I don't see any ZigBee illumination sensor in the list of supported devices. I'm looking for a recommendation.
I'd like to change evening lights to trigger using a light level sensor instead of sundown time. That way they will adapt cloudy skies, etc.
Also, can someone confirm if an illumination sensor is the same thing as a flux sensor?
Thank you
The Hue motion sensors--both the indoor or outdoor models--measure illuminance besides just motion (and temperature). It might be overkill for just illuminance, but it would certainly work, and there's no reason you have to use any other feature just because it's there. The homemade "environment sensor" device a community member made can also measure lux, but it's meant to be USB-powered and so might be more difficult to place. I also know some community members have experimented with the Xiaomi Mijija Light Sensor (model GZCGQ01LM), but it's not officially supported. Some Xiaomi devices have been problematic for some Zigbee meshes in the past, and I'm also not sure if this device continues that trend or not. I would avoid the Xiaomi motion sensor (a few of which also do illuminance) for both this reason and the fact that I don't think any report illuminance without motion.
If you're not opposed to Z-Wave, there are a few more options in that arena, though mostly also motion sensors.
If you mean "lux," then yes. (That is a common unit of measurement for this value and is also the Hubitat standard for it.) Not sure what flux would do, though. 
+1 for the Hue outdoor motion sensor....zigbee, pairs directly to hubitat, uses standard AA batteries, and highly recommended by most of us that have them.
I have 4 of these and they work great, and I paid $10 each (on aliexpress). They've so far gone 16 months on the original CR2450 battery.
BUT
To make Aqara/Mijia devices work reliably, you need to have certain Zigbee repeaters on your network, otherwise these devices will fall off the mesh. I use Ikea Tradfri Zigbee plugs, and they make these devices rock solid. This is described in many threads in the community.
(the "problematic for some Zigbee meshes" just means the device will fall off the mesh; it doesn't cause issues with other Zigbee devices on your mesh)
Thanks for your advice everyone, and especially bertabcd1234 for your extra complete answer.
I found the outdoor Hue sensor on bestbuy.ca, but not the indoor one yet.
I would have tempted by the one on AliExpress, but with all the shipping delays it'll probably take months to get here.
These work well…
Xiaomi Mijia Smart Light Sensor Zigbee 3.0 Light Detection Intelligent Linkage Waterproof Used With Smart Multi-mode Gateway
This is the same one I talked about 2 posts above. Your aliexpress link is the one I bought from, but it now shows out-of-stock, and I can't successfully find them on aliexpress anymore. In the US, they are available at walmart.com for between $15 and $18 (search GZCGQ01LM), shipped from China.
I have one of these (also from Ali Express) and it has been rock solid on my hub, and no special Zigbee repeaters required. I've had it for over a year and battery still shows 100...
Did you actually use the plugs? Or did you use the Tradfi signat repeater? Do the plugs act as repeaters? if so, seems odd that the dedicated repeaters cost more than the plugs.
I have the Tradfri plugs; they do act as repeaters. As you note, they were cheaper than the dedicated repeaters.
I don't actually control anything with the plugs; they only exist in my house as Zigbee repeaters, and only so that Aqara/Mijia devices don't fall off the mesh. I do wish at this point I'd bought at least 2 repeaters instead of plugs, simply to let them be a USB outlet in the guest bedrooms.
Thanks for clarifying. Sounds like I need to do a run down to IKEA. I’m having a bear of a time keeping my Sonoff contact sensors and motion sensors from dropping off constantly. Maybe that’s plugs will help with Sonoff devices as well. 
FWIW, I've only heard of this problem with the Aqara and Mijia devices, which use something non-standard in their Zigbee protocol implementation. I've never heard of that problem with Sonoff sensors (although I don't have anymore, so I don't pay attention).
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