Color gels or color filters also known as lighting gels or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to color light and for color correction. Modern gels are thin sheets of polycarbonate or polyester, placed in front of a lighting fixture in the path of the beam. Gels have a limited life, especially in saturated colors. The color will fade or even melt, depending upon the energy absorption of the color, and the sheet will have to be replaced from time to time
A diffusion filter is a translucent filter used for special effect lighting. Diffusion filters are also used in stage lighting where they may also be called diffusion gel, or just diffusion. Diffusion gels or filters soften the light in order to reduce or diffuse shadows or glare or can change the beam angle or beam spread (light shaping) to wash an area with light more effectively.