Besides presence/absence detection, electronic daylight detection also provides great potential for energy savings. The amount of daylight available does not need to be provided additionally by artificial lighting. Hence, the artificial light can be reduced by the respective amount and, in case of sufficient daylight, be switched off.
As early as the 1980s, this principle was used to save lighting energy, predominantly in large industrial or sports lighting installations. In many cases, this was achieved by means of a threshold switch which would switch off/on the artificial lighting in three switching groups once certain pre-set measurement threshold values of available daylight were reached. Current technology facilitates continuous dimming of the lighting so that exact upholding of required, pre-set lighting levels opens up additional potential for energy savings.
Thanks to modern technology, the additional investment for daylight-dependent, dimmed lighting installations is ecologically sensible and economically profitable in many cases – and at least justifiable in other cases. However, the energy savings potential should always be evaluated:
First of all, good lighting quality coupled with minimised connected load should be realised by using efficient luminaires.
The next step is to evaluate whether or not presence detection is expedient. If the application in question does not require a residual light level in cases of absence, it is usually acceptable to use non-dimmable luminaires.
The last step is to evaluate whether or not dimming of the installation in the operating periods which remain after subtracting absence-based switching-off periods offers an attractive energy savings potential for daylight-dependent dimming (see figure).
On this basis it is possible to make a decision about the details of the desired functionalities.