Modern stage lighting is a flexible tool in the production of theatre, dance, opera and other performance arts. Several different types of lighting instrument are used in the pursuit of the various principles or goals of lighting. These Principles of Lighting include:
- Illumination: The simple ability to see what is occurring onstage.
- Revelation of Form: Altering the perception of shapes onstage, particularly three-dimensional stage elements.
- Focus: Directing the audience's attention to an area of the stage or distracting them from another.
- Mood: Setting the tone of a scene.
- Location and Time of Day: Establishing or altering position in time and space.
- Projection/Stage Elements: Lighting may be used to project scenery or to act as scenery onstage.
- Plot: A lighting event may trigger or advance the action onstage.
In the pursuit of the Principles of Lighting, the three main Qualities or Properties of interest are:
- Intensity: Measured in both lux and lumens. For any given luminaire (lighting instrument or fixture), this depends upon the power of the bulb, the design of the instrument (and its corresponding efficiency), the presence or absence of color gels or gobos, distance from the area to be lit, the color and subtance to be lit, and the neuro-optics of the total scene (that is, the relative contrasts to other regions of illumination).
- Color: Color temperature is measured in kelvin, and gel colors are organized by several different systems maintained by the color manufacturing companies. The apparent color of a light is determined largely by the gel color given it, but also in part by the power level the lamp is being run at and the color of material is it to light. As the percentage of full power a lamp is being run at drops, the tungsten filament in the bulb glows orange instead of more nearly white. This is known as Amber Drift. Thus a 1000-watt instrument at 50% will appear far more orange than a 500-watt instrument at full.
- Pattern: Pattern 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 the bulb, reflector and lens assembly. Different mounting positions for the bulb (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) and their derivatives, 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 ERS's and similar lamps. This is typically a strip of metal with a shape cut into it. It is inserted into the lamp near its aperture. Gobos come in many shapes, but often include leaves, waves, stars and similar patterns.
In addition to these, certain modern instruments are 'movable' (AKA: 'intelligent'), referring to motorized movement of either the entire lamp or a mirror placed in front of its outermost lens. These lamps and the more traditional follow spots add Direction to the relevant characterists of light.
It is important to note that 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.
The above elements of lighting are primarily the domain of the lighting designer (LD). In consultation with the director and the scenic or stage designer and after watching sufficient late rehearsals, the LD is responsible for providing an Instrument Schedule and a Lighting Plot. The Schedule is a list of all required materials, including gel colors, gobos, color wheels, barndoors and other accessories. The lighting plot is typically a plan view of the theatre in which the performance will take place, with every luminaire marked, including its 'rough' focus (the direction it should be pointing), its instrument number, any color/gobo/accessories required, and the specifics of its connection to the lighting control systems (channel number). These form the basis of the work the Lighting Crew is to undertake, under the supervision of the Head Electrician and the direction of the Crew Chief.
There are a variety of instruments frequently used on the stage.
It is important to note that virtually all theatrical bulbs are incandescent. Fluorescent lights are rarely used outside of work lights because, although they are far more efficient, they cannot be 'dimmed' (run at less than full power), they do not produce light from a 'point' or easily concentrated area, and have a warm-up period, during which they emit no light or do so intermittently. Until recently (1990s), carbon arc lamps were common in high power follow spots. Carbon arc follow spots have been largely replaced by high-intensity xenon or halogen instruments.
All lights are either Floodlights or Spotlights. The distinction has nothing to do with the area covered, but is based upon the presence or absence of a focusing lens or lenses. Lamps that lack a focusing lens or are in a permanent fixed relationship to their lens are Floodlights.
PAR lights (parabolic aluminized reflector) These resemble car headlights. They possess a lens, but it is an integral part of the lamp housing, and its position relative to the filament cannot be altered.
The lamp produces an intense oval pool of light with soft edges. The only adjustment is a knob that allows the lamp unit to be rotated within its casing, thus changing the orientation of the oval.
These types of instruments come in varying diameters, the most common being designated PAR56 and PAR64 the number indicates the diameter of the housing in eighths of an inch (eg a PAR64 is eight inches in diameter).
The PAR's are used constantly in Rock and Roll shows, especially in combination with smoke/hazer machines which make the path of the beam visible. Because of the lack of control over the beam diameter, shape, and sharpness the PAR's are rarely used in a FOH (front of house, the lighting position suspended over the audience) position, but are used often as top light and for special effects.
Strip or Cyclorama (Cyc) lights These are long housings typically containing multiple bulbs arranged along the length of the instrument and emitting light perpendicular to its length. The strip light housing often contains bulbs of multiple colors (usually the primary colors) with each color controlled by a separate electrical circuit. Varying the intensity of the different colors enables the lighting designer to establish mood or time of day.
Scoops These are circular fixtures that do not have any lenses. They have a reflector at the back of the fixture that directs the light out of the fixture. Since they do not have any sort of lens system they are cheaper then other fixtures. However, the downside of this makes it so that you can not focus the light at all (even the PAR's allow for more control then the Scoops).
House lights and Work lights House lights are incandescent or fluorescent floodlights. House lights provide light for the audience before and after performances and during intermissions. Work lights provide general lighting backstage, or in the house. House lights are often controlled by dimmers, but are sometimes on simple switches. Work lights are almost always switched only. House and work lights are usually off during performances but are occasionally included in the lighting design to establish focus or emphasize plot elements.
- Ellipsodial Reflector Spotlights
Fresnel: Fresnels are typically 6 or 4 inch, referring to the diameter of the lens. The lens is the distinctive 'Fresnel lens' type, with a 'stepped' appearance instead of the 'full' or 'smooth' appearance of other lenses. The stepped nature of the lens causes a corresponding pattern of circles of light, so Fresnel lenses are usually 'stippled' on the flat side. This pattern of small bumps helps to break up the light passing into the lens to smooth out its eventual pattern.
Fresnels use a parabolic reflector, with the filament of the bulb at the focus. Due to this, the bulb and reflector cannot move independently of one another, and remain a fixed unit inside the housing. It is this unit that is moved back and forth inside the lamp to focus the fresnel. This is done by a slider on the bottom of the light, or by a worm track.
Fresnels are not very efficient. The reflector cannot be larger than then lens aperture, and thus all the radiated light that is neither reflected by the parabola behind the bulb or emitted directly through the lens is absorbed by the casing as waste heat. Additionally, the degree to which the lamp may be focused is limited by the length of the housing. The tighter the focus ('spotted in') the less light is able to escape. Thus fresnels are not good for tight focus on small areas. Fresnels also lack internal shutters, and must rely on barndoors, large metal flaps that may be mounted just beyond the color slot at the front of the light. Due to these restrictions, Fresnels are most often used at middling distances for area lighting. Fresnel bulbs are almost always 'base down': mounted with the bulb up.
ERS: The Ellipsoidal Reflector Spotlight is also sometimes known as a 'Leko'. It comes in very many forms, and is the most numerous and important instrument type in use. The flexibility of the ERS allows them to fulfill the bulk of the lighting roles in the theatre, from area lighting to close specials, from long throws from the back of the house to shin kickers on the stage.
ERSs may have more than one focusing lens, while all possess internal shutters for cropping the emitted light, and all accept a color gel in front of the lens and a gobo in front of the shutters. ERS's may have bulbs mounted axially, or with the base either up or down (it is important to hang a lamp in the proper orientation). The lenses are smooth and full, not stepped, and it is the lens or lenses that move in the ERS, not the bulb and reflector assembly as in the Fresnel.
The ERS improves over the efficiency of the Fresnel by surrounding the bulb in an ellipsoidal reflector, with the filament of the bulb at one focus and the aperture to the lens housing at the other. The shutters and gobo are ideally in focal point of this apature.
Moving lights or Intelligent fixtures: While originally implemented in 1972, the first computer-controlled stage lighting fixtures, called Moving Lights or Intelligent Fixtures, began to gain widespread acceptance in the Concert Industry in the early 1980's. As the digital age progressed, the cost of these fixtures was reduced and they slowly started being used in a more 'traditional' theatrical environment. Intelligent Fixtures are currently used in almost all major theatrical productions.
Usually relying on compact Arc lamps as a light source, these fixtures generally use stepper motors connected to varying internal devices to manipulate the light before it escapes the fixtures front lens.
Examples of internal devices are:
- Color wheels with dichroic lenses used to change the color of the beam.
- Pattern wheels with gobos used to change the shape of the beam.
- Shutters used to 'dim' or 'strobe' the output
- Automated lens trains used to focus the beam.
- Irises used to change the size of the beam.
- Gate shutters to 'square off' the beam.
- CYM Color-Mixing Wheels using Color-Subtraction technology to vary beam color.
The majority of these fixtures also use stepper motors to enable movement of the light fixtures output by either moving a mirror which reflects the beam, or by moving the entire fixture lens train. This allows the fixture to cover large areas by varying the X-Y coordinates of the beam. Higher performance fixtures use servo controlled motors for pan and tilt motion.
Moving Lights are controlled in many ways. Usually the fixtures are connected to a Lighting Console, which outputs a control signal. This control signal sends data to the fixture in a usually one of three ways - Analog (which has largely been phased out), DMX (which is the industry standard control protocol), or Ethernet Control (which is still in development). The fixture then takes this signal and translates it into internal signals which are sent to the many stepper motors located inside.
Theatrical lighting fixtures are controlled by lighting desks connected to dimmers and, in the case of luminaires and other remotely-controllable fixtures, directly using 5-pin cable through which the DMX protocol is often used.