light spectrum

Infrared Light

• Is also invisible to the human eye

• The term "Infra-" means "lower than”

• It has longer wavelengths than those of the visible light spectrum

• It is to the right of visible light on the light spectrum

Infrared Light

• Energy whose wavelength is too long to see is "redder than red“ or Infrared.

• How do we know this kind of light exists? • One way is that we can feel energy with

these wavelengths such as when we sit in front of a campfire or when we get close to a stove burner.

• Very long wavelengths of infrared light radiate heat to outer space.

The visible light spectrum ranges from about 400 nm (shortest)

to about 700 nm (longest)

The “visible light spectrum” is that small part of the electromagnetic wave spectrum that we see

as colors.

• Red

• Orange

• Yellow

• Green

• Blue

• Indigo

• And violet

From highest nanometers (700)to the lowest (400), the colorsof visible light in order are:

The visible light spectrum is shown in the diagram below.

                                                                                                         

 

Light is needed to trigger the cone cells on the retina,

in order to read, to see details, and to do all tasks

As we get older, we generally need more light to read and to do near tasks

• A German study stated that:

• A 50 year-old likely needs 10 times as much light as a 10-year old to read

• A 65 year-old likely needs 15 times

as much light as a 10-year old to read

In addition, the Need for Illumination

is much greater for a person with a Vision Impairment

• They will likely need 3-4 times as much light as a person their age, who does not have a vision impairment

Specifically, persons with a central field loss (such as AMD

or diabetic retinopathy)

• Will have damage to their cone cells

• Which are key in transmitting signals of light received to the visual cortex of the brain

• Therefore, they need improved illumination for near tasks

The Need for Illuminationfor Persons with Low Vision

• Is highest in persons with retinal involvements such as– AMD– Stargardts– Bests Disease– Retinopathy of Prematurity– Histoplasmosis– Toxoplasmosis

The Need for Illumination

• Is also high for persons with:– Optic Atrophy

– Retinitis Pigmentosa

– Glaucoma

– Cataracts

Research by Guinilla Portnoy, O.D.and John Brabyn, Ph.D.

revealed that:• An 85-year old person who has 20/40

visual acuity in a high brightness setting and with normal or high contrast materials

• Only has 20/200 visual acuity in a poor brightness setting and with low contrast materials

Many doctors or low vision specialists try to help that person

read more easily merely with a magnifier or with reading glasses

I’m certainly not saying or suggesting that a magnifier or

reading glasses are not needed or will not be helpful

for a person with 20/40 or 20/70 or any other

diminished visual acuity

But perhaps what is needed most for that person,

or is as equally important as a magnifier is:

• Illumination

• Illumination

• Illumination

How much light is needed?

Are there standards of how much light is needed for specific tasks?

It is partially dependent on:

• The contrast of the item vs. its background

• The size of the target being viewed

• The age of the person doing the task

• Whether the person has a visual impairment and needs additional light

Lighting needs may also vary according to:

• Orientation (south vs. north facing room

• Weather (cloudy vs. sunny day)

• Time of day (position of the sun in the sky)

• Season (position of the sun)

Different tasks and targets also require varying levels of illumination

• Reading items written in a #2 pencil, vs. those written with a pen vs. those written with a felt pen

• Reading items on a blackboard vs. those on a whiteboard

• Seeing a ball in the gymnasium vs. threading a needle ins the sewing room

Sample lighting standards for different rooms or areas:

• Bathroom 20 fc• Cafeteria or snack bar 20 fc• Kitchen 50 fc• Classroom 45-55 fc• Library or study area 45-55 fc• Computer room 40-70 fc• Clerical or secretarial areas 60-70 fc• Shops or special labs 50-100 fc

From Michigan Tech and Adopted fromFederal Energy Administration Guidelines

Lighting is dependent on the contrast and the size of the target

Visual tasks with:• High contrast and large size 30 fc• High contrast and small size 50 fc• Low contrast and small size 100 fc• Extremely low contrast and

small size 300-1000 fc

Standards by the Illuminating and Engineering Society of North America (IESNA)

These standards just given are for people with “normal” vision

Please remember that

a person with a vision loss may need about 3 times as

much light for near tasks as a person with normal vision

The amount of light needed for a person with a vision loss

for reading

Is closely related to their score on a Contrast Sensitivity

Function (CSF) test

Persons with poor contrast sensitivity function need very bright illumination for reading

Persons with better contrast sensitivity function (CSF) do not need as much light for reading

Gerritsen and Christiansen, 2006

How do we Measure Light in a Room or for a Task?

Lighting is measured with a light meter

at 30 inches above the floor, at various points in the room

A mathematical average

is then taken.

Light on a surface can be measured with a Light Meter

in Footcandles (or Lux)

Measure the light for your students, clients, or family member with a light meter to help determine if lighting is sufficient for the task they are

trying to do

The ratio of illumination in a room

• Should be approximately 5:3:1

• Between the page, the desk, and the room

• This same ratio applies to a CCTV screen, the working desk, and the rest of the room

An important principle is not just the amount of light, but

the position of the light

Therefore, it is important to talk about something called the

“Inverse Square Law” of lighting

Illumination Uses the“Inverse Square Law”

That means that as a light source gets closer, the amount of light

delivered is squared

Thus, if a lamp used to be2 feet away

• And we move it closer so that now it is 1 foot away,

• It is not twice as bright, as we may suppose;

• Instead, it is 4 times as bright, since we square the amount of light delivered

Then if we bring it closer again, moving it from 1 foot away

to 6 inches away

• We square the amount of light delivered again

Perhaps the Best Way to Make Use of the

“Inverse Square Law”of Lighting

• Is to bring a lamp closer

Improved Illumination is notSo Much a Factor of the

Type of Light, or Even theWattage of Light Bulb

• Instead, it is mostly a factor of the

• Position of the light, using the Inverse Square Law

We Can Bring a Lamp Closer

• By using a gooseneck or swing arm

–Desk lamp

–Floor lamp

–Clip-on lamp

There are many types of Light

• Sunlight

• Incandescent

• Fluorescent

• Halogen

• Light Emitting Diodes or LED

• “Daylight” or Full Spectrum

A lamp is not the fixture that holds the light bulb or tube,

Nor is it a light

• A lamp is the light bulb or tube itself which is contained in the fixture

• Light is the energy that emits from the lamp

Types of Lamps—Incandescent

Incandescent Lamps

• Contain a tungsten filament in a vacuum

• An electrical current causes the filament to glow (incandesce)

Incandescent Lamps

• Features a warm yellowish light

• With little glare

• Provides excellent contrast

• Are very helpful for “task” lighting

They have a low Kelvin rating—generally about

2700K to 3200K

Therefore they do not

emit any ultraviolet or “blue” light

Incandescent Lamps

• However they can be warm to work under

• They may have less even lighting and more shadows than fluorescent lamps

• They generally cost more to operate than fluorescent lamps

Incandescent Lamps mayBe on their Way Out

• Congress has passed laws that will likely eliminate production of most incandescent lamps by the year 2014

• However, incandescent lamps will probably still be around for several years after that, as will some replacement bulbs

• Incandescent lamps will continue to have several strong advantages—e.g. high contrast and minimal glare for the VI

Some specialty incandescent bulbs

and lampswill still be allowed and

produced after 2014

Types of Lamps—Halogen

Halogen Lamps

• Contains a filament made of tungsten, so it is a type of incandescent lamp

• However, it is different than a normal incandescent lamp, because it also contains the gas halogen

• Halogen recycles the burned particles of tungsten, constantly rebuilding the filament and giving it a longer life

Halogen Lamps

• Provide very bright illumination—perhaps the brightest

• Have a “white” light appearance

They also have a lowKelvin rating—generally about

3700K to 3900K

Therefore they also do not emit any ultraviolet or “blue” light

Halogen Lamps

• But by “pushing” the brightness the contrast may be slightly diminished or decreased

• They are very hot to work under and dangerous to touch

• Because it is so hot, It can be a safety hazard if not properly used

Types of Lamps—Fluorescent

Fluorescent Lamps

• Is a phosphor-coated tube filled with mercury and argon vapor

• An electrical current discharged into the vapor causes the phosphor to glow (fluoresce)

• The type and blend of phosphors used in the coating determine the color of emitted light

Fluorescent Lamps

• Provides even lighting

• With few shadows

• Is cool to work under

• May be a good choice for room lighting

They have a slightly higher Kelvin rating—generally about

4,200K to 4900K

Except for some models, they generally do not emit ultraviolet light,

and do not emit “blue” light

Fluorescent Lamps

• May create glare for some persons

• May not provide as good contrast as incandescent lamps

Types of Lamps— “Full Spectrum”

Full Spectrum Lamps

• Are a type of fluorescent lamp

• Generally have a Correlated Color Temperature (CCT) of 5,000K (Kelvin) or higher

• And a Color Rendering Index (CRI) of 90 or higher

• Often have enhanced levels of Ultraviolet (UV) light

Full spectrum or “Daylight” lamps generally have a high Kelvin rating—

5,000K to 6,500K

They will emit both ultraviolet and “blue” light

Full Spectrum or“Daylight” Lamps

• Mimic natural sunlight• May have the same phosphors as sunlight• Have an even light• Are cool to work under• Are excellent for color matching, quilting,

painting, art work, and hobbies• May have applications in professional settings

such as dental work, for color matching

Full Spectrum Lamps

• Often have “blue light” and may have ultraviolet light (UV-A and UV-B)

• May have diminished contrast, especially if over 5,000 K

• Therefore may not be the best for persons with low vision, if they are concerned about blue light and UV, or if they need enhanced contrast

Types of Lamps—LED’s

(Light Emitting Diodes)

LED Lamps

• Are a semiconductor device

• With a variety of phosphors, rare earth elements, scintillators, or quantum dots

• Which produce electroluminescence

Colors of LED’s

• The color of emitted light depends on the chemical composition of the semi-conducting material used.

• It can be near-ultraviolet (NUV), visible or infrared. The first practical visible spectrum LED was produced in 1962. Red and greens were available first, then blues in 1993.

• White LED’s became available in 1996.

LED Lamps

• May have a lower Kelvin rating of 2,700K to 4,500K— “warm” white, OR

• A high Kelvin rating of 5,000K to 6,500K— “cool” white or “daylight” white)

• Two LED lamps can be on the shelf next to each other, look alike, cost the same, and be made by the same manufacturer

• One may be rated as 3,200K, and the other at 6,500K

A “warm” LED lamp will not emit any UV or “blue” light

A “cool” LED lamp may emit both UV and blue light

LED Lamps

• “Warm” LED’s may not be as bright as “cool” or “daylight” LED’s

• However, they do not emit UV or “blue” light like a “cool” LED may

• To compensate, you can choose a higher output (lumens) lamp or position it closer

LED Lamps

• Are extremely energy efficient

• And can last an incredibly long time (up to 50,000 hours—perhaps several decades)

• Compare this to about 1,000 hours for an incandescent bulb or 7,500 hours for a compact fluorescent (CFL) bulb

• Thus, an LED lamp can last at least 4 times, and perhaps 7 times longer than a compact fluorescent (CFL) bulb

When do LED Bulbs wear out?

• They don’t just burn out; instead they very slowly become dimmer with age and use

• The Lighting Research Center (LRC) defines useful life of LED lamps as the point at which light output declines to 70% of initial lumens

• Most manufacturers estimate a lifetime of 30,000 hours to the 70% lumen maintenance level

As LED durability continues to improve, some LED’s are rated

to last at this 70% level to 50,000 hours

If used an average of 3 hours a day, this would mean a useful life of 27-46

years, allowing for the 30% lumen depreciation

LED Lamps

• Are often more than a single diode—they may have multiple diodes, a chip, or a multi-chip, perhaps even several layers

• They may have a more narrow beam or “spread” than other lamps

An important feature to consider when choosing an LED lamp is its “spread,” or

the width of the light beam it produces

Try to select an LED lamp that produces a fairly wide beam

of light

LED Bulbs• Now come in an Edison (E-26 or E-27)

base, and will work in existing household lamps and light fixtures, as direct screw-in replacements (as little as $6 to $24)

LED Lamps• Are increasingly taking over the market formerly

held by incandescent and fluorescent lamps• Because of their amazing longevity and energy

efficiency• Also, they are encased in hard plastic (rather

than glass), so they don’t break, and are shock resistant

• And, they do not contain mercury like CFL bulbs (a problem when disposing of CFL’s)

LED Lamps• Can even be battery operated, which

makes them very portable

Other LED Lights—Headlamps, Flashlights,

and Stick-on Lights

LED lamps may be a wonderful option for persons

with a vision loss

As table lamps, floor lamps, flashlights, “stick-on” lights, and headlamps. Also, remember that replacement bulbs are

now available in LED

In the future, organic LED’s (OLED’s) may become available. They create light on an ultra-thin

sheet. They could illuminate:

• Ceiling tiles

• Venetian blinds

• TV screens and computer monitors

• Mobile phones

“Blue light” are short wave lengths on the

nanometer scale of visible light

• That range from about 400 nm to 470 nm

• They are visible to the human eye

• And are perceived as the color blue

Laboratory studies on animalsseem nearly unanimousthat blue light causesmacular degeneration

However, real world studies on people have produced conflicting

results

Blue light and macular degeneration (AMD)

• Some studies positively link AMD with any kind of light exposure

• Other studies have found a weak correlation between AMD and blue light exposure

• Yet a third group of studies has found no correlation between AMD and sunlight

One Australian study concluded that the problem is not total sun exposure, but how sensitive you

are to the sun

This study also concluded that people with blue irises are at

increased risk for AMD

People with blue or light-colored eyes and fair skin may be particularly susceptible to

macular damage from blue light because they have less melanin

in their irises.

Melanin protects the macula by trapping light rays so they don’t

reach the macula and cause damage

In short, we probably cannot say at this time that blue light

positively contributes to macular degeneration

But the plausibility and probability is certainly there

Therefore, because of a possible link and possible benefit:

• Exposure to blue light should

possibly be limited

Also, “Blue blocker” sunglasses should be worn

• Especially if you have blue or light colored eyes and fair skin

• Or if you have other risk factors

• Or if you spend lots of time in bright sunlight or on water, sand, or snow, which reflects sunlight

• A sun visor or hat may also be helpful

The color that blocks blue is yellow, so blue blockers must

contain a yellow tint

• This includes sunglasses and glare shields with that are:

• Amber

• Orange

• Amber/orange

• Yellow and

• Plum

Problems with Some Lamps

Some lamps provide some concerns, because they

may emit UV light and/or blue light

Fluorescent Lamps

• In common fluorescent tubes, UV rays are mostly blocked by the glass enclosure

• Blue light, however, may pass through unimpeded

• Fluorescent tubes containing the older halophospate type phosphors emit light that is high in the blue spectrum

Full Spectrum Lamps

• Often contain the visible blue light spectrum and the invisible UV light

• If they are rated with a CCT (Correlated Color Temperature) of 5,000K or higher (which almost all do)

Full Spectrum Lamps rated at 5,000K or higher, and therefore

have blue and UV light include the

• Ott Lite (5,000K)

• Vita Lite (5,000K) and

• Vital Lite Plus (5,500K)

• Verilux Happy Eyes (5,500K)

• UltraLux (5,500K)

• VisionMax Full Spectrum (6,500K)

• Sunlight Lamp by Bell & Howell (6,500K)

Other Full Spectrum Lamps rated at 5,000K or higher

• “Bright as Day” by Sharper Image (5,000K)

• PureLite (5,000K)• BioPure Full Spectrum (5,500K)• Life Lite by True Scan (5,500K)• Paralite-Specra 5900 (5,900K)• Balanced Spectrum (6,500K)• Lumichrome (6,500K)• Coil-Lite Compact Fluorescent (6,500K)• And many others

LED Lamps

• Those rated over 5,000K contain blue light

• Care should be taken to ascertain the Kelvin rating of LED lamps or bulbs, since two could be made by the same manufacturer and be sold alongside each other on a shelf in a store, or on the same page in a catalog. One could be rated 3,200K (“warm”), and the other 6,500K (“cool”), and look almost exactly alike.

One author wrote, “Just as we shield our skin from prolonged sunlight, it makes sense that

we should also shield our eyes when outdoors.”

He continues, “Until good science provides more definite

answers, we might also be wise to not bring the sun into our houses and place it on

our desktops.”

However, even if we do not accept research thus far about

any possible link between blue light and retinal damage

(such as with macular degeneration),

or completely put any concern aside about

blue light . . .

Another important concern about lamps with a CCT of

5,000K or more

• Is their diminished contrast• As we push the brightness of a lamp,

we often sacrifice or diminish contrast

• Good contrast is generally very important for a person who is visually impaired

Finding lamps with a CCT Correlated Color Temperature of

4,900K or less will help to

• Avoid having blue light and UV light in the lamp

• Increase the contrast, which is so important to a person with a vision loss

Glare should be avoided

By carefully watching the positioning of lighting

coming into the eye, and of items being viewed

in relationship to light sources

Note floor and table lamps, TV, and windows

Glare can also be minimized by wearing glare shields

• Amber, amber/orange, orange, or plum for bright or sunny days

• Yellow colored for indoors by a window, for cloudy days, or for early morning or late afternoon conditions

Bryan GerritsenCLVT

Low Vision Rehabilitation Services (LVRS)

www.LowVisionRehabServices.cominfo@LowVisionRehabServices

Copyright

2012