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Light-Emitting Diodes
Light-Emitting Diodes 121
Figure 6.12. The reason why texturing the surface is an interesting idea can be appre-
ciated from the results that compare the external efficiency before and after the opera-
tion. Texturing more than triples the external efficiency. Taken from I. Schnitzer et al.,
Applied Physics Letters 63, 2174 (1993). Reproduced by permission from the American
Institute of Physics.
Emission band = assume to be uniform from 400 nm to 1900 nm
Bulb replacement once per year, half hour labor for two men @
$40/hour loaded salary
Red light diameter = 200 mm
Passband for filter used to generate red light = 100 nm
The red filter allows 1 part in 15 of the emitted optical radiation
through. The bulb is 15% efficient to begin with.
Total emitted optical power = 15 W
Total emitted red light = 15 × 1/15 = 1 W
Light-emitting diodes
Assume each LED emits 1 mW of optical power in the red
Quantum efficiency = 4%
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