Morning and evening sunlight exposure, while avoiding bright light at night, is crucial for coordinating cellular activities and maintaining regular biological rhythms.

“We do need sunshine. Why do we need sunshine? Because it sets our rhythm into a regular state where the genes in all of our cells can be expressed at the correct times. We're sort of a factory of cells, if you will, and that factory can only run properly if it knows when certain things should be active and when certain cells should not be active. And the best way to coordinate all of those activities of all the cells is to get sunshine in your eyes in the morning and again in the evening, and not to get too much bright light in your eyes in the middle of the night.”