This looks like the API I was looking for to compute the best screen brightness in the absence of a light sensor in Lunar [0] I would probably do a request per day for each user of this feature, which would amount to about 300-400 requests/day. Would that fit in the non-commercial use tier? I would be happy to start paying like $5/month if I'll find a way to improve the brightness calculation logic with your API. If…
Regular "shortwave_radiation" should fit your needs. This is basically "direct_radiation + diffuse_radiation".
I am not entirely sure, if this effects your users that much, because many will work indoors and only a fraction of sunlight will get in.
You can contact me directly via mail for a non-commercial use waver.