1. A piece of coated transparent material intended to go in a lighting fixture to extend the life of any color media. Heat Shield is placed in the beam of the fixture between the lens and color media, and absorbs infra-red energy, therefore reducing infra-red heat at the color filter, while still outputting around 80% of the light. Versions are available from each of the "big four" color companies: Rosco, Lee, GAM, and Apollo. One often overlooked caveat: There must be airspace between the shield and the color. Double color runners as found on SourceFour ERS, S4-PAR, and PARnel is not enough.
Heat shield is often called gel shield, although Apollo's Gel Shield is a somewhat different product, stiffer and more expensive than others, but performs better also, because it reflects rather than absorbs the unwanted energy.
2. May also refer to a Zetex border, hung on an electric batten to prevent hot lights from contacting adjacent scenery or drapes.