I got a Metriful indoor air sensor, and wrote some code to expose it as JSON. It’s definitely not much:
Looking again at the website, I see that 8 days ago they added what is hopefully a much better version of what I started. Yay!
EDIT: Yep, it’s way better:
Here you can see the light levels as the sun set, followed by turning on a lamp in that room for about an hour.