Light beam

A light beam or beam of light is a directional projection of light energy radiating from a light source. Sunlight forms a light beam (a sunbeam) when filtered through media such as clouds, foliage, or windows. To artificially produce a light beam, a lamp and a parabolic reflector is used in many lighting devices such as spotlights, car headlights, PAR Cans, and LED housings. Light from certain types of laser has the smallest possible beam divergence.

Visible light beams
A natural lightbeam in the Majlis al-Jinn (literally 'Meeting place of the jinn') cave in Oman

From the side, a beam of light is only visible if part of the light is scattered by objects: tiny particles like dust, water droplets (mist, fog, rain), hail, snow, or smoke, or larger objects such as birds. If there are many objects in the light path, then it appears as a continuous beam, but if there are only a few objects, then the light is visible as a few individual bright points. In any case, this scattering of light from a beam, and the resultant visibility of a light beam from the side, is known as the Tyndall effect.
Visibility from the side as side effect

Flashlight (UK 'Torch'), beam directed by hand
Headlight, forward beam; the lamp is mounted in a vehicle, or on the forehead of a person, e.g. built into a helmet
Lighthouse, beam sweeping around horizontally
Searchlight, beam directed at something

Visibility from the side as purpose

For the purpose of visibility of light beams from the side, sometimes a haze machine or fog machine is used. The difference between the two is that the fog itself is also a visual effect.
Laser beams used for visual effects during a musical performance
Laser beams with different wavelengths (405nm - 660nm).

Laser lighting display- Laser beams are often used for visual effects, often in combination with music.
Searchlights are often used in advertising, for instance by automobile dealers; the beam of light is visible over a large area, and (at least in theory) interested persons can find the dealer or store by following the beam to its source. This also used to be done for movie premieres; the waving searchlight beams are still to be seen as a design element in the logo of the 20th Century Fox movie studio.

Other applications

Optical communication
Infrared Data Association (IrDA) standards
Infrared remote control
Security alarms
Fibre optics
Laser pointer
Laser sight
List of applications for lasers