Definitions of Lighting Terms

Accent Light - Illumination used to make something stand out. It may be done with intensity and/or color. A luminaire that provides such illumination.

Average Illuminance - a specified surface area the mathematical mean of the illuminance values, calculated or measured, from within the area.

Beam Angle - The angle of the vertex of a cone shaped beam where the perimeter of the base is defined by where the intensity is 50% of the maximum intensity.

CA-90 Luminaire - A recessed luminaire that can be used where normally flammable materials, including building insulation, but cannot be covered in normal use. Building elements, building insulation or debris have limited access to the heated parts of the luminaire.

Colour Temperature - The temperature, in degrees Kelvin, a measure of the colour appearance of the light source.

Cool Light - Light source having a colour temperature of approximately 4000°K, bright-white, normally seen in commercial buildings.

CRI - Color Rendering Index: the ability of a light source to accurately reveal the colours of the object it illuminates, in contrast to a natural light source.

Cut-off Angle - The angle, in a given vertical half-plane, between the downward vertical axis and the line of sight at which all surfaces of high luminance just cease to be visible.

Diffuser - Made of diffusion material. Used for diffusing a light source being a luminaire or sunlight. Has the effect of reducing glare, and, in most cases, widening the beam angle.

Do-not-cover Luminaire - A recessed luminaire that can be used where normally flammable materials, including building insulation, are or may be present, but cannot be abutted against any material and cannot be covered in normal use.

Heat Sink - A luminaire component that is used to dissipate heat effectively. Heat sinks normally use materials with a high thermal conductivity and have a fin-like geometry so that their surface area in contact with the air is maximised.

IC Luminaire - A recessed luminaire that can be abutted against normally flammable materials, including building insulation, and can be covered in normal use. Building elements, building insulation or debris have limited access.

IC-4 Luminaire - A recessed luminaire that can be abutted against normally flammable materials, including building insulation, and can be covered in normal use. This classification is effectively a sealed unit that has restricted flow of air between the habitable room and where the luminaire is located.

ISTMT - In-situ Temperature Measurement Tests.

Initial Illuminance - The value of average illuminance which is initially provided by the lighting system, with a new clean light source, clean room surfaces.

LED - Light Emitting Diode. An LED is a solid state semiconductor device that emits light when conducting an electrical current. The birth of the LED goes back to the early years of the 20th century, when electroluminescence was discovered by British scientist H. J. Round. The modern principles of commercial LED technology was researched by Japanese scientists Isamu Akasaki, Hiroshi Amano and Shuji Nakamura in the early 1990s. Because LEDs can be embedded or built-in to just about any product surface, they have led to a range of new shapes, forms, and profiles in lighting design.

Light Level - The average illumination on a subject, normally measured in lux.

Light Pollution - Any lighting output emitted in unwanted directions, which may have negative consequences. An example of light pollution is when parking lot fixtures emit bright light sideways, exposing drivers to glare.

Lighting Designer - One who plans lighting compositions, lays out light plots, directs the focusing of luminaires, and determines the various intensities, colors, looks, and cues for a lighting production.

Lux - A metric unit of measurement for Illumination, i.e. 1 lumen per square metre.

Maintained illuminance - The defined level below which the average illuminance on any surface is not allowed to fall. It is the minimum illuminance at which maintenance operations, such as cleaning of fittings is to be carried out.

Non-IC Luminaire - A recessed luminaire that cannot be abutted against or covered by normally flammable materials or used in installations where building insulation or debris is, or may be, present in normal use. (not suitable for residential installations).

Safety Lighting - a form of lighting, energised from an alternative power source, which is intended to ensure that operating personnel can move to a place of safety, or control or shut down the process in a safe manner, in the event of failure of the electrical supply to the normal lighting.

Standby Lighting - A form of lighting, energised from an alternative power source, which in the event of failure of the electrical supply to the normal lighting, is intended to facilitate the continued performance of particular tasks or processes.

Task Area - The area within which the task is located. This may be the whole of the room or a small part of it.

Task Illuminance - The value of maintained illuminance which is recommended for a specific visual task.

Uniformity of Illuminance - The ratio of the minimum illuminance to the average illuminance on a given plane within the calculation or measurement area.

Wall Washing - Lighting effect where a wall is illuminated so that surface irregularities are minimised, so that it seems smoother.

Warm White - White light that is characterised by a yellow tinge. The term is generally used for lighting with a correlated colour temperature (CCT) of around 3000K. A common choice for residential spaces.

Working Plane - The plane horizontal, vertical, or inclined in which the visual task lies.