"Exposure to blue light" means being in contact with the type of light that is emitted by electronic devices such as smartphones, computers, and tablets. Full definition
Exposure to blue light from the screens of computers, smartphones and tablets can inhibit melatonin production, which makes it much harder to fall asleep. (blog.fitplanapp.com)
Too much exposure to blue light at night reduces your body's production of melatonin, a hormone that helps you fall asleep. (digitaltrends.com)
It uses specialized filters to limit exposure to blue light. (goodereader.com)