Impact of Sex and Age on Non-visual Light Input That Affects Sleep and Circadian Rhythms

Inclusion Criteria: * (i) 18-85 years old. * (ii) Habitual sleep onset 10 pm- 1 am (healthy controls only); * (iii) Habitual wake onset 5:30 am- 8:30 am (healthy controls only); * (iv) vision correctable to 20/30; * (v) stable medically. * (vi) ability to speak, understand, and read English at a high school level Exclusion Criteria: * (i) Color blind by Ishihara Color Blindness Test; * (ii) any history of eye trauma, surgery or abnormality (e.g., retinopathy, glaucoma, cataracts, amblyopia, macular degeneration, congenital color vision deficiencies, or any type of blindness) besides correctable vision abnormalities (e.g., with glasses); any abnormalities on clinical eye exam (e.g., neuritis, Neuromyelitis optica, treated or untreated glaucoma) such that the ophthalmologist recommends the participant not be studied; Limited cataracts (e.g., Lens Opacities Classification (LOCS) III grade \<2) will be allowed and documented during the eye exam. Eye drops that affect pupil size or contractility (e.g. mydriatics, miotics); drops to treat glaucoma (e.g., pilocarpine, brimonidine, other drops like artificial tear drops, or anti-inflammatory drops would not be exclusionary) * (iii) current or history of neurologic or psychiatric disease including autonomic function disorder or migraines; psychiatric disorder requiring medications in a first degree relative (healthy controls only); limited-duration counseling without prescription medications will not be exclusionary; (iv) current or history of circadian rhythm sleep-wake disorder (healthy controls only); * (v) prescription or non-prescription drugs affecting the pupil (e.g., affecting autonomic function), sleep, melatonin (e.g., lithium, alpha- and beta-adrenergic antagonists), and/or circadian rhythms (e.g., beta blockers, non-steroidal anti-inflammatory drugs, tricyclics); * (vi) Other disorders that can affect or may be affected by intrinsically photosensitive Retinal Ganglion Cell (ipRGC) function, including diabetes mellitus, multiple sclerosis, Parkinson's disease, seasonal affective disorder; * (vii) shift- or night-work in past three months; history of night work in preceding 3 year period * (viii) crossing more than 2 time zones in past three months; * (ix) presence of depression as assessed by a Beck Depression Inventory (BDI) score \>14. * (x) pregnant or less than 6 weeks post-partum or breast-feeding