Lighting Terms

Absorption

Loss of light when light rays strike or traverses any medium. The ratio of light absorbed by a material to the light falling upon it is called the "absorptance" or "absorption factor".

Diffuse reflection

A beam of light is reflected diffusely, that is, its ray is scattered in all directions, if it stroked a rough or matte surface.

Specular reflection

A beam of light is specularly reflected when a light ray striking a shiny or glossy surface at an angle of incidence is reflected as the same beam with equal angle of relction.

Reflectance

Also called "reflection factor"; it is the ratio of light reflected by a surface to the light falling upon it.

Transmission

It is the passage of light through a medium when light falls upon a transparent material. It is "refracted" or bent as it passes through the material but emerges at the same angle that it entered.

Diffused transmission

When light passes through a translucent material (such as plastic) and the emerging rays are spread in all directions, it is called "diffused transmission."

Transmittance

Also called "transmission factor"; it is the ratio of light transmitted to light striking the surface.

Accent lighting

Directional lighting to emphasize a space or an object.

Downlight

A fixture producing concentrated direct lighting from a single bulb.

High hat

A term often applied to a can-type of recessed incandescent downlight

Eye ball

Recessed or semi-recessed lighting unit with a rotating spherical element that may be turned to project light to any direction.

Lumiline

A tubular fluorescent lamp with a disc base at each end.

Luminance ceiling

A false ceiling of diffusing material with light sources mounted above

Filter

Device which changes either amount or color, or both, of light passing through it.

Dimmer

A device to control the amount of light by reducing the voltage or the current; also called a "rayostat".

Capacitor

An electric component which consists of conducting plates insulated from each other by a layer of dielectric material; introduces capacitance into a circuit.

Capacitance

The quantitative measure of electric-energy storage capability of a capacitor; usually measured in farads or microfarads.