Just as Lupus (and other auto-immune disorders) affects each one of us differently, so is our tolerance to the sun different for each of us. Some of us can manage and hour or two, while others can only handle a few minutes (As Sits-In-The-Corner indicated).
With reference to sunscreens; SPF numbers on sunscreens only cover UVB, the type of rays most responsible for burns. UVA is far less responsible for burning, but still can raise skin cancer risks and can still cause problems for those of us with Lupus. Only one sunscreen in five has effective UVA protection. There are ingredients that protect well against UVA, but sunlight can break down and make them ineffective if they are not formulated well. Try to find a sunscreen that contains avobenzone, titanium dioxide, zinc oxide (or Mexoryl SX), or Helioplex).
Since sunscreens are always an issue this time of year, I've placed a post in "Lauri's Lounge" with sunscreen information for everyone to read.
Peace and Blessings
Look For The Good and Praise It!