In this section you will find several basic definitions that are essential in the understanding of the quality and the quantity of light produced by a lamp.
Light Flux (in Lumen or Lm):
A light flux is the quantity of light and is the first thing you should look
at when purchasing lamps. This quantity provides an objective point
of comparison between lamps, as it is independent from the technology
used. During the life of the lamp, the output light flux decreases until it fails.
Lamp Efficacy (in Lumen per Watt or Lm/W):
Lamp efficacy is the ability of the lamp to transform electrical energy into visible
light. Basically, the higher the efficiency, the more energy efficient the lamp
is. Lamp efficacy may vary depending on the employed technology, and usually
increases with the wattage of the lamp.
Luminance (in Candela per Square meter or cd/Sqm):
The luminance of an object is the most complicated notion in lighting.
It relates to how bright an object is - this includes light sources, surfaces
reflecting light and materials transmitting light.
Illuminance (in Lux or Lx):
The illuminance describes the amount of light that a specific surface receives,
and is the ratio between the amount of light reaching the surface, in Lm,
and its area in Sqm, so an illuminance of one lux is one square meter area
receiving one lumen of light.
The illuminance depends only on these two parameters, and is therefore
independent of the technology employed.
Colour Temperature (in Kelvin or K):
The colour temperature of a lamp is a quantification of the colour of light. A
low colour temperature is classed as warm, as the light has a yellowish
colour, whereas a high colour temperature is classed as cold, due to the
bluish shade of the light emitted. Most of the lamps are sold with
different colour temperatures such as “warm white” and “cool white”.