Brightness

The brightness of light sources

 

Brightness is part of the light quality

The brightness of illuminants describes one of the central quality features of light. But how to draw a conclusion on the actual brightness of a lamp based on the specification on its packaging.

In the past, it used to be so easy: the most common light sources were conventional incandescent lamps. Their brightness could be determined by simply looking at the wattage specified. Due to the gradual phase-out of inefficient illuminants, incandescent lamps were removed from the market step by step. There is a number of alternatives that are suitable to replace the incandescent lamp. However, here it is not the wattage that determines the brightness but the unit "lumen" (lm). But how to compare different light sources? How many lumens correspond to 60 watts?

Strictly speaking, there is no answer to this question since these are different units of measurement that are set in relation to each other. While the lumen specification specifically describes the luminous flux, the wattage only makes a statement on the electrical power of an illuminant. It is only out of habit that we have a concrete idea of brightness based on a specification like "60 watts".

 

Lumens per watt

A more meaningful comparison is possible on the basis of the specification "lumens per watt", which describes the efficiency of an illuminant. An example: a conventional incandescent lamp with a power of 60 watts achieves a light output of approx. 710 lumens. This corresponds to about 12 lumens per watt. Compared to this, an energy-saving lamp with a power of 12 watts, which achieves an equivalent light output as a 60 W incandescent lamp, has a luminous efficacy that is five times higher (60 lumens/watt).

In order to make the selection of a suitable illuminant somewhat easier, we always indicate a lamp with a comparable brightness as a reference. This way, everyone is able to quickly get an idea of the actual brightness of a light source. The brightness of the selected illuminant is indicated by specifying the exact lumen output on the corresponding product page.