UV can come from indoor lighting, windows (even in the car), and screens. I use a filter on my screens, have replaced lights with leds, and put a uv film on the windows.
I am very sensitive to the sun, so it depends on how much it bothers you. I have UPF clothing that blocks the sun and use that in addition to sunblock if I have to go outside.

I get the same thing from the sun. In addition to sunblock, try getting SPF clothing! Coolibar, Lands End, North Face and other brands make clothing with SPF in it. Just be sure to not put these clothes in the dryer. I also wear these clothes when I drive and keep a long-sleeve SPF shirt in my car.

I wear spf everyday. Sunscreen is part of my daily face cream routine. I like revision skincare line. I have sensitive skin and it works well. EltaMD also has a good one. I also use neutrogena sunscreen spray for my body (doesnt have the sunscreen smell). It keeps the flares away and also protects against wrinkles! Win win

I have learned that with lupus - it's forever changing. Knowing this, I pay close attention to my reactions and try to really think about what I did prior to the reaction. I wear SPF, a hat and sunglasses when I go out now. I hate it b/c eww who wants to always have on a hat? This is when we will be out during the day. When I don't want to wear a hat our outings are planned in the evening when the sun is going down. So, I get maybe an hour of sunlight - I too suggest the SPF clothing but in general - you just never know what will trigger the lupus when it comes to light sensitivity. In my home - all of the lights are sensor dim switches. So when I walk in any room, the light comes on low - and after so many minutes it automatically shuts off. This keeps me from sitting under lights all day - as for windows I open the blinds b/c I LOVE natural light and get depressed in the dark. Lupus + darkness = sadness ... I don't sit in front of my windows and I adjust the blinds so the rays aren't aimed at me. I hope this helps!

I've been dealing with this for 38 years and it's still hard to know what causes things. Like somedays- something I was ok with one day causes a rash the next day. I have to be really careful with products I use. Even sometimes fragrances in stores can trigger it. It was really bad in the beginning of covid because there is usually fragrance added to hand sanitizer and that caused some issues. Good luck!