If you like your room to be pitch black when you hit the sack for the night, it turns out that you’ve been right all along.

A study shows that sleeping with even a moderate amount of light from a TV, electronics, a streetlight, or any other source may have detrimental effects on your metabolic and cardiovascular health.

A team of researchers led by Dr. Phyllis Zee at Northwestern University studied 20 people to see how 100 lux of artificial light affected half of the healthy adults while they slept.

The 10 people that were exposed to artificial light while they slept had elevated heart rates during the night and had increased insulin resistance in the morning.

The second finding means that those people had more trouble than the others getting their blood sugar into what would be considered a normal range.

A lot of what happens while we sleep is still a mystery but this study seems to be a good start into figuring out how light affects us when we’re getting rest.

Sleep tight, my friends…