Looks like a great App! I used to do something similar, but I ran into issues with using an outdoor light sensor for indoor lighting, and I had the issue of defining what lux level is cloudy.
There really are not specific lux levels for that, as it all depends on time of day. That is why I wrote the SunCalc Illuminance Driver, that compares the lux from the sensor to a calculated expected lux for any minute of the day, to determine an actual lux % that stays consistent through the day.
I also used to use my outdoor light sensor for indoor lighting, but I found it is much better to just use indoor light sensors for indoor lighting. So I have another app for indoor lighting that only uses indoor light sensors, and it drives the room to a set lux level based on how much sunlight is coming into the room. When light changes in the room, my app acts as a governor to adjust levels until the lux level in the room matches the room lux setting. It creates very gradual transitions that are not noticeable.