Smartphones deliver light to users through Light Emitting Diode (LED) displays.
In this light, blue light has the most potent effect on sleep and mood. So, it has been suggested that if blue light could be suppressed, the harmful effect of light from smartphone screens could be significantly reduced.
This study, funded by Samsung Display in South Korea, looked at this question.
This is the first controlled study of the effects of exposure of blue light from smartphone LED displays at night on humans.
A randomized, double-blind, cross-over, placebo-controlled design was used.
By “cross over” we mean that the same subjects were exposed to one type of light and then crossed over to being exposed to the other type of light. So, the same subjects received exposure to both types of lights. But the order in which they received one type of light first or the other was random.
The evaluations were done by admitting the subjects to the research unit twice--for three days at a time.
Two types of smartphones were used. One type had a conventional LED display with the full range of light. The other type had an LED display that has been newly developed by the sponsor of this study, Samsung Display. This type of smartphone suppresses the blue light portion of the spectrum of light.
Was this study blinded? Yes, the two types of smartphones were indistinguishable from each other with the naked eye because the researchers used other wavelengths to mimic blue light in the smartphones in which blue light was suppressed.
Persons with any mental disorder, substance use disorder, or primary sleep disorder, or those who were on any psychotropic medication were excluded from participation in this study.
Each subject played smartphone games with either a conventional LED smartphone or a suppressed blue light smartphone from 7:30 to 10:00 pm. Evaluations were done.
A few days later, they were readmitted, but given the other type of smartphone to play with, and the evaluations were repeated.
The evaluations included changes in serum melatonin levels, cortisol levels, body temperature, and various psychiatric measures of mood, sleep, fatigue. Their scores on the video games they played were also monitored. A Continuous Performance Test was also used.
Twenty-two participants completed both phases of the study.
Use of smartphones without blue light suppression was associated with statistically significantly decreased sleepiness, decreased changes on the Profile of Mood States questionnaire that would be expected with sleepiness, and increased commission errors on the Continuous Performance Test.
Other changes (serum melatonin and cortisol levels) were not statistically significant.
Use at night of LED smartphones without blue light suppression may impair sleep and cognitive performance (increased commission errors).
All patients with sleep-related complaints should be asked to avoid or minimize use of computers, tablets, or smartphones in the few hours prior to bedtime.
But given that these devices have become an indispensible part of our lives, this is easier said than done.
So, we should advise our patients that when use of computer, tablet, or smartphone is unavoidable, blue light suppression should be used.