If you've spent the day outdoors, the brightness of the phone makes no impact, Zeitzer says. It's what you're doing on that phone that matters. "At that point, it's not the blue light keeping you up.

The changes, which are subject to regulatory approval, would extend Arca electronic exchange hours from 1:30 a.m. ET to 11:30 p.m. ET Monday through Friday, or 22 hours a day, 5 days a week.