You detect light to know when to wake up or something is happening. Totally blind people also have the mechanism and why they know when it is morning (unless they are missing the organ). I am sure there are other reasons.
In 2017, over 7 million Americans had vision loss or blindness based on best corrected visual acuity in their better-seeing eye (using autorefraction).
Vision Loss: best corrected visual acuity 20/40 or worse.
Blindness: best corrected visual acuity 20/200 or worse.
Total blindness is the complete lack of light perception and form perception, and is recorded as “NLP,” an abbreviation for “no light perception.”
Few people today are totally without sight. In fact, 85% of all individuals with eye disorders have some remaining sight; approximately 15% are totally blind.
You detect light to know when to wake up or something is happening. Totally blind people also have the mechanism and why they know when it is morning (unless they are missing the organ). I am sure there are other reasons.
Removed by mod
Most blind people have some vision
Complete blindness is pretty rare I think
https://www.cdc.gov/visionhealth/vehss/estimates/vision-loss-prevalence.html
https://www.afb.org/blindness-and-low-vision/eye-conditions/low-vision-and-legal-blindness-terms-and-descriptions