The first question we have to ask is what we need lighting to do. This is a fairly basic process but one which must be remembered when one is using lights and building a lighting plan.

Lights are used to:

• Enable the audience to see the performers
• Enable the audience to see the set
• Create a mood
• Inform the audience of part of the story and scene
• Light the audience

In the beginning, there were candles, and not much else. They were a fire hazard and what little light they did produce was extremely yellow. Eventually, people began to burn quicklime, producing more light (although this was fairly green in colour).
Gaslights were more reliable, easier to control but even they were not very flexible and still meant burning stuff in a theatre full of people; not particularly safe.
In 1879, Thomas Edison and Joseph Swan demonstrated the first effective filament lamps to the world. The process was simple: pass an electrical current through a very thin metal wire, encase it in an oxygenless environment to prevent it from oxidising and wait for the wire to heat up to a temperature at which it emits light. Most theatre lamps still use this process although other methods of light emission are used for more expensive lights.

Assuming we use a filament lamp, we need to know a little about the way it produces light. The electricity passing through it is solely to heat the metal filament up; it is the temperature of the metal which is all-important.
As the metal's temperature increases, it starts to emit infra-red, then red, orange, yellow, blue and finally white. A hot filament will produce a small amount of orange light, giving the light beam from the light a dull orangey red appearance. A very hot filament will produce lots of red, orange as well as all the other colours in the visible spectrum, giving the appearance of a bright white beam.
Ordinary house lights (~60W) run at relatively low temperatures, giving a fairly dark, yellowy light. Theatre lights (~500W-1kW) run at higher temperatures, giving bright, slightly yellow beam whilst lights such as Par64s (1kW) run at even higher temperatures and produce a very bright, white beam. The important things to remember are that different lights produce light of different colours and intensities and as you dim any light, it will start to produce a more orangey beam.

• Filament: bit of thin metal which is heated up by an electrical current, producing light in all directions
• Reflector: a reflective surface which directs light in a particular direction. The reflector can be any shape but the most common cross-sections are circular or oval to form the light rays emitted from the filament into a beam of light.
• Lens: a shaped piece of glass to redirect the light rays as they pass through. Although most lights use a normal curved (plano-convex) lens to produce an accurate image, these lenses tend to be thick and so heavy. The other option is the Fresnel lens which uses a series of concentric rings of glass to focus the light, enabling a light but powerful lens to be produce.
• Shutters: a series of metal plates that can be used in some lights to shape the light beam emitted. With the shutters fully retracted, the beam is circular but with them pushed in, the light beam can be square or rectangular.
• Barndoors: a set of flaps that can be used on some lights to restrict the light emitted. They act like shutters but are not as precise and are generally used to stop spilled light.
• Gobo: A gobo is a piece of metal (or in some cases, glass) which can be placed inside some lights to block out parts of the light. This sillouette is projected as a shape of light and so allows patterns of light to be formed. Many hundreds of gobos are available in standard patterns, logos, text and shapes and they can also be custom produced if required.
• Gel (or colour filter): White light may show what is happening on stage but it doesn't really create a mood and gets a bit boring after a while. Gel is a coloured sheet of plastic which is fixed to the front of a light inside a gel frame and which produces a coloured light beam. Like gobos, there is a vast number of standard gel types made by a number of companies. Here's a rough guide to their effects:

• Red: angry, dramatic
• Blue: cold, night time
• Pale purple: neutral
• Orange/yellow: warm
• Dark colours are usually used for lighting bands and since they absorb lots of light, they can get very warm and eventually melt.
• Paler colours are more suited to theatre lighting where subtle mood setting is required.

Fresnel
	A light which uses a circular reflector and which is named after the lens which it uses. The Fresnel lens is not very precise however and gives a very soft edged beam as well as spreading a great deal of light outside the beam (spill). The light can be focused in order to alter the size of the light beam but it cannot project gobo images. Despite being not particularly efficient, the Fresnel is a good light for stage lighting, especially at close & medium ranges to the subject.
Profile
	An efficient light which uses one or more lenses and an ellipsoidal reflector to focus the light into a sharp beam. They usually have a longer body than Fresnel and can be focused to form a sharp circular beam with little spill. This sharp beam enables the light to project gobos as well as using shutters to project a specifically shaped light beam. Most profiles have a fixed beam angle although zoom profiles are available, giving an adjustable beam size. Profiles are suited to projections and for lighting at medium and long ranges from the subject.
PC (Pebble Convex)(Plano-Convex)
	A cross between a Fresnel and a Profile which uses a rough reflector to diffuse the light, producing a beam which is similar to an out of focus Profile. The PC is more efficient than a Fresnel and also produces less spill.
Flood
	An uncontrolled light which produces a very large area of illumination. It has no lens and relies on a large reflector to direct the light out, resulting in a cheap and efficient light which produces enormous amounts of spill. An asymmetric floodlight directs more light upwards and is used to light flat walls (or cycs). This means the part of the surface furthest away gets more light and so the wall is evenly lit. Floodlights are generally used to produce large colour washes.
Parcan
	This light is built around it sealed lamp, consisting of lens, filament and reflector. This arrangement produces an extremely robust bulb able to operate at high temperatures and for short flashes. The Parcan has a metal tube around the front of the bulb, giving a very cheap, powerful light which weighs little but produces a very bright, white light. The beam can't be focussed and is a soft ellipse with little definition. The Parcan is suited to a wide range of duties, most notably band lighting.

	From above: gives a very dramatic effect with very dark shadows showing little of the face.
	From the front: gives good illumination of the face but produces a very unnatural 2D effect.
	From the back: gives a silhouette effect, showing little detail of the person's face but giving a good indication of their posture and movement.
	From the back, front and both sides: gives a good overall effect with detail, natural shadows and an appearance of 3D. The lights should be at the correct levels (possible also using gel) to get the best results.

A light requires power and although it could be controlled with a simple light-switch, we usually want to be able to alter the intensity of the light. To do this, we need to use a dimmer which varies the amount of power sent to the light. The dimmers in theatres are built into rooms where they can operate safely, reliably and quietly. The dimmers are controlled remotely by a lighting desk. Working backwards in the chain:

• Light: receives power and emits light
• 15 amp cable: most lights are powered through a 15A cable. This is exactly the same as your normal 13A mains wiring except that the cable can carry more power and the sockets are a different round-pin design to ensure that only 15A plugs can fit 15A sockets.
• Multicore cable (named Lectroflex): The dimmers may be 50m from the dimmers and it should be obvious that its a bad idea to power 100+ lights by using an individual 50m cable for each light. To reduce the cost of this (and the effort of installing hundreds of long cables) multicore wiring is used. This carries 6 of the normal 15A cables in one cable and allows easier connection. At the light end, an adaptor is used to split the multicore cable up into 6 separate sockets.
• Dimmer: the dimmer sends a variable amount of power out to the light via the power cabling. Last century, the dimmers were controlled manually but today they are controlled remotely by lighting desks.
• Control cable (named DMX512 cable): When lighting desks were first used, each channel on the desk would send a voltage by a wire to its dimmer. A signal of 10V would direct the dimmer to turn the light fully on, a signal of 5V would indicate the light was to be at 50% output. This meant that for many lights, many channels would be used and so hundreds of control cable would be used.
  This was difficult to set up, expensive, unreliable and prone to interference so in the last ten years, a digital form of control began to be used. A single cable would be used to send the information of what level the channels were at and this could cope with controlling 512 channels. For more information, see our section on DMX.
• Lighting Desk: Simple desks consist of a series of faders that control a channel each and by using two sets of faders, the lighting controller can change from one state to another by using a crossfade control. Although this is simple, it is very time consuming and so modern desks use computer control to set up the lighting with each scene being saved into memory and then outputted as the lighting controller requires.

Credits:
The Backstage Basic Lighting Guide was written by Colin Hodges and is © BTS 2002.
No reproduction in whole or in part in any means whatsoever is permitted without written consent.