August 2017, rev. October 2019
Overhead lights lead to computer vision syndrome (CVS) in programmers: blurry vision and trouble focusing the eyes. CVS affects 90% of people who spend more than three hours on the computer daily.
Lighting above but in front interferes with looking straight. Same with lighting that is far and low enough to enter the line of sight.
Lighting above but behind seems ok. So does underhead lighting that doesn't point towards the eyes.
Besides bad lighting, air conditioning and air fans can cause harm too. Blowing air into programmers' eyes leads to dry eyes.