Technical lighting terms

Correlated Color Temperature (CCT)

This refers to the apparent color of the light source. 2800K – 3200K is considered “warm” 4100K-4900K is considered “white” and 5000K or above, “cool.” This term comes from heating a blackbody (think of a piece of coal) up to a certain temperature; as the coal gets hotter and hotter, it changes from orange (i.e., 2300 K) to yellow (3000 K) to white (4700 K) to blue (5000 K).

Color Rendering Index (CRI)

The measure of how well a light source replicates a given lighting condition; 100 being perfect and consistent with natural daylight, 90 fair and 80 poor.


A measurement of light quantity as is perceived by the human eye, i.e., the brightness of a light source.

Foot-candles / Lux 

Measurement of illuminance or light output. Both foot-candles and lux measure the same thing, but foot-candles are measured using the imperial sytem and lux is measured using the metric system. Lux = 1 lumen per square meter. Foot-candle = candela per square foot. 10 lux or 100 foot-candles (100 fc) is generally considered enough light to perform most tasks. 

Beam Spread

Refers to the divergence angle of the light exiting the lamp. The smaller the degree of angle, the tighter and brighter the beam. Flood light, spot light, etc., are all references to the beam spread of a lamp.  

Candle Power

Used by lighting designers to calculate the foot-candles illuminating a surface (C.P. /distance in feet squared) or Lux illuminating a surface (C.P./distance in meters squared).


Combination of direct sunlight and skylight. Best light for optimal color rendering.

Infrared Radiation (I.R)

Associated with sunburns and heat. Infrared radiation refers to the lower energy, long wavelength energy situated at the red end of the visible light spectrum.

Ultraviolet Radiation (U.V.)

Associated with suntans and fading of pigments and dyes. High-energy short wavelengths before the blue end of the visible light spectrum.


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