Dimming by gradually shielding the light has been in use long before the advent of electricity. With the increasing use of luminaires with discharge lamps, mechanical dimming has found new life. Discharge lamps require a constant direct current, and therefore cannot be controlled by changing the electric voltage, as with electronic dimmers.
A number of new forms of
mechanical dimmer
have been developed. These modern motorized mechanical dimmers , sometimes called dowsers or dousers, are usually controlled by the
lighting control
board. The most common
mechanical dimmer
works like venetian blinds, with slats which are opened and closed by a motor or manually. The dimmer is placed at the front of the luminaire.
A 17 century mechanical dimmer
Another method of mechanical dimming employs a linear
mechanical dimmer
incorporated into the
optical system
of the luminaire, which dims the light as its
aperture
closes. This type of dimmer is common in moving lights.
A different approach to the problem of mechanical dimming is evident in the design of changeable density mechanical dimmers. These scroll a strip of density filter which gradually changes from
clear
to black or from one color to another. These dimmers can be used either internally, incorporated into the luminaire, or as an add-on to the unit.
