I have never found any economy in building what I can buy. Just takes
to much time. You can buy inexpensive IR gells from which you can cut
out what you need. Look for a low pass gell at about 750nm. A cheep way
is to process a sheet of unexposed slide film if you need a large piece.
Or take some of the ends from a processed roll of 35mm or 120 slide
film. You can layer them if you need it darker to visable light.
Performance wise though, it is going to be hard to beat a real IR
illuminator like what is use on night vision devices. Oh by the way,
all CCD sensors are sensitive to IR (down to 1300nm) light. All you
need to do is to remove the camera's high pass filter and replace it
with a clear to IR glass. I have been playing around with a CCD digital
camera with a Hoya R72 (720nm low pass) It is an Olympus 2020 and I am
comparing it to Kodak HIE film with the same filter. The film is about
5 stops faster than the digital sensor.

Don Bruder wrote:

Some of you may recall my post a few weeks ago asking about IR LEDs,
filters, and other yakkety-yak about cheap ways to fab a light source
that puts out either pure IR, or "close enough to it", with little or no
visible component, for use in what boils down to a homebrew "Night
Vision" system designed around a video camera that has a
well-demonstrated sensitivity to IR in the same region of the spectrum
that TV remotes use.