Light-sensing neurons in the retina that signal the central clock are primarily located in the bottom half of the retina and view the upper visual field.

“these cells in our eye, these neurons that signal the central clock, reside mostly, not exclusively, but mostly, in the bottom half of our retina, and because we have a lens in front of our retina, and because of the optics of lenses, that means that these cells are actually viewing our upper visual field,”

“I should mention that the reason overhead lights are problematic is the same reason why sunlight is so great early in the day, which is that the cells, that is, the neurons, that can wake up your brain and body through activation of the circadian clock reside mainly in the bottom half or 2/3 of your neural retina and the way the optics of your eyes work is that the cells on the bottom half of your eye view the upper visual field.”

“These cells in our eye, these neurons that signal the central clock reside mostly not exclusively, but mostly in the bottom half of our retina. And because we have a lens in front of our retina and because of the optics of lenses, that means that these cells are actually viewing our upper visual field. This is probably not coincidental that these cells were essentially designed to detect sunlight, which is overhead, of course. So if you want to avoid improper activation of these neurons, it's better to place lights that you use in the evening low in your physical environment. So on desktops or even the floor, if you want to go that way as opposed to overhead lights.”