Hubitat has a native driver for Open Weather Maps (OWM). You need to get a free API key from their website: Pricing - OpenWeatherMap
If you want more features that what is available with the native OWM device, you can install this device driver: see below
Once the device is in your device list, just load in your location and API key and you will have a device with a lot of weather attributes. Changes to any of these attributes can trigger a rule to run. In your example you would use the attribute "Lux". I am not sure but you may need to use the custom driver posted below (as opposed to the native driver) to get a lux value.
Sorry @kosmicken I think I gave you the wrong link to the custom driver, this is the link: OpenWeatherMap-Alerts-Weather-Driver
