Parcans are luminaires which consist of a chassis and a PAR lamp, which is a relatively large parabolic reflector and a light source, sealed into one unit by a hardy Pyrex glass envelope. The elongated filament, reflected by the parabolic reflector, creates an elliptic beam, described by two angles of the long and short axis of the ellipse of light. A ring of 1000w very narrow spot (VNS) PAR-64s create an intense and directional ring of top light on the stage. The Turn Of the Screw, The New Israeli Opera.

The size of the beam depends on the diameter of the reflector, used in theatre in sizes 64, 56, 46 and 36 but also available in other sizes. However, the finish of the glass envelope affects the light distribution. Beam angles of PAR lamps are commonly categorized as: WFL (wide flood), MFL (medium flood), NSP (narrow spot) and VNSP (very narrow spot).

PARs have an extremely high luminous efficacy and are one of the least expensive luminaires available. The lamp is much more rugged than ordinary theatre lamps, and is much cheaper. These considerations make the PAR extremely popular for rock and roll concerts and other travelling shows. The most common PAR lamp in theatre is the PAR64, used in all beam angles, for various purposes. WFL or MFL PARs are used for strong, general washes. NSP and VNSP PARs are often used for intense and directional color washes, backlight or toplight.