Qualities in lighting

The four main qualities or properties of lighting are intensity, color, direction and focus.

Intensity

Intensity is measured in lux, lumens 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 color gels or mechanical filters, the distance to the area to be lit and the beam or field angle of the fixture, the color and material to be lit, and the relative contrasts to other regions of illumination.

Color

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

A tungsten lamp's color is typically controlled by inserting one or more gels 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 colors are obtained by means of subtractive CMY color mixing, by inserting combinations of cyan, magenta and yellow dichroic 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 colors. This creates custom colors 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" color correction) filter to extend the range (gamut) of subtractive color mixing systems,

Lamp power also influences color 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 color through additive color 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 cycloramalights.

Direction

Direction refers to the shape, quality and evenness of a lamp's output. The pattern of light an instrument makes is largely determined by three factors. The first are the specifics of thelamp, reflector and lens assembly. Different mounting positions for the lamp (axial, base up, base down), different sizes and shapes of reflector and the nature of the lens (or lenses) being used can all affect the pattern of light. Secondly, the specifics of how the lamp is focused affect its pattern. In ellipsoidal reflector spotlights(ERS) or profile spotlights, there are two beams of light emitted from the lamp. When the cones of both intersect at the throw distance (the distance to the stage), the lamp has a sharply defined 'hard' edge. When the two cones do not intersect at that distance, the edge is fuzzy and 'soft'. Depending on which beam (direct or reflected) is outside the other, the pattern may be 'thin and soft' or 'fat and soft.' Lastly, a gobo or break up pattern may be applied to ERSs and similar instruments. This is typically a thin sheet of metal with a shape cut into it. It is inserted into the instrument near its aperture. Gobos, or templates, come in many shapes, but often include leaves, waves, stars and similar patterns.

Focus, position, and hanging

Focus is a term usually used to describe where an instrument is pointed. The final focus should place the "hot spot" of the beam at the actor's head level when standing at the centre of the instrument's assigned "focus area" on the stage. Position refers to the location of an instrument in the theater's fly system or on permanent pipes in front-of-house locations. Hanging is the act of placing the instrument in its assigned position.

In addition to these, certain modern instruments are automated, referring to motorized movement of either the entire fixture body or the movement of a mirror placed in front of its outermost lens. These fixtures and the more traditional follow spots add direction and motion to the relevant characteristics of light. Automated fixtures fall into either the "moving head" or "moving mirror/scanner" category. Scanners have a body which contains the lamp, PCBs, transformer, and effects (color, gobo, iris etc.) devices. A mirror is panned and tilted in the desired position by pan and tilt motors, thereby causing the light beam to move. Moving head fixtures have the effects and lamp assembly inside the head with transformers and other electronics in the base or external ballast. There are advantages and disadvantages to both. Scanners are typically faster and less costly than moving head units but have a narrower range of movement. Moving head fixtures have a much larger range of movement as well as a more natural inertial movement but are typically more expensive.

The above characteristics are not always static, and it is frequently the variation in these characteristics that is used in achieving the goals of lighting.

Stanley McCandless was perhaps the first to define controllable qualities of light used in theater. In A Method for Lighting the Stage, McCandless discusses color, distribution, intensity and movement as the qualities that can be manipulated by a lighting designer to achieve the desired visual, emotional and thematic look on stage. The McCandless Method, outlined in that book, is widely embraced today. The method involves lighting an object on the stage from three angles — 2 lights at 45 degrees to the left and right, and one at 90 degrees (perpendicular to the front of the object).