Reference number (headlights)
The reference number is a designation for main-beam headlamps. It relates to the maximum luminous intensity of the high beam and serves, amongst other things, to assess the permissible combination of several high beam lights on a vehicle.
The reference number is indicated on the light itself or in the vicinity of the ECE test mark.
Meaning of the reference number
As a general rule: the higher the reference number of a main-beam headlamp, the higher its maximum luminous intensity. This index must not be confused with the luminous flux in lumens. The luminous flux describes the total amount of visible light emitted. The luminous intensity relevant to the reference index, on the other hand, describes how strongly light is emitted in a specific direction. A highly focused high beam headlight can therefore achieve a higher maximum luminous intensity than a wider light distribution, despite having a comparable luminous flux.
On high beam headlamps, for example, reference figures such as 7.5, 10, 12.5, 17.5, 20, 25, 27.5, 30 or 37.5 can be found. The reference figure has no unit.
Multiple high-beam headlights
If several high-beam headlights are used simultaneously, the permissible total luminous intensity must be observed. To do this, the reference values of the main-beam headlamps switched on simultaneously are added together. According to UN Regulation No. 48, the sum of the reference values of the main-beam headlamps that can be switched on simultaneously must not exceed 100. This corresponds to a maximum total luminous intensity of 430,000 candelas.
Example: If a vehicle is fitted with two high-beam lights with a reference value of 25, which are operated simultaneously, this results in a total of 50.
The reference value thus allows for a simple check of the permissible combination without having to calculate the luminous intensities of the individual lights separately.
Legal classification
The requirements for the photometric characteristics of high-beam headlamps are laid down in particular in UN Regulation No. 149. The regulations governing the fitting and combination of high-beam headlamps on vehicles are set out in particular in UN Regulation No. 48.
Further markings and their meanings are explained in the article indications on lights.