Approximate wavelengths, in nanometers (nm):
[Strongly] suggested pre-reading: Artificial light and circadian rhythms: blocking the blues and The Hot Blue-Blocker Experiment
Study 1 tested the effects of different wavelengths of light exposure (compared to total darkness) from midnight til 2 AM on melatonin suppression on night 1 and melatonin onset on night 2 (Wright and Lack, 2001). Note: there was no light on night 2.
On night 1, they found that 470 (blue), 497 (blue/green), and even 525 (green) suppressed melatonin, ranging from 65 to 81%.
However, remarkably, on night 2 those same wavelengths had a carry-over effect, delaying melatonin onset by 27 to 36 minutes!
This is why lens color of your blue blockers matters. Orange lenses block blue, although blue/green and even green can still have a detrimental impact. Redder lenses more effectively block in the green range.
If you get up to pee or whatever in the middle of the night, it might be prudent to rock your blue-blockers and/or have a lamp with a red bulb.
The following graphs show you how much light is blocked by different lenses – remember, we want as little transmission up to around 525 nm (according to study 1 [above] and study 2 [below]).
However, for a quick and dirty test you can do at home, the people at Spectra479 put this together:
Normal gray-lensed Ray-Bans block about 85% of all visible light. Cool for blocking UV, but you’re still getting about ~15% of blue and green light. That’s too much.
Spectra479s block 99.8% of 450-510nm, which fully encompasses blue to blue-green.
Study 2 demonstrated the importance of getting LIGHT in the morning (Wright et al., 2004). Conditions were similar to study 1, although light exposure was in the morning on days 1 and 2 and melatonin onset was measured in the evening prior to the study and on the second night. Compared with the control condition (top graph), red light in the morning had no impact on melatonin levels in the evening (middle graph) whereas blue light significantly increased them (bottom graph).
Blue-to-green light in the morning also significantly advanced the phase of melatonin onset whereas red light had no effect.
The ratio of blue-to-red sunlight is higher in the morning than in the evening. THIS SHOULD TELL YOU SOMETHING ABOUT THE IMPORTANCE OF CIRCADIAN RHYTHMS. These things aren’t coincidences.
These aren’t isolated findings (eg, Brainard et al., 2008).
Some companies have gotten wise to this and have made blue-light devices for use in the morning (I like Syrcadian Blue because it's highly portable, can clip onto your car’s visor, your computer monitor, etc.).
Some studies suggest blue and green light at night is the most suppressive (eg, Brainard et al., 2001), which is why blue-blockers with red-tinted lenses may have a slight edge over orange lenses. In the figure below, peak melatonin suppression is with blue light, but there’s still significant suppression in the green range:
Don’t get me wrong, orange lenses still work (compared to yellow lenses in this study and regular sunglasses in this study). Redder lenses may be more important later in the evening, if your circadian rhythms are in the gutter, or if you have other health problems.
There are many options for blue light blocking glasses in the evening – I’d just check the transmission spectra (or use Spectra479's test) to make sure your blocking some green as well.
Our modern #context sucks for most people. Optimally, we’d be able to get outdoors every day and avoid any light other than moonlight, candles, and bonfires at night. But in reality, just about no one can afford to do this. Ergo, in my opinion, LIGHT is just a really easy hack.
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