People always say, “stay away from computer screens before you go to bed,” but what exactly is wrong with nighttime smartphone scrawling?

According to a new study in the journal Sleep, the problem is cyan, the greenish-blue color commonly emitted from smartphone displays and computer screens.

Scientists from the University of Manchester have recently discovered that high levels of cyan light emitted from a visual display can decrease your body’s production of melatonin, thereby making you less sleepy and more awake. Armed with this knowledge, they have created a new type of screen that can help ward off many people’s sleepless nights.

As part of their study, the researchers documented how high levels of cyan light made participants in the trial feel more alert than lower levels of the color. They backed this up by looking at their melatonin levels, the “sleep hormone” produced by our body when it thinks it is night, as they were exposed to different levels of cyan light. The more cyan light, the less melatonin they found in their spit.

“This outcome is exciting because it that tells us that regulating exposure to cyan light can influence how sleepy we feel,” Professor Rob Lucas, of the University of Manchester, said in a statement. “Our study also shows how we can use that knowledge to improve the design of visual displays. We built our melanopic display by adapting a data projector, but we would expect that this design could be applied to any type of display.”

The researchers also unveiled new technology, called a “melanopic display,” that allows users to control the levels of cyan light emitted from their screen. In conventional computer and TV displays, cyan is created by combining green and blue light. This new device also has a cyan light that can be adjusted at will. They even argue it makes the image quality sharper too.

“We built our melanopic display by adapting a data projector, but we would expect that this design could be applied to any type of display,” added Professor Lucas.

“Such displays could, for example, help phone obsessed teenagers to fall asleep, or support alertness in people who need to use a computer at night.”