An infrared beam has the capability of showing a wavelength of the spectrum that is normally invisible to the human eye. You can make your own IR flashlight by using a few household tools and adapting the light output of an ordinary incandescent bulb flashlight with exposed colour negative film. Your IR flashlight might not look as fancy as one purchased from a hobby store, but it will provide a beam of IR light just as well as any commercial model.
Buy a 2 1/4 by 2 /4 inch roll of colour negative film. Give it back to the photo shop developing centre where it was purchased to have it developed.
Put four strips of the colour negative film on top of each other so that the translucent sections line up.
Place a piece of printer paper on a table. Put a strip of the colour negative film down on the paper horizontally. Put three more strips of colour negative film down on the first strip horizontally.
Tape the ends and sides of the strips of colour negative film to the paper with cellophane tape.
Unscrew the reflector off of the small flashlight. Remove the plastic lens from inside of the back end of the reflector.
Place the back end of the reflector down on the colour negative film. Cut around the back end of the reflector and through the colour negative film with the utility knife.
Place the cut circles of colour negative film that have just been cut out inside of the back end of the reflector. Screw the reflector back onto the flashlight. You can now turn on your IR flashlight.
You can buy outdated photographic colour negative film in a discount bin at a photo or hobby store.
Do not touch the surface of the colour negative film as fingerprints will cloud its use.