Infrared cut-off filter

They are often used in devices with bright incandescent light bulbs (such as slide and overhead projectors) to prevent unwanted heating.

These filters typically have a blue hue to them as they also sometimes block some of the light from the longer red wavelengths.

Such filter stock is most easily made available most simply by having any commercial color negative film developed after being fully exposed to light.

(Some special communication may be necessary in such submission, to ensure that all of the "black" negative film thus produced is indeed returned, and that there is no need to print the color-negative results on photographic paper).

In the same way, visually opaque "black" color-positive film emulsions mounted in cardboard, as for routine slide projection, provide inexpensive cardboard-mounted infrared filters.