What wavelength do we really need to block

  • Hi.
    So I'm confused, I'm looking at these phone filters that say they block blue light.
    Most show they block a certain percentage of blue light. 28%, 46%.. 60%.

    My questions are:

    1. does blocking anything less than 100% mean its ineffective? ie, is 60% better than 20%. Or is blue light blue light, and intensity doesn't matter?
    2. I have found that this percentage is based on a wavelength range. some say they block 60% of 380nm-450nm. Others say they block 32% of 380-500nm.
      whats the key wavelength we need to bloock?

    I've looked at some studies and it seems that ~440-480nm is key in regards to melatonin production.
    Is this true?
    Does that mean that a filter that blocks 100% of 440-480nm (assuming this is the key range) would be effective? Even if 380-420nm was coming through?


  • The fluxometer will give you a good idea of what colors those wavelengths are, use the tool to look at the "UVEX STC Orange". It's in the filter, as that's what it is, it's not a light source, so first you'll need to choose a light source similar to what you use at home, then in the filter, choose what I have in quotes.

    Heres the chart with 52 watt Incandscent, and UVEX glasses (plastics...) https://fluxometer.com/rainbow/#!id=NGDC Tungsten/GE Wattmiser 52 W frosted&filter=filter/UVEX SCT Orange

  • First rule: light you see in the morning "shifts your clock earlier" and light you see at night "shifts your clock later". Most people live a couple hours later than we would be in natural conditions, because we see light at night.

    As a rough ballpark, melanopsin "sees" light from 430-530nm and perhaps more, and at some light levels your cones also get involved, so the range is even broader. 488nm is normally regarded as roughly the midpoint of the circadian exposure.

    How much you block depends on what light you are seeing - if you are outdoors on a sunny day and you want no circadian impact, it is very hard to block enough!

    But if you are using a computer screen, we usually say you should block 90%+ to minimize circadian impact. The same goes for most residential lighting, and perhaps a little more for office lighting.

    This doesn't mean that the light will have no effect on you (it's not darkness), it just means that it will have an effect on your internal clock that's measured in single-digit minutes rather than in hours.

    Try out our https://fluxometer.com/rainbow/ site and ask any questions you have.

  • Another thing to consider is the brightness of any source of light, including a monitor or the display of a phone, phablet, or tablet or a TV. So, during the last couple of hours of your day (meaning, the last minute of your day is spent getting into your bed), I think it's wise to use the dimmest and reddest light possible from every source of light - even a computer monitor or other type of display.

  • Thank you!


    This was what I was after!

    So pretty much if I'm shopping around for a filter for my phone I want something that can block as much light in that wavelength as possible.

  • Most of the filters for phones are garbage, sorry to say - they block as much as saran wrap (which is to say they make no difference). The ones from www.lowbluelights.com are good.

  • @alex_fergus , the backlights in phones basically don't put out any light between 380-420nm, so no need to worry about it.

    The other day I bought a sheet of Rosco Orange supergel #23, which blocks nearly all the light around 440-540. It only cost a couple of dollars, should be easy to find, it's used in film & photography, for DJ lights, etc. - they have a whole range, and give the transmission spectrum charts, eg:
    https://www.rosco.com/filters/SED.cfm?titleName=S23: Orange&imageName=../images/filters/supergel/23.jpg

    I put a piece over my phone with some tape, and had enough left over to cover some lamps in my house to use at night. You'll get a lot more exposure from lamps than from your phone.

    It's quite orange, I'd say about the same as the 1900k "candle" setting in f.lux. I may get something less extreme, like the Deep Straw #15 or something.

    It's not necessary to block 100% of blue light. The effect is "dose dependent" on brightness and length of exposure. So yes, blocking 60% is better than 20% - but may be about the same if you look at it twice as long. If you put the phone screen on minimum brightness, hold it a foot away, and don't use it for more than an hour or two, it won't have any noticeable effect on most people, even without a filter.

  • Nice filter - it does allow a little bit of transmittance around 440nm, where a lot of backlights are. Still we should measure it!

    e.g., iPhone 6 has a "higher-energy" blue than a lot of other displays:
    https://fluxometer.com/rainbow/#!id=iPhone 6/6500K-iPhone6

  • Regarding "percent blocked" --

    Most models of the body's response to light are basically logarithmic, meaning "little" numbers like 20% don't matter at all, and 60% only a little bit.

    Our 3400K setting blocks about 65%, and we don't think it's enough for late at night, which is why we suggest more.

    On the fluxometer.com site we show "phase shift" based on a filter and light source and so you can get a sense - also for filters only we compute "percent blocked". For f.lux settings you have to do the math yourself.

    https://fluxometer.com/rainbow/#!id=iPad 2/3400K-iPad2

  • Thanks so much guys/girls!

    This info is great.

    Much appreciated. I'll look into getting some of that film. It could be a good idea for tvs at night!

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