Dimming

A dimmer is a device used to vary the average voltage applied to an instrument's lamp. The brightness of a lamp is proportional to its electric current, which in turn is proportional to the applied lamp voltage. When the applied voltage is decreased, a lamp's electric current will also decrease, thus reducing the light output from the lamp (dimming it). Conversely, a higher voltage will cause higher lamp current and increased (brighter) light output. Dimmers are frequently found in large racks that draw significant three-phase electrical power. They are often removable modules that range from 20-ampere, 2.4-kilowatt to 100-ampere units.

In the case of incandescent lamps, some color changes occur as a lamp is dimmed, allowing for a limited amount of color control through a dimmer. Fades (brightness transitions) can be either UP or DOWN, meaning that the light output is increasing or decreasing during the transition. Most modern dimmers are solid state, though many mechanical dimmers are still in operation.

In many cases, a dimmer can be replaced by a constant power module (CPM), which is typically a 20- or 50-ampere breaker in a dimming module casing. CPMs are used to supply line voltage to non-dimming electrical devices such as smoke machines, chain winches, and scenic motors that require constant operating voltage. When a device is powered by a CPM, it is fully energized whenever the CPM is turned on, independent of lighting console levels. CPMs must be used (in lieu of dimmers) to power non-dimming devices that require specific line voltages (e.g., in the US, 110 V, 60 Hz power) in order to avoid damage to such devices. Dimmers are seldom used to control non-dimming devices because even if a dimmer channel is trusted to always operate at full power, it may not be controlled when communications are disrupted by start up and shut down of the lighting control surface, noise interference, or DMX disconnects or failure. Such a loss of control might cause a dimmer to dim a circuit and thus potentially damage its non-dimming device.

Increasingly, modern lighting instruments are available which allow remote control of effects other than light intensity, including direction, color, beam shape, projected image, and beam angle. The ability to move an instrument ever more quickly and quietly is an industry goal. Some automated lights have built-in dimming and so are connected directly to the control cable or network and are independent of external dimmers.