|Re: Green LED's?|
Message #8 Posted by Andrés C. Rodríguez (Argentina) on 22 Nov 2003, 10:00 a.m.,
in response to message #1 by Katie
Katie: I think I haven´t seen any "real green LED" calculators, I could remember that green LEDs were anything but common before 1980 (of course in my country, but also in most USA and european electronics magazines I was subscribed to). Even the "activity" or "power on" LED in commercial computers (i.e.: Data General, IBM, Compaq, Bull), disk drives (Shugart, Seagate, Fujitsu), early PCs, floppy drives were usually red until 1988 and even later.
I assume that the higher cost and, for portable equipment, power budget could have been barriers for massive adoption of non-red LED. I vaguely remember something about GaAsP vs. GaP processes that may also have something to do with cost and availabity.
As the light wavelength relates with the voltage drop in LEDs by means of the equation E=hf, where E is the energy in electron volt units, h is Planck constant andf is the frequency, it follows that green (and yellow) LEDs have a higher operating voltage than red ones. While the greater eye sensibility for green may reduce operating currents, I think that the voltage issue may have been a factor preventing a faster adoption for portable electronics.
Edited: 22 Nov 2003, 4:12 p.m. after one or more responses were posted