The rule that the dimmer follows to convert the control input (between 0% and 100%) to output voltage (again between 0% and 100%) - also known as the dimmer curve.
Larger Lighting Desks frequently allow you to set up the dimmer curve at the control side - this is often called the dimmer 'profile'. Some dimmer packs also have selectable laws. Particular care should be taken when using both desk and dimmers with selectable laws to ensure that the desired result is obtained.
If different control systems (analogue/DMX) or models of dimmer are being used together, it is frequently necessary to check that all are operating with the same law.
On older analogue dimmers, this is the way the output curve looks as a result of phase control on a sinewave (how all leading edge triac dimmers work) if no correction is applied to the control input. Note that, at 50% control input, the output is also at 50%. Historically, the majority of dimmers followed this law as other laws required additional circuitry.
Square is usually for Video Cameras, which are more sensitive than the human eye to variations in intensity at high light levels. The square law is intended to compensate for the response curve of the camera, so that the brightness as seen by the camera varies linearly with the control input.
Switch or non-dim keeps the output at 0 until the control passes a set point (normally 50%), where the output then snaps to full.
Be careful with terminology - different manufacturers have different conventions for describing laws.
- Table and graph showing control setting percentage (post dimmer law) against colour temperature and percentage of current used