Light emitting diodes (LEDs) have gained
broad recognition as the ubiquitous little lights that tell us that our
monitors are on, the phone is off the hook or the oven is hot semiconductor.
The basic principle behind the emission of light is that: When charge carrier
pairs recombine in a semiconductor with an appropriate energy band-gap
generates light. In a forward biased diode, little recombination occurs in the
depletion layer. Most occurs in a few microns of either P- region or N –region,
depending on which one is lightly doped. LEDs produce narrow band radiations,
with wave length determined by energy band of the semiconductor.
Solid state electronics have replaced their
vacuum tube predecessors for almost five decades. However in the next decade
they will be brighter, more efficient and inexpensive enough to replace
conventional lighting sources .
Recent development in AlGaP
and AlInGaP blue and green semiconductor growth technology have enabled
applications where several single to several millions of these indicator LEDs
can be packed together to be used in full color signs, automotive tail lambs,
traffic lights etc.
Artificial lighting sources share
three common characteristics:
-They are rarely viewed directly: light
from sources are viewed as reflection off
the illuminated object.
- The unit of measure is kilo lumen or
higher not mille lumen or lumen as it is incase of LEDs
-Lighting sources are pre dominantly
white with CIE color coordinates, producing excellent color rendering
Today there is no such commercially
using “SOLID STATE LAMP” However high power LED sources are being developed,
which will evolve into lighting sources
White Led
Technology
Illumination means white light, and a
very particular kind of white light at that. Having evolved under a black body
emitter, the sun, with a correlated color temperature (CCT) in the 3000 K–6500
K range depending on time of day, weather and season, the human eye is quite
sensitive to small changes in spectral content of illumination sources. Even
though a white light source may have color coordinates close to the black body
curve, the source may not render true colors when used to illuminate an object.
If the wavelengths reflected by a surface are absent in the source, then the
surface will appear dark or gray, not colored. Upon reflection or transmission,
spectrally incomplete sources will produce less vivid color quality than those
with a more complete spectrum. The ability of an illumination source to render
true colors is determined by measuring the color rendering index, Ra, scaled 0
to 100. The noon-day sun, incandescent lamps and other near black body
radiators have Ras of near 100. Thus the White LED should be able to produce
white light with high CRI.
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