[sdiy] Re: Vactrol (opt align) VCF rev 2: help needed

[mirwin at qouest.net]

The white LEDs are efficient enough that the glow can be seen even with 
only one microamp flowing (in a dark room..)... even  skin conduction 
and a 6V battery is sufficient. The phosphor has a half-life of only 
2000 hours though (last time I looked up the specs, maybe they are 
better now). The blue chip will glow, but the phosphor 
gradually loses it's ability to fluoresce with extended usage. White 
LED's with diffused cases are available, might be the best choice if you 
use one of these. Don't know if these would really be any better than a 
diffused hi-efficiency red or green LED though, shining on a ring of 
matched LDRs (what I normally use).
Cheers, Mike
P.S. fasten LDR's to an oscilloscope CRT and play with the focus knob 
and different waveforms!!!