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.
I just bought my first Vallhorn and connected it through ZHA and with rechargable batteries (1.2V). The sensor is located in the entryway away from a window. Sun is coming in over the day and it is dark at night.
As you can see i have a similar constant illumination reading as @Mathguy60 . Does anybody know already if this is a bug somewhere or that mine is faulty. Motion work 95% of the time ok (and the other 5% it does not detect motion).
I returned mine and the replacement Vallhorn reported the ligth value correctly. And bought another one, and that one reported movement constantly even when placed in a closet :-(. So it seems for this price you can’t expect all units to function 100% so you’d better buy one or two extra, and find out which one(s) to return when testing them at home.
Can you send me a screenshot of what is considered normal? So that I have a reference.
necro-ing this, but wanted to report that I had this problem with a new Vallhorn sensor I set up yesterday. All sorts of erratic light level values.
The solution was actually pretty simple. I removed the device from ZHA, then on the device I ran the reset function (4 taps of the sync button within 5 seconds), then I told ZHA to add devices. Once paired again, it picked up the same entity/device names it had before, so my automations and history and such continued. Here’s how the illumination sensor history looks for the before/after the reset:
Mine behave nice on ZHA, even if I have some weirdly laggy motion detection sometimes.
Beware scale is Log
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I tried replaced the batteries from 1.5V to Ladda 1.2V and I tried to reset the device but either not helped for me 
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It is resolved for me. I think the poor zigbee network was one of the reason. The homeassistant choosed the 11 channel, but this is used by the 2.4 GHz wifi and I think there was a lot of interference at home.
Be care full: if you change the channel, you have to reregister all of the zigbee devices!
After the vallhorn reregister, it is not worked for me. The lx was 0 all the time.
So I clicked the reconfigure button a few times while at the details window was everything green. And it is working now perfectly.
Before:
After:
