Another LED nut, Craig Johnson (LED Museum), has a web page on
infrared
LEDs, including some photos taken with digital cameras. He shows
several diferent wavelengths of IR LEDs, and the funny colors they
appear to the digital cameras that he used.
http://ledmuseum.home.att.net/ledir.htm
This is quite fascinating. I discovered several years ago that IR LEDs
in remote controls could be "seen" by our camcorders. Our current one
is especially sensitive when switched into "NightShot" mode, because
that's how it's designed--it uses IR LEDs which are mainly invisible
(except for the dim red glow I notice when they're on that I don't see
with ordinary remote LEDs) to allows shooting (black-and-white) images
even in complete darkness.
I've had interesting results looking at ordinary objects with NightShot
mode turned on. I assume that NightShot mode switches it into a
special mode where it effectively becomes an IR camera. The most
obvious is that red and white objects look nearly the same shade, so
red text on a white background (or vice-versa) become nearly invisible,
which makes sense because IR is close to red in the spectrum. I've
found some objects that appear dark in visible light but look very
bright with NightShot on. I've seen a dim gray background on the
vacuum-fluorescent display of a stereo system we had in the past that
didn't show up to my eyes (probably produced by the IR of the heating
filaments?). Before looking at the IR filter on a remote control, I
guessed that it would look clear in this mode since I knew the filter
was designed to block most visible light but pass IR, and I was
right--I turned on NightShot mode while looking through the viewfinder,
and I could instantly see right through all of these filters as if they
were crystal-clear.
It turns out, my digital camera has enough sensitivity to IR to
render
off-color (magenta-ish) glowing coals in a fireplace!
Last Independence Day I noticed something odd like this--a firework that
had just gone out seemed fuzzy and looked as if it was glowing a very
odd dim white color when I looked at it through the viewfinder (I was
not in NightShot mode, just ordinary visible-light color mode), and I
didn't see this color through my other eye which was not looking
through the viewfinder. It must have been the IR emitted by it.