Natural Science Forum / Physics / Optics / May 2005

IR (infrared) diode lights are easy to get and should serve your purpose.

KDS

The spectral sensitivity of your typical CCD extends well into the infrared
(google it) up to about 1um.  Because images with a full spectrum CCD
include the IR, they look strange to the human eye.  Consequently, all CCD
cameras have an included IR filter.  "Night vision" cameras swing the filter
out of the way.  However, since IR passes through polyester and Lycra
easily, there was a huge commotion a decade ago when people used IR pass
filters on their CCD cameras and took shots of women in black dresses that
looked like they were wearing only very shear langerie. Consequently, most
night vision cameras won't let you narrow the aperture or increase shutter
speed so use in night mode during daylight is impossible.  If your camera
doesn't say "night mode" then you can't get the IR filter to move out of the
way.

I've been having fun with this lately - you can cut out the back of most
webcam lense systems and break out the IR filter (looks like red coated
glass).  Then cover the back of the system with 2 layers of exposed color
negative film (this passes IR and blocks most visible light).  (trick - use
Elmers glue to fix in place - it passes IR)  Now for fun, look at the back
of a $20 bill with the webcam - a stripe of the image just disappears!
Pretty cool.

The IR LED's come in near IR (still somewhat visible to the human eye) and
beyond up to about 950 nm.  They are hard to work with unless you remember
that the voltage drop across the IR LED is only about 1.3 volts, so it can
draw twice the current that a red LED does and fry itself iif you swap it
into your typical LED circuit.

Have fun
Lyle