valokeila

Valokeila (Finnish for "beam of light") is a directional stream of electromagnetic radiation, usually visible light, but it can refer to any wavelength. It is produced by a light source that concentrates light into a narrow pathway, such as lasers, projectors, headlights, or optical fibers.

In optics, a beam is characterized by its divergence (beam angle), cross-sectional diameter, intensity distribution, wavelength, coherence and polarization. A collimated beam has small divergence, approaching parallel rays, as in laser beams. A non-collimated beam spreads with distance. The term is contrasted with diffuse illumination where light is emitted in many directions.

Beams can be natural, e.g., sunlight passing through a small aperture or reflecting from a surface into a narrow path, or artificial, produced by devices. In everyday technology, valokeiloja includes LED flashlight beams, stage spotlights, and traffic-lane illumination.

Applications of valokeila concept include measurement and instrumentation (optical alignment, laser rangefinding), manufacturing (laser cutting and welding), communication (fiber optic transmitters emit beams), cinema and stage lighting (spotlights), and scientific research (optics experiments).

Safety: laser beams can pose eye and skin hazards; beam management, shielding, and eye protection are important for high-power beams.

History and etymology: the term combines valo "light" and keila "beam" or "cone," reflecting its directional nature.