I use flux and I know the importance of eliminating blue wavelength before bed. What I don't understand is the need to eliminate green, and this graph on your site doesn't help much in understanding that: https://i.imgur.com/fHJKxWA.png (rehosting on imgur for short URL)
I don't know what the grey area is, and there are no axis so I am unsure what this graph is even showing me. Also, wouldn't eliminating "orange" light be just as important (according to the graph you provided), since it seems to follow the same path as green?
Everything else makes sense on the page, it's the graph that threw me.
In simple terms, both blue and green light contribute equally to circadian interruption.
The graph itself is a comparison of spectral power distributions among several light sources. It's basically the signature of the light source, showing relatively how much of each color is produced in comparison to all the other visible wavelengths.
The gray area is melanopic sensitivity. This is the light that the ipRGCs[0] in the eyes are sensitive to, which provide input to the circadian rhythm. The peak is approximately 480-490 nm, but the overall sensitivity covers both blue and green wavelengths.
There's a great article on the blue/green concept by Ian Ashdown [1].
If you use the f.luxometer tool [2], developed by the f.lux team, you will see that same curve.
EDIT (for clarity): In the graph you linked, ignore the color of the lines. That is just to distinguish the different light sources. Just pay attention to the intensity of the wavelengths on the x-axis. The y-axis scale is 0 to 1, as this graph is normalized, so hardly necessary to show. Let me know if I can help clarify this further!
"Orange," "green," etc. in those graphs are just different models of lightbulbs. (Maybe using patterns - dotted, dashed, etc. lines - would have been clearer than overloading color.) For colors, look at the frequencies on the X-axis.
Anyway, the trick is that photoreceptor cells are sensitive to a range of frequencies, with weights centered on a particular color, and return a single floating-point output. So your blue cones cannot distinguish bright green and dim blue - that's only calculated by taking the input of the green cones into account, too. See https://i.stack.imgur.com/5snTb.png for what each cone's sensitivity looks like (in this graph, lines are light received by each cone, and the colors are semi-meaningful). If the goal is to not stimulate the blue cones at all, you need to emit as close to pure red light as possible. The wavelength of your light as measured by the single average or dominant color isn't as interesting as the spectrum of all light it emits and how much that overlaps with blue sensitivity.
One thing to point out is that the circadian rhythm is (largely) not directly influenced by the cones or rods (to our current knowledge). It is a third set of photoreceptors, the ipRGCs, which detect blue/green light and provide input to the circadian rhythm in the pineal gland/suprachiasmatic nucleus. The gray area is the sensitivity of the ipRGCs.
Also, that's a good point about the colors vs. dotted/dashed lines. I'll look into that, thanks!
We know the ipRGCs receive cone and rod inputs and that non-melanopsin responses (from rods and cones) drive a lot of the reaction at lower light levels.
> If the goal is to not stimulate the blue cones at all, you need to emit as close to pure red light as possible.
Ah, I gather this is why you use red lights at night when you don’t want to disturb your night vision as opposed to a light with any green component (yellow, orange, etc).
One thing your rods (lower light receptor cells that are more dominant 1deg+ off the exact area of gaze) have peak sensitivity at the 'green' range of the spectrum. So, green will nuke your night vision whereas red (and to a lesser extent Amber) will leave your rods dark adapted.
Is there real evidence / studies that show blue light is bad at night?
I can fall asleep in minutes after using computers/phones/tv with no (aparent) issues at all. My wife and kid too.
I don't know what the grey area is, and there are no axis so I am unsure what this graph is even showing me. Also, wouldn't eliminating "orange" light be just as important (according to the graph you provided), since it seems to follow the same path as green?
Everything else makes sense on the page, it's the graph that threw me.