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A color wheel or other switch for changing a projected 
A color wheel or other switch for changing a projected hue
In color theory, hue is one of the main properties (called color appearance parameters) of a color, defined technically in the CIECAM02 model as "the degree to which a stimulus can be described as similar to or different from stimuli that ...
(e.g., for an optical display) is a device that uses different optics filters or color gel
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associa ...
s within a light beam
A light beam or beam of light is a directional projection of light energy radiating from a light source. Sunlight forms a light beam (a sunbeam) when filtered through media such as clouds, foliage, or windows. To artificially produce a light ...
. Common usage includes continuously-rotating wheels for seasonal home displays (e.g., at Christmas
Christmas is an annual festival commemorating the birth of Jesus Christ, observed primarily on December 25 as a religious and cultural celebration among billions of people around the world. A feast central to the Christian liturgical year ...
) and controllable color wheels for a particular instrument (e.g., SeaChanger Color Engine
The SeaChanger Color Engine is an electro-mechanical device that is used to control light color in entertainment-industry lighting applications. The unit employs four overlapped color filter wheels, inserted into a light beam near its source, to ...
for stage lighting
Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts.
), while non-wheel devices include scrollers and semaphore types with lever arms (e.g., on the 1897-1917 Grand Army Plaza fountain).
References
External links
* {{optics-stub Mechanisms (engineering) Optical filters