Sleeping with the television on increases the risk of obesity by a third.
A new US study has found that light exposure from TVs, smartphones and lamps can disrupt sleep, which can have a harmful impact on key hormones and physical activity when you wake up.
The research of nearly 44,000 women showed that those who kept a light or TV on while they slept were 33 percent more likely to be obese than those who didn't.
Writing in the JAMA Internal Medicine, researcher Dr Dale Sandler, from the National Institute of Environmental Health Sciences in North Carolina, said: "Exposure to artificial light at night while sleeping was significantly associated with an increased risk of weight gain and the development of obesity.
"In particular, sleeping with a television or a light on in the room was positively associated with gaining 5kg or more.