Stage lighting Qualities in Lighting

- Aug 17, 2017 -

Intensity

An example of a rig including moving head, generic and LED fixtures at 'The Tuesday Club'

Intensity is measured in luxlumens and foot-candles. The intensity of a luminaire (lighting instrument or fixture) depends on a number of factors including its lamp power, the design of the instrument (and its efficiency), optical obstructions such as colour gels or mechanical filters, the distance to the area to be lit and the beam or field angle of the fixture, the colour and material to be lit, and the relative contrasts to other regions of illumination.

Colour

Colour temperature is measured in kelvins. A light's apparent colour is determined by its lamp colour, the colour of any gels in the optical path, its power level, and the colour of the material it lights.

A tungsten lamp's colour is typically controlled by inserting one or more gels (filters) into its optical path. In the simplest case, a single gel is inserted into the optical path to produce light of the same color. For example, a blue gel is used to create blue light. Custom colours are obtained by means of subtractive CMY colour mixing, by inserting combinations of cyan, magenta and yellow filters into the optical path of the lighting fixture. The inserted filters may have varying densities, with correspondingly varied percentages of transmission, that subtractively mix colours. This creates custom colours in a manner similar to ink jet printers, which mix varied densities of cyan, magenta and yellow inks. Manufacturers will sometimes include an additional green or amber ("CTO" colour correction) filter to extend the range (gamut) of subtractive colour mixing systems,

Lamp power also influences colour in tungsten lamps. As the lamp power is decreased, the tungsten filament in a bulb will tend to produce increasing percentages of orange light, as compared to the nearly white light emitted at full power. This is known as amber drift or amber shift. Thus a 1000-watt instrument at 50 percent power will emit a higher percentage of orange light than a 500-watt instrument operating at full power.

LED fixtures create colour through additive colour mixing with red, green, blue, and in some cases amber, LEDs at different intensities. This type of color mixing is often used with borderlights and cyclorama lights.


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