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.