Photophobia

Photophobia: Painful oversensitivity to light. For example, there is photophobia in measles (rubeola). Keeping the lights dim or the room darkened may be useful. Sunglasses may also help.

Whereas most phobias are abnormal, excessive, and irrational, Photophobia is usually an appropriate rational response. It is also rationally derived from the Greek "phos" (light) + "phobos" (fear).