Red is used because the rod cells, that are used for night vision, down
to a point where they are almost quantum limited
<https://www.cns.nyu.edu/csh/csh04/Articles/Rieke1998.pdf>, have a peak
sensitivity for greenish blue, but are very insensitive to very deep
reds, whilst they retain some sensitivity to the high frequency limit of
the blue cone cells. Night vision doesn't have the same spectral
response as a monochrome camera.
Light of a colour to which they are sensitive bleaches the sensor
pigment, reducing sensitivity.
Ideally, you don't want to use the brightest red LEDs, but rather those
with the longest wavelength consistent with an adequate remaining cone
cell sensitivity.
See <https://midimagic.sgc-hosting.com/huvision.htm> for typical colour
sensitivity curves.
--
David Woolley
On 16/10/2020 14:31, Ken B wrote:
Why do you use red and not blue or green
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