For many years, the advice from scientists and experts to people of all ages has been pretty universal: using your phone before bed will mess with your sleep.
But findings from a new study conducted by Toronto Metropolitan University (TMU) and the Université Laval paint a more complicated picture of the modern nighttime habit.
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The self-reported study asked more than 1,000 adults across Canada about their bedtime screen use and sleep health, and found that overall sleep health was similar between those who used screens every night, and those who didn’t use one at all. The worst sleep came from those who used their phones only a few nights a week.
Whereas previous studies had blamed sleep disruption on the blue light emitted by phones and other LED screens—which some research says limits the body’s production of the sleep hormone melatonin—TMU researchers said those findings had not accounted for age, timing, or intensity of exposure.
Read more: 20 Things You Shouldn’t Do Before Bed
TMU Professor Colleen Carney, one of the study’s authors and a specialist in sleep and mood disorders, said other studies in the field had used experimental conditions that don’t reflect the average person’s day, and in some cases “stack the deck” to prove blue light is the culprit.
“It is true that we do have those studies, but in order to get those results, these studies usually pick young adults who are closer to puberty, which is really important, because that makes you light sensitive. And then they keep them in the lab overnight and all through the day, they’re in dim light all day long,” Carney tells TIME. “I think people have taken findings in this area and applied them much too broadly, and have not paid attention to studies that don’t find it.”
Carney says the study found that it is equally important what people do on their phone, especially “if you’re engaging in things that make it really difficult to put it down, if you’re engaging in things that are upsetting or alerting on your phone.”
The study, published in the journal Sleep Health in October, found that over 80% of participants reported using screens at bedtime in the past month, and nearly half reported using screens every night.
Carney’s study follows a smattering of similar findings in recent years that suggest the blue light may have been unfairly maligned.
The research has, for years, pointed in one direction: Blue light can disrupt sleep and potentially delay melatonin release, so limiting it is the best way to get a good night’s rest.
Several studies have found that exposure to short-wavelength blue light reduces melatonin levels, thereby negatively impacting sleep.
A 2011 study published in the Journal of Applied Physiology found a link between blue light exposure and melatonin suppression. Another 2023 study published in Brain Communications measured sleep in adolescent boys and young adult men after reading with a physical book or with a blue-light-emitting phone. The findings supported the idea that melatonin can be suppressed by blue light, but also found that the negative effects could be mitigated if the phone was put away at least one hour before bed. An April 2025 study published in the journal Life underscored that blue light disrupts circadian rhythm and found that red light was a better alternative.
Other studies found a strong link between phone use and poor sleep quality, but could not determine causation.
A 2016 study published in the journal PLOS ONE and covered by TIME found a strong link between phone use before bed and poor sleep, while making no conclusions about causation. The 30-day study measured the screen time of 653 adult participants across the United States.
“We can’t exclude the possibility that people who just can’t get to sleep for some unrelated reason happen to fill that time by using their smartphone,” one of the study’s authors Dr. Gregory Marcus, told TIME in 2016.
In a 2024 National Sleep Foundation expert panel made up of 16 experts in sleep and pediatrics, published a consensus statement saying that screen use in general impairs sleep health in children and adolescents, but primarily due to content. The panel did not reach consensus on whether exposure to blue light from screen use before bed can impair sleep in adults.
A March 2025 American Cancer Society study of over 122,000 participants found that daily screen use was associated with later bedtimes and about 50 minutes less of sleep each week.
Dr. Alex Dimitriu, a psychiatrist and sleep medicine doctor in Menlo Park, Calif., calls the study “fascinating, because it goes against a very large established body of research which suggests a clear effect on sleep quality from screen use,” citing the 2025 American Cancer Society study as an example.
“The authors do acknowledge some interesting findings [including] that causality cannot be clearly determined from this study. And it is possible that good sleepers either use phones or they don’t, while poor sleepers aren’t sure what to do,” Dimitriu tells TIME.
In Dimitriu’s professional opinion: “Screens are not good for sleep.”
“I can stay up [for] hours scrolling through news articles, blogs, and social media posts. If I try reading a book, I’m out within 10 minutes. My patients feel the same,” he says. “Screens, besides being bright, are just too interesting.”
The TMU research is not the first of its kind to suggest that blue light may not be the major factor in sleep disruption.
Several other studies also indicate that research on blue light and sleep is mixed. A 2022 review in Frontiers in Psychology examined 24 studies to answer this exact question in young adults. One in five of the studies reported decreased sleep quality after blue light exposure, while one in three reported decreased sleep duration. Fifty percent of the studies showed decreased tiredness, consistent with blue light increasing alertness and improving cognitive performance during the daytime.
“[I]n general, the specific effects of blue light exposure seem still to be a murky field and more investigations are needed before final firm and evidence-based conclusions can be drawn,” the study reads, although the researchers do say that blue light “might also have negative effects such as the decrease in sleep quality and sleep duration, which might worsen an athlete’s physical and cognitive performance and recovery.”
The researchers at TMU note that younger people may be more vulnerable to the melatonin-suppressing effects of light, and many studies have found that nighttime exposure to light can particularly affect children and adolescents, not the adults that TMU’s study focuses on.
“There may be reason to be cautious about excessive blue light exposure in the evening for teens as puberty increases light-sensitivity,” Carney said in the paper’s release. “As we age, we are not as light sensitive and there are age-related effects of the eye that make light less disruptive.”