Is it bad to sleep with the light on?

Yes, moderately. Light suppresses melatonin, fragments sleep architecture, and even dim ambient light during sleep has been associated with worse glucose regulation and cardiovascular measures. Darkness or an eye mask is better.

Even low-level light during sleep has been associated with reduced heart rate variability and worse next-morning insulin sensitivity in controlled studies.

If a light is needed for safety, a dim warm-toned light placed low and away from eye level is less disruptive than an overhead or blue-toned one.