Lighting Terminology Glossary

Beam angle measures the distribution of light from a bulb or fixture. It can be represented by one or two numbers depending on the distribution type.

Correlated Color Temperature (CCT) is a method of displaying the relative 'color' of white light from artificial sources in a range from warm (lower numbers, e.g. 2700K) to cool (high numbers, e.g. 6500K).

Color rendering index (CRI) measures the quality of artificial light compared to natural sunlight, with higher numbers (e.g. 90+) representing higher quality light.

Foot-candles show the available light per surface area at a specific distance from a light source. As a unit, one foot-candle is equal to one lumen per square foot.

Glare is a form of light pollution caused by an excess of light being projected into the eye. The intensity, beam angle/distribution pattern, view angle, and overall design of the light can all affect this.

High-intensity discharge (HID) lights produce light by creating an arc between tungsten electrodes. This type of light requires a ballast to operate unlike standard incandescents or LEDs.

Generally, high bay refers to lighting meant for commercial and industrial spaces that is mounted 20 ft or more off the ground.

Hot spots in LED lighting refer to differences in intensity, usually related to low density of LEDs and/or lack of diffusion of a light source. This difference manifests as noticeably bright dots where the LED chips are placed, rather than a smooth, even light output.

Incandescent light technology is one of the oldest and most common types of lighting. These bulbs heat a metal filament so that it glows, creating light.

LEDs (light-emitting diodes) are semiconductor diodes that emit light when current is passed through them.

Lumens measure the peak total calculated output—sometimes called intensity or brightness—of a light.

Lux shows the available light per surface area at a specific distance from a light source. As a unit, one lux is equal to one lumen per square meter.

Spread measures the distribution of light from a bulb or fixture. It can be represented by one or two numbers depending on the distribution type.

'UFO' is a term applied to round high bay lights commonly found in commercial and industrial locations due to their shape.