Here's one explaination that I found, but there doesn't seem to be much written about it, and it is definantly a factor in joint pain
Ultraviolet A and Ultraviolet B can actually damage DNA near the surface of the skin, altering the DNA and causing the formation of antibodies, thus, creating a lupus flare. Some individuals with lupus report rash, fatigue and aching upon exposure to the sun.
Thank you Karenboss-first answer I have gotten that explains the connection for me. Thank you too for the web site--never saw it until today, printed the entire thing. KarenLee