How do you approach your boss?

Sounds like you have covered the basics - I've found telling the truth about an illness, even if we think it makes us look weak or needy, is usually met with compassion.

You might check on the costs of the fluorescent light covers - I know other teachers have found them quite expensive and have offered to bring in some incandescent lamps.

I'd tell him the lights are affecting your health, you didn't expect it, here are the options I've found, what you're willing to do, and what does he think. I would just say photo-sensitivity unless he asks for details - maybe tell him how you plan to take care of yourself outside.

It does more than the symptoms you mentioned -- it adds to overall stress, which always makes lupus symptoms a big more troublesome. Good luck!