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Description of various white light emitting
sources.
Incandescent lamp
An incandescent light bulb is an electric lightwhich produces light with a
wire flamentmade o tungsten (or earlier, carbon) heated to a high temperature
by an electric current passing through it, until it glows. The hot flament is
protected rom oxidation within a glass or quartz bulb enclosure that is flled with
inert gas or eacuated. The bulb is flled with an inert gassuch as argon(!"#)
and nitrogen($#) to reduce eaporationo the flament and preent
its oxidationat a pressure o about $% &'a. A %% light bulb or *% +
operation emits about ,$%% lumens, about 17 lumens/W. ncandescent lampsare relatiely inexpensie to ma&e. The typical liespan o an A- incandescent
lamp is $% to ,%%% hours.
ncandescent bulbs are manuactured in a wide range o sizes, light output,
and oltageratings, rom . olts to about "%% olts. They require no external
regulating equipment, have lowmanuacturing costs,and wor equall!
well on either alternating current or direct current.
ncandescent bulbs are much less e"cientthan most other types o electric
lighting/ incandescent bulbs conert less than # o the energy they use into
isible lightwith the remaining energy being conerted into heat.
The luminous e0cacyo a typical incandescent bulb is 1# lumens per watt,
compared to the 1% lm2 o a compact 3uorescentbulb. ncandescent bulbs
typically hae short lietimes compared with other types o lighting/ around
1,$$$ hoursor home light bulbs ersus typically %,%%% hours or compact
3uorescents and "%,%%% hours or lighting 456s. ncandescent bulbs are
gradually being replaced in many applications by other types o electric light,
such as 3uorescent lamps, compact 3uorescent lamps (-74), cold cathode3uorescent lamps(--74), high8intensity discharge lamps, and light8emitting
diode lamps(456)
9ost light bulbs hae either clear or coated glass. The coated glass bulbs hae a
white powdery substance on the inside called &aolinwhich is a white, chal&y clay
in a ery fne powder orm, that is deposited on the interior o the bulb. t
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di:uses the light emitted rom the flament, producing a gentler and eenly
distributed light.
%alogen lamp
A halogen lamp is an incandescent lampthat has a small amount o
a halogensuch as iodineor bromineadded. The combination o the halogen gas
and the tungstenflament produces a halogen c!clechemical reaction which
redeposits eaporated tungsten bac& onto the flament, increasing its lie.
;ecause o this, a halogen lamp can be operated at a higher temperature than a
standard gas8flled lamp o similar power and lietime, producing light o a
higher luminous e0cacy.
&luorescent 'amp
A (uorescent lampor a 3uorescent tube is a low pressure mercury8apor gas8
discharge lamp that uses 3uorescence to produce isible light. An electric
current in the gas excites mercury apor which produces short8wae
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ultraiolet light that then causes a phosphor coating on the inside o the bulb to
glow.
-onentional linear 3uorescent lamps hae life spans around )$,$$$ and
*$,$$$ hours.
hen light is turned on, the electric power heats up the cathode resulting in
thermionic emission. The emitted electrons collide with and ionize the gasatoms
inside the bulb surrounding the flament. the incident ree electron has
enough &inetic energy, it transers energy to the atomg, these photons hae waelengthsin the ultraiolet(?+)
region o the spectrum (*".$ and @ nm). These are then conerted to isible
range by ma&ing use o 3uorescence. 4ight8emitting phosphors are applied as a
paint8li&e coating to the inside o the tube. This coating absorbs the ultraiolet
photons, causing a similar =ump and drop process, with emission o a urther
photon. The photon that is emitted rom this second interaction has a lower
energy than the one that caused it and lies in isible region. The di:erence in
energy between the absorbed ultra8iolet photon and the emitted isible light
photon goes toward heating up the phosphor coating.
7luorescent lamps must use an auxiliary deice, a ballast, to regulate the
current 3ow through the lamp. >igher quality 3uorescent lamps use either a
higher - halophosphate coating, or a triphosphormixture, based
on europiumand terbiumions, that hae emission bands more eenlydistributed oer the spectrum o isible light
%igh+intensit! discharge lamp
%igh+intensit! discharge lamps(%ID lamps) are a type o electricalgas8
discharge lampwhich produces light by means o an electric arc
between tungstenelectrodeshoused inside a translucent or transparent used
quartzor used aluminaarc tube. This tube is flled with
both gasand metalsalts. The gas acilitates the arcigh8intensity discharge lamps are a type o arc lamp
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>igh8intensity discharge lamps ma&e more isible light per unit o electric power
consumedthan 3uorescentand incandescentlamps since a greater proportion o
their radiation is isible light in contrast to inrared.
'D lamp
An 'D - light8emitting diode)lamphae a liespan and electrical e0ciencythatis seeral times better than incandescent lamps, and signifcantly better thanmost 3uorescent lamps, with some chips able to emit more than 1$$ lumensper watt.
4i&e incandescent lamps and unli&e most 3uorescent, 456s come to fullbrightness without need for a warm+up time/ the lie o 3uorescent lightingis also reduced by requent switching on and o:. nitial cost o 456 is usuallyhigher. 6egradation o 456 dye and pac&aging materials reduces light output tosome extent oer time.
456s do not emit light in all directions, and their directional characteristics a:ectthe design o lamps. The light outputo single 456s is less than that oincandescent and compact 3uorescent lamps/ in most applications multiple 456sare used to orm a lamp.
456 chips need controlled direct current(6-) electrical power/ anappropriate circuitis required to conert alternating current rom the supply tothe regulated low oltage direct current used by the 456s. 456s are aderselya:ected by high temperature, so 456 lamps typically include heatdissipationelements such as heat sin&sand cooling fns.Ceneral8purpose lighting needs white light. 456s emit light in a ery narrowband o waelengths, emitting light o a color characteristic o theenergy bandgapo the semiconductormaterial used to ma&e the 456. To emitwhite light rom 456s requires mixing light rom red, green, and blue 456s, orusing a phosphorto conert some o the light to other colors.
ompact (uorescent lamp
A compact (uorescent lamp(&') is a 3uorescent lampthat uses a tube
which is cured or olded to ft into the space o an incandescent bulb, and a
compact electronic ballastin the base o the lamp.
Theyhae seeral small8diameter tubes =oined in a bundle o two, our, or six, or
a small diameter tube coiled into a helix, to proide a high amount o light
output in little olume. -ompact 3uorescent lampsare now aailable in the same
http://en.wikipedia.org/wiki/Luminous_efficacyhttp://en.wikipedia.org/wiki/Luminous_efficacyhttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Incandescent_light_bulbhttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Electrical_efficiencyhttp://en.wikipedia.org/wiki/Incandescent_light_bulbhttp://en.wikipedia.org/wiki/Fluorescent_lampshttp://en.wikipedia.org/wiki/Luminous_fluxhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/LED_circuithttp://en.wikipedia.org/wiki/Thermal_management_of_high-power_LEDshttp://en.wikipedia.org/wiki/Thermal_management_of_high-power_LEDshttp://en.wikipedia.org/wiki/Heat_sinkhttp://en.wikipedia.org/wiki/Fin_(extended_surface)http://en.wikipedia.org/wiki/Bandgaphttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Phosphorhttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Electronic_ballasthttp://en.wikipedia.org/wiki/Compact_fluorescent_lamphttp://en.wikipedia.org/wiki/Compact_fluorescent_lamphttp://en.wikipedia.org/wiki/Luminous_efficacyhttp://en.wikipedia.org/wiki/Luminous_efficacyhttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Incandescent_light_bulbhttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Electrical_efficiencyhttp://en.wikipedia.org/wiki/Incandescent_light_bulbhttp://en.wikipedia.org/wiki/Fluorescent_lampshttp://en.wikipedia.org/wiki/Luminous_fluxhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/LED_circuithttp://en.wikipedia.org/wiki/Thermal_management_of_high-power_LEDshttp://en.wikipedia.org/wiki/Thermal_management_of_high-power_LEDshttp://en.wikipedia.org/wiki/Heat_sinkhttp://en.wikipedia.org/wiki/Fin_(extended_surface)http://en.wikipedia.org/wiki/Bandgaphttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Phosphorhttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Electronic_ballasthttp://en.wikipedia.org/wiki/Compact_fluorescent_lamphttp://en.wikipedia.org/wiki/Compact_fluorescent_lamp -
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popular sizes as incandescent and are used as an energy8saingalternatie in
homes. &'s use one+fth to one+third the electric power,and last eight to
fteen times longer as compared to incandescent lamps. A -74 has a higher
purchase price than an incandescent lamp, but can sae oer fe times its
purchase price in electricity costs oer the lamp