I’ve installed an Ikea Vallhorn motion sensor. Motion detection is OK, but de readings of the light sensor fluctuates from 9 to over 500 all the time (including the night). Looks like the high values are wrong. If I connect all the low values, I kind of get a decent graph of the light. Anyone experience the same thing? Or even better: anyone have a solution?
I have a Vallhorn motion sensor in a location that is normally completely dark. The light level increases only when a door is opened (the detected motion serves to turn on an overhead light). The device’s firmware is version 1.0.64 and is integrated via Zigbee2MQTT.
As you can see from the following graph, the reported illuminance is normally 1 lux and increases only when the door is opened.
I don’t know whether it is related to this particular sensor as well. But I have heard from several people that the Vallhorn PIR produces quite some false-positives when powered with regular alkaline (1.5v) batteries. They issues disappeared when the PIR was powered using rechargeble batteries (1.2v).
So you might want to try replacing the batteries for (for example) Ikea Ladda batteries. If it doesn’t help for the illuminance, it might help against the false-positives. 
I have Ikea Ladda batteries in the sensor (and no false positives). It’s just the light values that behaves strange.