A beam projector is a lenseless stage lighting instrument

Stage lighting instrument

Stage lighting instruments are used in stage lighting to illuminate theatrical productions, concerts, and other performances taking place in live performance venues. They are also used to light television studios and sound stages.Many stagecraft terms vary between the United States and the United...

 with very little beam spread. It uses two reflectors. The primary reflector is a parabolic reflector

Parabolic reflector

A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...

 and the secondary reflector is a spherical reflector. The parabolic reflector organizes the light into nearly parallel beams, and the spherical reflector is placed in front of the lamp to reflect light from the lamp back to the parabolic reflector, which reduces spill. The result is an intense shaft of light that cannot be easily controlled or modified. Beam projectors are often used to create a godspot

Godspot

A Godspot is an effect used in stage lighting for the theatre.The effect is created using a powerful spotlight placed directly above the stage at an angle of less than 10 degrees from vertical, i.e. almost straight down...

 effect. The beam projector no longer is used to the extent that it once was, as newer fixtures and PAR lamps

Parabolic aluminized reflector light

A parabolic aluminized reflector lamp is a type of electric lamp that is widely used in commercial, residential, and transportation illumination. Usage includes locomotive headlamps, aircraft landing lights, and residential and commercial recessed lights...

 have created easier ways to produce the effect. A similar effect can be produced using ETC Source Four PAR fixtures without a lens. A snoot/top hat can be added to control spill.