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While blue light has the most impact, it's all light that has this effect. For anyone interested, I'd recommend reading this concise 4 page study on the subject

While blue light has the most impact, it's all light that has this effect. For anyone interested, I'd recommend reading this concise 4 page study on the subject.[0] The synopsis is that there's no substitute for shutting off screens 1-2 hours before bedtime. This coming from someone who not only uses f.lux but sometimes when needing to use the computer late, will adorn an old pair of sunglasses to further cut down on light from 3 monitors. [0]https://www.gwern.net/docs/melatonin/2012-wood.pdf https://www.gwern.net/docs/melatonin/2012-wood.pdf

stcredzero 11y ago
Also, I've looked at f.lux'd screens set to the reddest possible setting through a 470nm narrow band filter. There's still light at the worst color band which gets through. If you are exposing yourself to light over an extended period of time, it doesn't take much to suppress melatonin secretion. (One study found suppression at levels low as 0.5 lumen or lux -- one of those two. Either way it's not much. About commensurate with the light from a brightly lit hall coming in through the gap under your door.)
- jacobolus 11y ago
  The reddest possible setting for f.lux (almost?) entirely wipes out the blue channel, but the green primary on LCDs is also going to cause some effect. If you want you can turn f.lux into "darkroom" modes, which inverts the display and uses only the red channel.
  - stcredzero 11y ago
    Exactly. The "channels" don't emit pure light of a single frequency. There is a curve. https://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/chap12/F12-16%20RGB%20emission%20spectrum.jpg https://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot...
    - jacobolus 11y ago
      The light coming from LCD displays is different than single-color LEDs; that picture you linked isn’t a good representation of your phone/laptop. LCD displays use a “white” LED backlight (= blue LED + broader-spectrum yellow phosphor), and the various subpixels have band-pass color filters for particular wavelengths. Here’s a sketch of the basic idea: https://dotcolordotcom.files.wordpress.com/2011/10/filter-spectrum.jpg?w=1118&h=640 https://dotcolordotcom.files.wordpress.com/2011/10/filter-sp... My quick google image search isn’t turning up any particularly good SPD graphs of real recent LCDs, but if you poke around you can surely find some.
  - deleted 11y ago
    [deleted]
jacobolus 11y ago
Not really all light, but certainly at least the green and blue primaries of our computer/phone displays. In the experiment you linked, they used looking through orange-tinted safety glasses as a control, because such glasses basically filter out all of the relevant wavelengths. Not sure I’d recommend regularly using your laptop with orange safety glasses though.
- franl 11y ago
  Why wouldn't you recommend regularly using your laptop with orange safety glasses? Inconvenience or something else?

stcredzero 11y ago

Also, I've looked at f.lux'd screens set to the reddest possible setting through a 470nm narrow band filter. There's still light at the worst color band which gets through. If you are exposing yourself to light over an extended period of time, it doesn't take much to suppress melatonin secretion. (One study found suppression at levels low as 0.5 lumen or lux -- one of those two. Either way it's not much. About commensurate with the light from a brightly lit hall coming in through the gap under your door.)

jacobolus 11y ago
The reddest possible setting for f.lux (almost?) entirely wipes out the blue channel, but the green primary on LCDs is also going to cause some effect. If you want you can turn f.lux into "darkroom" modes, which inverts the display and uses only the red channel.
- stcredzero 11y ago
  Exactly. The "channels" don't emit pure light of a single frequency. There is a curve. https://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot-org/chap12/F12-16%20RGB%20emission%20spectrum.jpg https://www.ecse.rpi.edu/~schubert/Light-Emitting-Diodes-dot...
  - jacobolus 11y ago
    The light coming from LCD displays is different than single-color LEDs; that picture you linked isn’t a good representation of your phone/laptop. LCD displays use a “white” LED backlight (= blue LED + broader-spectrum yellow phosphor), and the various subpixels have band-pass color filters for particular wavelengths. Here’s a sketch of the basic idea: https://dotcolordotcom.files.wordpress.com/2011/10/filter-spectrum.jpg?w=1118&h=640 https://dotcolordotcom.files.wordpress.com/2011/10/filter-sp... My quick google image search isn’t turning up any particularly good SPD graphs of real recent LCDs, but if you poke around you can surely find some.
- deleted 11y ago
  [deleted]

jacobolus 11y ago

Not really all light, but certainly at least the green and blue primaries of our computer/phone displays. In the experiment you linked, they used looking through orange-tinted safety glasses as a control, because such glasses basically filter out all of the relevant wavelengths. Not sure I’d recommend regularly using your laptop with orange safety glasses though.

franl 11y ago
Why wouldn't you recommend regularly using your laptop with orange safety glasses? Inconvenience or something else?