Blue Light Revisited


Blue light was the subject of a blog post here a few weeks ago. If you missed it you can access it here:

We are finding more and more information on blue light and it’s effects and I wanted to go over a few more studies looking at it.

First, a report discussing the effects of shorter wavelength (blue) light. In the first, blue was compared to green. Exposure to blue light induced a 2 fold greater circadian phase delay than green light. That means that both green light and blue light are resetting your circadian clock. The total amount of reset is dependant on intensity and duration. [1]

Another study found similar results, comparing blue, blue-green, green, red and amber with no light controls. Red and amber were found to not produce any significant difference over control. Blue and green again increased the onset of melatonin. [2]

Another study looked at subjects and their melatonin secretion, as well as perceived sleepiness. Subjects were given either blue, green, or no light after 1.5 hours of light, followed by 2 hours of dark. Light exposure then followed for two hours. 2 more hours of normal light exposure and then sleep. Here a jpeg to get all of that across.



Researchers found that melatonin was decreased in the blue and green groups, but to a lesser extent in the green group. Blue light also increased heart rate slightly but significantly, to the tune of 4 beats per minute. Core body temp also remained higher in the blue light group over the green and light groups. It appears that blue light increases sympathetic tone. That means that your fight or flight systems are a bit more active in the presence of blue light. [3]

Another study found that REM sleep was reduced by about 10 minutes per night when people were reading on E-readers than a regular book.[4] REM sleep seems to be linked with mood. [5]

Another study looking at 4th graders and 7th graders found that these students had less sleep when sleeping with electronic devices and/or TVs in their rooms than those who didn’t. [6] This of course makes sense. I’m more likely to stay up later and fight off sleep if I’m on the TV or reading than if I just go to bed. Maybe we as a society needs to be more wanting of sleep and not to be entertained.

Lack of sleep is bad for weight, depression, blood sugar, cardiovascular health and a whole host of other things.

Glasses made to filter out blue light seem to help, as noted in one study. [7] I made mention of these in the previous post.

In another study done with glasses to filter out blue light in adolescent males, researchers found that melatonin was increased if the blue filter lenses were used. [8] The authors in this study noted that no circadian rhythm was changed, but they hypothesized that one week, the length of the study, may not have been long enough.

These types of glasses may be useful, especially those that are working night or swing shifts. They can be purchased fairly inexpensively too. Plus you don’t typically have to lug them around everywhere. You can keep them at you desk or by your bed.

Naturally it’s better to just avoid computer and phone use before bed, but that can be very difficult, especially if the job demands it. Try some glasses out or other forms of entertainment at night, like sleep or reading a book.



1.Lockley, Steven W., George C. Brainard, and Charles A. Czeisler. “High sensitivity of the human circadian melatonin rhythm to resetting by short wavelength light.” J Clin Endocrinol Metab 88.9 (2003): 4502-4505.

2.Wright, Helen R., Leon C. Lack, and David J. Kennaway. “Differential effects of light wavelength in phase advancing the melatonin rhythm.” Journal of pineal research 36.2 (2004): 140-144.

3.Cajochen, Christian, et al. “High sensitivity of human melatonin, alertness, thermoregulation, and heart rate to short wavelength light.” The Journal of Clinical Endocrinology & Metabolism 90.3 (2005): 1311-1316.

4.Chang, Anne-Marie, et al. “Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness.” Proceedings of the National Academy of Sciences (2014): 201418490.

5.Cartwright, Rosalind, et al. “Role of REM sleep and dream affect in overnight mood regulation: a study of normal volunteers.” Psychiatry Research 81.1 (1998): 1-8.

6.Falbe, Jennifer, et al. “Sleep Duration, Restfulness, and Screens in the Sleep Environment.” Pediatrics (2015): peds-2014.

7.Wood, Brittany, et al. “Light level and duration of exposure determine the impact of self-luminous tablets on melatonin suppression.” Applied ergonomics 44.2 (2013): 237-240.

8.van der Lely, Stéphanie, et al. “Blue blocker glasses as a countermeasure for alerting effects of evening light-emitting diode screen exposure in male teenagers.” Journal of Adolescent Health 56.1 (2015): 113-119.