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Backstage world - resources for light equipment

Principles of lighting

There are many general principles to lighting a stage, although to allow for artistic effect, no hard and fast rules can ever be applied. The principles of lighting include:

• Illumination: The simple ability to see what is occurring onstage. Any lighting design will be ineffective if the audience has to strain to see the characters; unless this is the explicit intent.

• 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. Harsh red light has a totally different effect than soft lavender light.

• Location and time of day: Establishing or altering position in time and space. Blues can suggest night time while orange and red can suggest a sunrise or sunset. Use of gobos to project sky scene, moon etc

• 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.

• Selective visibility: Lighting may be used to show only the areas of the stage which the designer wants the audience to see.

Qualities of lighting

In the pursuit of these principles, 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 lamp, 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 it is 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 or amber shift. 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 lamp, 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) and their derivatives (see below), 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 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 come in many shapes, but often include leaves, waves, stars and similar patterns.

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 disadvantges 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 intertial 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 to 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.

Lighting instruments

In the context of lighting design, a lighting instrument is a device that produces controlled lighting as part of the effects a lighting designer brings to a show. A lighting instrument is different from a “light” in much the same way that a musical instrument is different from a “music”.

There are a variety of instruments frequently used in the theater. Although they vary in many ways they all have the following four basic components in one form or other:

• Box/Housing - a metal or plastic container to house the whole instrument and prevent light from spilling in unwanted directions.
• Light Source (bulb or lamp).
• Lens or opening - the gap in the housing where the light is intended to come out.
• Reflector - behind or around the light source in such a way as to direct more light towards the lens or opening.

Additional features will vary depend on the exact type of fixture.

Most theatrical light bulbs (or lamps, the term usually preferred) are Tungsten-Halogen (or Quartz-Halogen), an improvement on the original incandescent design that uses a halogen gas instead of an inert gas to increase lamp life and output. Fluorescent lights are rarely used other than as work lights because, although they are far more efficient, they cannot be dimmed (run at less than full power) without using specialised dimmers and they will not dim to very low levels. They also do not produce light from a single point or easily concentrated area, and have a warm-up period, during which they emit no light or do so intermittently. High-intensity discharge lamps (or HID lamps), however, are now common where a very bright light output is required, - for example in large follow spots and modern automated fixtures. When dimming is required, it is done by mechanical dousers, as these types of lamps cannot be electrically dimmed.

Most instruments are suspended or supported by a "U" shaped yoke, or 'trunion arm' fixed to the sides of the instrument, normally near its center of gravity. On the end of such, a clamp is normally fixed, made in a "C" configuration with a screw to lock the instrument onto the pipe or batten from which it is typically hung. Once secured, the fixture can be panned and tilted using tension adjustment knobs on the yoke and clamp. An adjustable wrench/spanner is sometimes used to assist the operator in adjusting the fixture.

All lights are classified as either floodlights (wash lights) or spotlights. The distinction has to do with the degree to which one is able to control the shape and quality of the light produced by the instrument, with spotlights being controllable, sometimes to an extremely precise degree, and floodlights being completely uncontrollable. Instruments that fall somewhere in the middle of the spectrum can be classified as either a spot or a flood, depending on the type of instrument and how it is used. In general, spotlights have lenses while floodlights are lensless, although this is not always the case.

Please note: In the UK the nomenclature is slightly different from North America. This article primarily uses the North American terminology. Although there is some adoption of the former naming conventions it has been normal to categorise lanterns by their lens type, so that what in the US is known as a spotlight is known as a Profile or a Fresnel/PC (Pebble/Plano/Prism Convex) in the UK. A Spotlight in the UK often refers to a Followspot. The following definitions are from a North American point of view, and would be confusing when used, without further clarification, in the UK. UK naming conventions are considered to be correct in most of the world, in fact most North American theatres will also use the UK terms except when talking in a more general sense (ie get a spotlight to focus on xxx, or 'flood this area')

Also note: In Australia and many other places, the lamps inside a theatrical fixture are referred to as bubbles. In North American English, 'bubble' refers to the protrusion that occurs when one's body (or other oily substance) contacts the lamp. Oil will cause the portion of the lamp which has oil on it to expand when it is on (lamps generate a lot of heat), creating the 'bubble', and causing the lamp to explode. That is why one should never directly touch the glass portion of a lamp. Cleaning with rubbing alcohol will nuetralize the oil.

Lighting controls

Lighting control tools might best be described as anything that changes the quality of the light. Historically this has been done by the use of intensity control. Technological advancements have made intensity control relatively simple. Solid state dimmers can be controlled from multiple sites, or by a computer controlled by lighting desks connected to dimmers and, in the case of luminaires and other remotely-controllable fixtures, directly using 5-pin cable carrying the DMX protocol. Control has grown to the point of total automation of the entire show through show control once lighting and other designs have been completed and programmed.

The dimmer is the device used to vary the voltage to the instrument’s lamp. As voltage to the lamp decreases, the light fades or dims. It is important to note that some color change also occurs as a lamp is dimmed, allowing for a limited amount of color control through the dimmer. Fades can be either UP or DOWN, that is increasing or decreasing the intensity. Today, most dimmers are solid state, although many mechanical dimmers still exist.

With the increased use of computers and DMX protocol, lighting control has grown to include not only the change in a light’s intensity, but the movement and color of the light, as well as the pattern.

Other modern control methods include RDM (Remote Device Management) which implements the type of control available with DMX into a network topology run over Cat5 Network Cabling. This allows the possibility of feedback from units of faults etc, whilst allowing much more detailed control of them.