Automatic switch-on

The savings potential of presence detection (see also chapter „German standard DIN V 18599”) on the one hand depends on the degree of absence detection. Another factor, however, is the function of switching back on. It can be triggered automatically when detecting presence again, or manual switching on can be required. For the purpose of energetic lighting optimisation, these two factors should be considered in combination to a certain extent.

In many applications, the degree of absence detection essentially depends on the hold time which needs to pass after the last motion is detected before the light is switched off.

For instance, if the hold time is set to 15 minutes in a corridor that is frequented on average half-hourly, the maximum savings potential that can be expected is 50%. When reducing hold time to one minute, however, ca. 95% of energy required for permanent operation can be saved. The prerequisite is that the detection of presence by suitable sensors and an optimised arrangement is good enough to not skip for one minute. For safety reasons, automatic switch-on should be activated here for cases of newly detected movement. This is also referred to as a "fully automatic switching function".

Another example would be a school classroom. Since there is little to no movement over periods of time, a very short hold time would lead to frequent switching off of the lighting. Besides the disruptive impact, it would be necessary to activate automatic switch-on to avoid having to perpetually switch the light back on manually. If the hold time is extended in a way that allows for presence detection to function reliably within its time span, automatic switching on is not necessary for the lighting. In combination with daylight utilisation, this means great savings potential since the light needs to be switched on deliberately (see section 2.4.3). Hold time here should be 5 to 10 minutes so that the lighting is switched off during classroom breaks. This is also referred to as a "semi-automatic switching function".

Consequently, the required hold time depends on sensor capacity and arrangement to bridge periods where presence is not detected reliably. On the other hand, it should be short enough not to waste the possible potential for energy savings.