Intensity of illumination (lux, lx)
A unit of measurement that indicates the amount of luminous flux per unit of surface area.

Economic service life
The time it takes until a given proportion (often 70% or 80%) of the installed luminous flux remains in a facility, taking into account both bulb loss and decreased light output.

Energy efficiency (lumen/Watt, lm/W)
The efficiency of a light source. See “luminous efficiency”.

Color temperature (Kelvin, K)
A measure of the color of the light from a light source. Defined as the temperature at which the “black body” (see below) has the same color characteristics as the light source.

Color rendering
A measure of how well a light source renders colors. Color rendering is expressed by an Ra index on a scale of 1 to 100, with 100 being the best value.

Luminous flux (lumen, lm)
Indicates how much light a light source is emitting.

Luminous intensity (candela, cd)
Indicates the amount of luminous flux traveling in one direction from a light source.

Luminous efficiency (lumen/Watt, lm/W)
The ratio of the luminous flux to the power supplied to a light source.

Luminance (candela/m2, cd/m2)
Light density. Indicates how bright a surface looks.

Average service life
The time after which 50% of the bulbs are still functional.

Black body
A theoretical energy radiator defined as a body that emits a maximum of radiant energy at all temperatures.