In order to select the most appropriate luminaire for a specific purpose we need to be able to compare the technical specifications of the various luminaires at hand. These specifications can supply us with information such as the intensity, beam and field angle, and focus angles which the luminaire can achieve.

Manuals and catalogs of theatrical luminaires usually contain the following data:

Type of luminaire Floodlight, PAR, PC, fresnel, profile-spot and so on.		Light source The type of lamp (incandescent or discharge), base type and so on, the rated   voltage, rated wattage and rated life (in hours) for lamps.		Lens characteristics The type and number of lenses and lens information such as diameter and focal length.

Intensity and light distribution The light distribution pattern of the luminaire, beam angle, field angle and cut-off angle, efficiency and light output (Lux, fc), and the intensity of the luminaire at various  distances.		Structure and special characteristics Mounting methods, focus methods, shutter systems, special lenses, special reflectors, and additional mechanized features such as rotating shutters, forced ventilation and so on.

Dimensions and weight The length, width, height and weight of the luminaire		Accessories Barndoors, shutters, gobo holders, irises, color frames, color changers and so on.		Safety features Safety chains, devices such as microswitches which prevent access to a live lamp,  low chassis heat, safety wire mesh and so on.

It is important to note that the data available for different makes of luminaires may be differently presented which may make comparison difficult. One must keep in mind that every manufacturer wishes to present its product to its best advantage in the technical specifications. When a luminaire is used on the stage and time goes by, other factors must be kept in mind, all of which will affect the light output of the luminaire, such as reflector deterioration, lamp age, dust accumulation, poorly aligned optical systems and so on. Thus a luminaire which has not been well maintained will compare unfavorably with its original technical specifications..