A quantifiable measure of how impenetrable a substance is to visible light or other electromagnetic radiation. It is the inverse of transmittance. In lighting and optics, specifying opacity is critical for designing diffusers, gels, and gobos, determining exactly how much luminous flux will be absorbed or reflected rather than passing through.
Heard on the job
The client wants total blackout curtains, so we need a fabric with 100 percent opacity.
Related terms
Absorptance
The ratio of absorbed radiant flux to the total incident radiant flux on a surface.
Haze
A fine, even mist pumped into the air so that light beams become visible on stage or on set.
Luminous flux
The total amount of visible light a source emits in all directions, weighted for the eye's sensitivity and measured in lumens.