Knowledge

Late work should not quietly turn the room back into daytime.

If someone chooses to work for two more hours at 11:30 p.m., visibility still matters - but the state should remain explicitly different from daytime focus.

“Proper light at the proper time” is more precise than “healthy light.”

The useful question is not whether a lamp is healthy. It is what light reaches the eyes, when, for how long, and in what context.