Lighting Glossary

Lighting has it own technology and terms to define the characteristics of the lamps and luminaires and for standardising he units of measurements.

Luminous flux
Unit of measurement: lumen [lm]
All the radiated power emited by a light source and perceived by the eye is called luminous flux.

Luminous Intensity
Unit of measurement: candela [cd]
Generally speaking, a light source emits its luminous flux in differencet directions and at different intensites. The visible radiant intensity in a particular direction is called luminous intensity.

Illuminance E
Unit of measurement: lux [lx]
Illuminance E is the ratio between the luminous flux and the are being illuminated.

Luminance L
Unit of measurement: candelas per square metre [cd/m2]
The luminance L of a light source or an illuminated area is a measure of the brightness.

Colour temperature
Unit of measurement: Kelvin [K]
The colour temperature of a light source is defined in comparison with a "black body radiator" and plotted on what is know a the "Planckian curve". The higher the temperature if this "black body radiator" the greater the blue component. An incandescent lamp with a warm white light, for example, has a colour temperature of 2700 K, whereas a daylight fluorescent lamp has a colour temperature of 6000 K.

Sources from Osram.