Indoor artificial light typically measures around 1000 lux, whereas outdoor sunlight can range from 5,000 to 90,000 lux, with this diffuse, bright sunlight being crucial for setting brain and body rhythms.

“Wake up in the morning, take Light Meter, point it at the brightest light in your home, and take a measurement, and what you'll probably find is it's about a thousand lux. Now go outside and if there's some sunlight out and there's cloud cover, point it at the sky and press that button. You can actually hold it down and it'll give you a dynamically updated lux measurement. And what you'll find is like 5,000, 10,000, sometimes even 90,000 lux, even though you don't experience it as so much brighter, and that's because an indoor artificial light is very concentrated over a small spatial area whereas the sunlight is very diffuse. But it's that diffuse, very bright sunlight, that photon energy, that you really want that's going to set all the rhythms of your brain and body in the proper way.”