Blue light after dark is disrupting your sleep and causing diseases like obesity, diabetes, neurological disease and heart disease. This is the problem and we know that exposing ourselves to artificial blue light after dark is leading to poor aging and diseases of civilization. The problem lies with interpreting the plethora of information out there from a multitude of companies selling blueblockers, on what lenses you need to be optimal.
We first need to understand what frequencies of artificial light we need to block after dark.
The Melatonin Disruption Zone
The first study that we need to look at to determine the melatonin disruption zone was published in 2014 entitled "Opponent melanopsin and S-cone signals in the human pupillary light response"
But what is melanopsin?
Melanopsin is a type of photopigment belonging to a larger family of light-sensitive retinal proteins called opsins. In humans, melanopsin is found in intrinsically photosensitive retinal ganglion cells (ipRGCs).ipRGCs are photoreceptor cells which are particularly sensitive to the absorption of short-wavelength visible light and communicate information directly to the area of the brain called the suprachiasmatic nucleus (SCN), also known as the central "body clock", in mammals.
So Melanopsin is a pigment in the eye that is vital to the communication of light to the SCN, which is used to entrain our body clocks. Pretty important for our health and sleep.
Going back to the paper in 2014 it showed that we need to be most attentive to the blue and green content within white LED lights that surround us in our homes and outside the home after dark. In a nut shell white light is standard LED house lighting, back lit LED displays on smart phones etc that contain parts of all the light spectrum. These lights are highest in blue and green light and as shown in the 2014 study were the frequencies to be most concerned with after dark for dysfunction of circadian rhythms.
In 2001 a vital study was released entitled "Action Spectrum for Melatonin Regulation in Humans: Evidence for a Novel Circadian Photoreceptor". (study link) Single handedly this is the most important study to read when it comes to understanding what frequencies of blue and green light to block.
The graph below shows the relative quantum sensitivity of the light spectrum to humans after dark. So when you buy "blueblockers" that only block blue light or not even all blue light you can now see this is not optimal and you should avoid these if you are searching for the most optimal protection after dark, these are often characterised by amber or clear lenses.
The blue spectrum of light runs from 400-495nm and the green spectrum runs from 500-570nm.
It is worth highlighting the key takeaways from the study:
- 446–477nm was identified as having the strongest effect on melatonin suppression. You need to make sure 100% from 446-477nm is blocked after dark
- Polychromatic action spectra were reasonably consistent in indicating that the spectral region between 450 and 550nm provides the strongest stimulation of circadian and neuroendocrine responses. What this means is the wavelengths of light between 400-550nm should be completely blocked for optimal melatonin secretion after dark.
- Past studies have shown that the peak wavelength sensitivity was 555nm (Rodieck, 1998). Previous data (Brainard et al, 2001) and those presented in the 2001 study do not support this hypothesis. The results clearly demonstrate that 555nm is significantly weaker in suppressing melatonin.
This is a great study for determining the optimal range of artificial light to block after dark and the study results and graph clearly suggests that the major disruption zone for melatonin is between 400-550nm with a peak between 446-477nm. After 550nm (upper green and into yellow, amber and red wavelengths) the effect on melatonin becomes almost non-existent and not a major contributor to melatonin suppression. Blocking artificial light past 550nm, based on the conclusions and results presented in this study would be unnecessary, and in our modern world we want optimal along with the ability to function in society. Darker tints that block more than necessary only impair vision, become impracticable and are not needed as shown in the scientific literature. These are common complaints we hear from people into blocking artificial light after dark.
The 2001 study is the comprehensive evidence that you need to be blocking both blue and green light for optimal sleep. (study link)
In 2001, obviously the year of green light, Wright and Lack released a paper analyzing different light wavelengths and their effect on melatonin production, when exposed after dark.
They compared 660 nm (red), 595 nm (amber), 525 nm (green), 497 nm (blue/green), and 470 nm (blue) wavelengths.
The shorter wavelengths, 470, 497 and 525nm showed the greatest melatonin suppression, 65% to 81%. The shorter wavelengths also showed the greatest circadian phase delay ranging from 27-36 minutes (in essence exposure of these frequencies of light delayed the participants falling asleep). (study link)
In 1991 a study emerged in Sleep by Horne et al. which showed that green light from 500-530nm suppresses melatonin.
In 2010, Gooley showed that mid-green light has a similar effect on suppressing melatonin as that of blue light. However during the light exposure the spectral sensitivity to the green light decayed exponentially relative to the 460nm blue light. Showing that we should not disregard blue light when looking at blocking artificial light after dark for optimal melatonin secretion.
Concluding Remarks on What Frequencies of Light to Block After Dark
Its pretty clear cut - 400-550nm needs to be blocked for optimal melatonin secretion after sunset. Less than this is sub-optimal and more than this is unnecessary.
Now we know what the melatonin disruption zone is we now have to choose blue blocker glasses to block these damaging wavelengths. The issue is there are so many blueblockers to choose from so where do we start? As a rule of thumb to block both blue and green light optimally to the 550nm range you need red lenses. Amber lenses will block blue and some green light but they will not be optimal. We want optimal.
To date we have all had discussions in groups about the best blue blocking lenses so we think its time to list some of the most popular brands and identify their blue and green light blocking capabilities. There are too many brands to analyse them all so we opted for the most popular.
They are ranked 1-7 based on what artificial light they block in line with the literature we have discussed. Those that block more have been left out of the table as wavelengths blocked past 550nm is not required in line with the literature available. Its best to be evidence based or we would all be wearing sleep masks in a dark room post sunset based on biohacking anecdotes.
Lets take a look below:
When you are looking to block artificial light after dark make sure you do it optimally. Blocking to 550nm is a must for optimal sleep and health so make sure your next pair of blue blockers do just this, no less/no more.