A colour scroller or colour changer is an electro-mechanical lighting accessory used in theater, film, dance and concerts to change the colour projected by stage lighting instruments without the need of a person to be in the vicinity of the light. A colour scroller moves plastic "gel" colour gel [actually dyed polyester and/or other base materials coated with dyes] into the beam of the light. It is generally attached to the gel frame holder at the transmitting end of a lighting fixture, so colour is introduced after the beam characteristics have been defined by the optics of the lighting instrument. Most scrollers are controlled via DMX512 protocol, but some models (e.g. Wybron's Colouram IT) also utilize the RDM protocol. When colour scrollers were first introduced around 1980, a number of companies produced them, including: Avolites, GAM Products, Morpheus Lights, Rainbow, Rosco Laboratories and Wybron Inc. Now the main manufacturers are: A.C. Lighting, Apollo, Morpheus Lights and Rainbow (in alphabetical order).
Types of scrollers
Single string scrollers
The most commonly used type of scroller is the single string scroller. This type has only one string of colour anywhere from 2 to 33 frames long.
Dual string scrollers
Dual string scrollers use 2 strings (one behind the other) and allow for a form of CMY mixing. The Apollo MXR 2, Chroma-Q Cascade and the Wybron CXI use 2 gel strings to obtain a CMY mix. One frame of clear gel is positioned at the center of each gel string (50% DMX) with progressively denser frames of colour positioned to either side of it. The first string has progressively denser yellow and cyan frames and the second string has progressively denser yellow and magenta frames. This permits various YC, YM, and CM combinations to be achieved as a "static" colour mix. There is a limited ability to transition "live" between mixed colours - although some transitions cannot be accomplished without passing through the clear center frame.
CYM colour-mixing scrollers
Finally, there are "true" CYM mixing scrollers that utilize three independently controlled gel strings - namely, the "ColorFader" system manufactured by Morpheus Lights of Las Vegas, NV, USA. Independent control of the gel strings permits users to cross-fade "from any color, to any color, anytime" directly (without going through undesired colours as on a single or double string colour changer).
The ColorFader system predated the dichroic systems used in most moving lights, to create smooth colour transitions. The basic concept of both systems is identical. Colour density variation is achieved by starting with a full-density sheet of gel (or dichroic glass) in either Cyan, Magenta or Yellow. The saturation of that colour is varied by perforating the gel sheet (or ablation of the dichroic) in a manner that permits unfiltered white light to pass through in varying amounts, progressing from full white to the fully saturated colour.
At the zero DMX "start" position on a ColorFader scroll there is a piece of clear gel (which is perforated with large holes to maximize light transmission). As the DMX control value is increased the gel string moves to the coloured gel, which has perforated holes are that are large and plentiful - so the percentage of white light passing through those hole predominates over that of the gel colour, and low-saturation colours are achieved. As DMX control value increases, it progresses the scroll further and the holes become smaller and less numerous - so the percentage of coloured material in the optical path increases relative to the white light pass-through, and the result is progressively higher density colour transmission. Ultimately, at full DMX, a solid, unperforated sheet of gel is positioned in the optical path - for full saturation.
Sizes
colour scrollers come in many different sizes and are mountable on nearly every type of conventional lighting instrument. Sizes include: 4 Inch (for smaller PAR 36 units) 6 to 7.5 Inch (fits ETC Source 4 19°, 26°, 36° and 50° units) 8 to 10 inch (fits PAR 56 & 64 units) 12 inch (fits large sized Fresnel units like 2 KW tungsten units) 15 inch (fits bigger Fresnels, like 5KW tungsten or 2.4 KW HMI units) 20-30 inch (fits Thomas 8 Light and Thomas 9 Light units) Large format scrollers for ETC Multi-PAR units