The term luminaire is used to describe a complete lighting unit. A luminaire comprises of an outer housing, which contains the reflector, lamp, and any lenses. The lamp and reflector combination produce a beam of light, which spreads from the front of the luminaire: this is called the beam angle.
Most luminaires use at least one lens, which is a piece of glass with one or both sides curved for concentrating or dispersing the light beam; this produces a variation in the beam angle and the quality of the light produced. The broad scope of luminaires can be sub-divided into various categories of unit, each of which has a specific job. These are explained in the following section.
The lamp is a glass (or quartz) envelope which contains a filament or electrodes surrounded by a gas. Lamps utilising an electrode arrangement are called discharge lamps. The type of gas and electrode arangement varies, giving rise to various lamp types. These are sumarised:
Some luminaires utilise an attachment on the front of the unit called a barndoor. This consists of four movable metal flaps which are used to control the spill of light produced. The barndoor is usually rotatable in relation to the luminaire, providing additional control.
Types of Luminaire
The many types of luminaire available can be classified in to one of the categories below. Each class of unit produces a different effect, and thus has a specific role to play. Categories are:
A luminaire with only a reflector to control the light output, thus giving a wide beam angle; there are no adjustments that can be made to the light beam. The purpose of a flood is to produce a soft even wash of light over a wide area. If required, barndoor attachments can be used to provide some degree of control over the spread of light.
Symetrical floods utilise an evenly curved reflector, producing an even distribution of light. These units are ideal for general floodlighting applications.
Asymmetrical floods incorporate an asymmetric reflector, producing an uneven distribution of light. This is of use when positioning the flood close to the top of a backcloth, avoiding an unattractive hot-spot at the top of the cloth.
A luminaire with a convex lens constructed with concentric steps, producing a soft-edged beam of light. The fresnel is suited for use above the stage where it can be used for general cover and colour washes. By moving the lamp and reflector assembly in relation to the fixed front lens, a wide variation in beam angle is produced. Additional control is provided via use of barndoors.
The PC luminaire is similar in character (and usually size) to the fresnel, but produces a light with less scatter outside of the main beam, giving a semi-hard edged quality. This is achieved by use of a convex lens with some diffusion built in to the back (inside) of the lens. Variation in beam angle is produced by moving the lamp and reflector assembly in relation to the lens: the variation is usually slightly wider than in a fresnel luminaire.
A variation on this type of luminaire is the plano-convex, which uses a different type of diffusion on the lens. However, this unit is not as commonplace as the prism-convex.
Profile luminaires are used wherever a defined light beam is required, without spill. The traditional 'spotlight' effect can be created by focusing the beam to a hard edge; alternatively the edge of the beam can be softened by moving the lens. There is usually a peak adjustment control, which slightly changes the position of the lamp in relation to the reflector. This allows the user to vary the style of the beam: from a brighter spot in the center, to one of uniform brightness across the beam diameter.
Profiles are equipped with four shutters, which can be pushed into the light path to create straight edges to the beam. Next to the shutters is an optic gate which accepts a gobo for projecting images or patterns, or an iris diaphragm for reducing the size of the light beam. Profiles are best suited for lighting the stage from the auditorium; projecting gobos or hard-edged specials; or as a cross-light from the wings.
Zoom profiles (also called 'variable beam' profiles) utilise two lenses to provide a wide range of beam angles (size of the spot) and edge variation (hard or soft focus). This is achieved through differential movement of the two lenses.
Profiles with Condenser Optics achieve a smooth flat field of light through use of an extra lens between the lamp and the optic gate. This makes them ideal for gobo projection and sharply focussed beams. The condenser optics promote more efficient use of the lamp's output.
Commonly referred to as 'Pars', this type of luminaire is lightweight and produces an intense beam of light. Common on live music events, particularly when combined with a smoke machine, they have migrated to stage use.
The tungsten-halogen lamp incorporates an internal parabolic aluminium reflector, together with diffusion built-in to the front surface. The type of diffusion (clear, ribbed, or stippled) produces a fixed beam angle (narrow, medium, or wide). Standard or short-nose versions are available in a variety of colours.
There are several types of parcan, identified by the size of the lamp:
Beamlights are similar to parcans, in that they produce a high intensity beam of light. The beam can be adjusted slightly by moving the lamp in relation to the reflector, but is always near-parallel. Beamlights are most commonly used as soft-edged followspots from the auditorium or onstage.
Projectors are used in the theatre to produce special visual effects. The effects projector allows realistic weather, water and fire to be created and controlled. Effect discs and their associated motor fit into a slot on the front of the projector head. The size of the projected image is related to the distance to the projection surface, and the focal length of the lens used.