Blogger Titania Jordan tosses and turns for hours each night, and she thinks she knows why.
"From about 7pm 'til midnight, I am in front of a screen. I'm on the computer, I'm on my mobile device," Jordan said.
Researchers know that light suppresses melatonin, a hormone that regulates sleep. And now with texting, emailing, or TV, we may be shifting our own internal body clocks, our circadian rhythm.
Now something new: Doctors are raising a red flag about blue light, the kind emitted by energy-efficient light bulbs and electronic gadgets.
"We know that blue light has the greatest propensity to alter circadian rhythms, and yet nowadays, it seems that blue is the color du jour," said Dr. Nathaniel Watson with the American Academy of Sleep Medicine.
Doctors say even dim light can be a problem.
"We've done a number of studies to show that light levels that you would be normally exposed to in the home in the evening -- for example from a bedside lamp -- are very easily capable of shifting the body clock," Harvard researcher and author Dr. Steven Lockley said.
And pay attention, your health may be at risk. Studies link blue light and poor sleep to depression, diabetes, obesity and heart problems. Now they've added cancer to that list too.
"Shift workers have been found to have about a 50 percent to 60 percent increased risk of cancer, particularly breast cancer in women and prostate cancer in men," Dr. Lockley said.
Doctors say power down two to three hours before bed.
"If you must have screen time before going to bed, then limiting the amount of light that's emitted from the screen would be helpful, so you can turn down the brightness," Dr. Watson said.
Exposing yourself to lots of bright light during the day can also help you get the sleep you need at night. Doctors say the bright light keeps you alert and helps your body clock reset each night.