Now that we’re nearly 20 years into the smartphone era, most of us have heard this basic tip for getting better sleep: set your phone down well before going to bed.

The theory is that the blue light radiating off your phone will signal to your brain that it’s time to be active, not to shut down.

Put down the phone?

Over at the Stanford Center for Sleep and Circadian Sciences, Jamie Zeitzer had a feeling something about that advice didn’t add up.

“There is a bit of misperception out there about how important screen light is,” says Zeitzer, who is best known for hacking jet lag with a 2016 sleep science study (more on that in a minute). His team found that the blue light emanating from your smartphone makes almost no difference in the quality or duration of sleep for most people. Something else does in a major way.

But first, Zeitzer says, its important to understand the systems that let our brains receive light. One of those systems enables you to see objects. The other is a set of cells in the retina that project many different things that are around the image but unrelated to it, including light. These cells arent asking how bright the light is, but rather, how bright it is compared to light we’ve been getting, Zeitzer says. And that lux measurement the amount of light hitting a surface is all relative.

For a person who has been outside much of the day, taking in sunlight between 10,000 lux on a cloudy day and 100,000 lux on a bright day, getting 30 lux off a phone screen “does nothing to your brain,” he says.

Studies that correlate sleep issues with bedtime phone use are often testing people who have been indoors all day, where lighting ranges from 50 to 500 lux. If youve spent the day at home, looking at a phone before bed can indeed make a difference.

If youve 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. It’s that you’re on your phone using apps or social media or entertainment that has been gamified to make sure you don’t go to sleep,” he said. “You’re doing things that psychologists have developed to make sure you’re on it as long as possible.”

And the longer you stay awake, the greater your fatigue and its impact on mental health. Theres an element of social isolation and loneliness people feel if youre up late at night,” Zeitzer says. “It’s 3 a.m., there’s nobody else around. Is that an environment that is conducive to being anxious and depressed?”

Getting outdoors not only helps you sleep, it makes you feel better in the moment. So much so, Zeitzer is experimenting with a 20-foot-long virtual window in the lab.

Were trying to figure out, what is it about being outside, from a visual perspective, that makes us feel better, Zeitzer said.

Dr. Jamie Zeitzer and postdoctoral fellow Maira Karan are experimenting with a 20-foot-long virtual window to see if technology can simulate the benefits of natural light indoors at the Stanford Center for Sleep and Circadian Sciences, Wednesday, Sept. 18, 2024, in Palo Alto, Calif., . (Karl Mondon/Bay Area News Group)

Wake up with light

San Jose State sleep scientist Cassie Hilditch has spent 20 years studying how to help emergency workers and other late-night shift workers cope with fatigue. Short naps during night shifts can help improve performance, she says, but its really important to expose yourself to bright light as soon as you wake up. (If you’re waking after dark, find a therapy lamp that can emit as much as 10,000 lux.)

“Light has the ability to make you feel more alert the moment youre exposed to it,” Hilditch said.

And whether youre resetting your body clock for a night shift or bracing for jet lag, changing time zones and increasing light exposure can help.

“You can use light to manipulate the timing of your sleep,” Hilditch said. “If you want to delay your sleep if you’re on the East Coast and traveling to the West Coast you can start preparing by exposing yourself to light later into the evening and avoiding light in your usual wakeup hours. The opposite is true, if you’re on the West Coast. What I do in preparation is try to avoid any light in the evenings and then expose myself to really bright light in the morning.

Most peoples circadian rhythms can only shift about an hour each day. So shifting your bedtime and light exposure a half-hour each night before a coast-to-coast flight can help.

In the Stanford sleep lab, Zeitzer discovered another light-related tip for curing jet lag. Theres the advice youve probably heard before: “Get bright light exposure when your flight lands and stay awake all day, even if you didn’t get a good night of sleep, he says.

This part, though, may be new to you: Set a flashing light to go off three hours before your alarm clock rings, Zeitzer says, if you’re going from the West Coast to the East. Even though your eyelids are closed, the cells in the retina can transmit the light information to the circadian system, and the gaps of darkness between light flashes allow the eyes to regenerate, so you can continue sleeping while your brain is recalibrating.

His testing results? A flashing light while sleeping elicited a nearly two-hour delay in the onset of sleepiness.

A Stanford student-led company, LumosTech, has licensed a patent for such technology and now sells eye masks with flashing lights ($250) that are timed to help reduce sleepiness upon waking up.

Light and happiness

Each fall, Californians turn their clocks back one hour, a change that signals the beginning of winter, longer nights and shorter days.

For many, it can trigger seasonal affective disorder (SAD), an illness that shares many symptoms of depression, including sadness, listlessness and sluggishness, according to a Harvard University study. Around 5% of Americans report experiencing SAD during 40% of the year.

There’s no cure-all, but light therapy essentially using a therapy light for 20 to 30 minutes to amp up your light exposure in the morning has proven remarkably effective, says Harvard Medical Schools Richard S. Schwartz, who found light therapy improved SAD symptoms for 40 to 60% of the people in his study.

Of course, good sleep habits exercise, sunshine, diet, a bedtime routine play an important role for everyone. Whether youre trying to fall asleep or dealing with 3 a.m. wakefulness, swapping out a book for your phone is an excellent idea.

Lesther Papa, a San Jose State assistant psychology professor, uses a Casper glow light with a 45-minute timer. He likes to read during those 45 minutes as the gradually dimming light signals to his body that it’s time for sleep. The light works in reverse in the mornings, gradually turning on 45 minutes before his alarm.

“It feels like sunlight is already coming in,” he says. “When you wake up, the first thing you shouldnt be doing is going to your phone again. Let yourself get acclimated to your natural light surroundings.”

So what about artificial light? Were surrounded by lightbulbs of every sort, from LEDs to CFLs and smart bulbs that glow in every color from blues and greens to five shades of white.

Interior and architectural designer Megan Afifi began studying the effects of colored light on mood as an undergrad at Pepperdine University. What she found was that lighting in warm shades (yellows, for example) and cool hues (blues) can have a dramatic impact on mood, and the effects on cognitive performance are task dependent. Reaction times are faster in warm lighting, but creative intelligence is higher in cool lighting, she says. And extremes an all super warm or all super cool environment make people feel uncomfortable.

Afifi favors smart lightbulbs, whose color and warmth can be set from your phone, bulb by bulb, and can mimic, say, morning light or a sunset glow or coordinate with home decor.

“Dusk and dawn are very warm, golden sunlight, she says. That’s why sunlight is so helpful to get you going in the morning.