Sandee LaMotte wrote this article in CNN:

Sleeping for only one night with a dim light, such as a TV set with the sound off, raised the blood sugar and heart rate of healthy young people participating in a sleep lab experiment, a new study found.

The dim light entered the eyelids and disrupted sleep despite the fact that participants slept with their eyes closed, said study author Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine at Northwestern University Feinberg School of Medicine.

Heart rate typically drops at night, slowing down as the the brain is busy repairing and rejuvenating the body. An elevated heart rate at night has been shown in numerous studies to be a risk factor for future heart disease and early death.

High blood sugar levels are a sign of insulin resistance, where the body stops using glucose properly and the pancreas goes into overdrive, flooding the body with extra insulin to overcompensate until it eventually loses its ability to do so. Over time, insulin resistance can ultimately lead to Type 2 diabetes.