Lamp and Fixture Diffusers
Most general commercial lighting uses diffusers. These reduce surface brightness and disperse the light. In task lighting, the first function is useful, but the second is usually a disadvantage. Conventional diffuser material disperses light too widely for efficient task lighting, unless the task area is large or the fixtures are very close to the task.
In principle, surface brightness can be reduced to any desired level by increasing the diffuser area. The diffusers of typical fluorescent fixtures increase surface area and reduce the surface brightness by a factor of two to five, compared to the surface area of the bare tubes. This is usually adequate for most task lighting. Diffusing incandescent or HID task lighting requires some creativity. At present, there are no standard types of large-area diffusers for these sources. Custom fixtures can be fabricated using standard fixture components and diffuser materials.
Conventional diffuser materials used with fluorescent lighting absorb 30% (e.g., clear prismatic) to 50% (e.g., milky white) of the light produced by the lamps. Some diffuser materials, such as the typical shades of table lamps, are too absorptive for efficient lighting.