How do window tint medical exemptions work?

A medical exemption lets a driver or regular passenger with a certified light-sensitivity condition, such as lupus, porphyria, or albinism, run darker tint than the state's normal limit. A licensed physician (in some states an optometrist, physician assistant, or nurse practitioner) certifies the condition; some states issue a certificate or permit, others accept the signed statement. Limits often remain: Georgia stops at 23% on front side windows with no windshield tint, and California's and Pennsylvania's exemptions don't cover dark film on front side windows. Georgia's exemption lasts 4 years and North Carolina's permit 5. Shops should keep a copy per vehicle and record the installed VLT.