[Laser] LEDs as photodiodes

[steve kavanagh]

Hi Stuart

Yes, I've seen the material you refer to.  It's initially amazing to see
that the power LEDs work well.  But then, they are designed for maximum
efficiency in emitting mode, so probably many losses which affect
photodiode mode efficiency are minimized as well.  I am suspicious that
some of the small LEDs may have quite significant losses (absorption in
the material, reflection losses, poor optics, etc.), particularly when I 
compare the brightness of different 15 degree beamwidth types as emitters
at the same current.  There is a huge variation !  Even within one type the
specs often allow a 3:1 variation in brightness.

73,
Steve VE3SMA