Watt
Watt (W) is the SI unit of power. For electrical appliances, the wattage indicates how much electrical energy is consumed per unit of time.
In the case of a light fitting or a light, the electrical power indicates how much power the device draws whilst in operation. However, it does not directly describe how much light is produced.
Watts and luminous flux
With modern light sources, there is no fixed relationship between electrical power consumption and the luminous flux emitted. Two lights with the same power consumption can therefore produce different luminous fluxes. Conversely, two lights can achieve a comparable luminous flux even though their power consumption differs. Key factors include the efficiency of the light source used, the electronics and losses within the light.
Luminous flux is measured in lumens. Watts and lumens therefore describe different properties and cannot be equated with one another.
Watts say nothing about the beam pattern
Nor can the illumination of a work area be assessed on the basis of wattage. In addition to luminous flux, the way the light is distributed by reflectors, lenses or other optical components is crucial. The resulting beam pattern largely determines where the emitted light is actually available. The illuminance falling on a surface, on the other hand, is specified in lux.
A high power consumption therefore does not automatically mean a high luminous flux or better illumination.
Significance in vehicles
In the case of vehicle lights, however, power consumption is still an important technical parameter. Among other things, it determines the load on the vehicle’s electrical system and is relevant, for example, to the design of wiring, fuses and electrical components.
When selecting a light, therefore, both the electrical power consumption and the photometric properties relevant to the specific application should be taken into account.