Page 147 - Photonics Essentials an introduction with experiments
P. 147
Light-Emitting Diodes
Light-Emitting Diodes 141
6.6 It is now common to find traffic lights with the red light com-
posed of LEDs and a red filter instead of an incandescent light
bulb. However, it is less common to find a traffic light with a
green LED signal, and even less common to find a traffic light
with an amber LED signal.
a) Explain the rarity of green LED signals. Is this a technologi-
cal or an economic problem? Is the economic issue related
more to the cost of the LED light or the difficulty of saving
money during operation?
b) Explain the even greater rarity of amber LED traffic lights by
answering the same questions as in Problem 6.6a. Are there
other applications in which amber LEDs could be used?
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