If bedside lamps are too low, light hits the mattress and not your book. Too high, and it shines in your eyes instead of on the page. Wrong height means you squint, adjust constantly, or give up reading in bed altogether.
Ideally, the bottom of the lampshade sits roughly at your chin or shoulder level when you’re sitting up in bed. That way, the light spreads over your book without blinding you. The switch should also be easy to reach without stretching.
A few centimetres adjustment—different lamp base, stacked books, a small wall bracket change—can make bedtime reading much more comfortable.