What are plastic sheets placed over lights to change their color called?

Plastic sheets placed over lights to change their color are known as gels. Gels are specifically designed to alter the color of the light emitted from the source, providing filmmakers and photographers with the ability to create mood, contrast, and thematic elements in their projects. They can be used in various applications, from color correction to achieving creative lighting effects.

Additionally, gels are available in a wide range of colors, allowing for significant versatility in lighting design. This tool is vital in the audio, video, technology, and film industry to ensure that the visual output aligns with the intended artistic vision. Their primary function is to soften or shift the color temperature of the light rather than diffuse the light or reflect it, which is different from the roles performed by diffusers, filters, and reflectors.