Longer exposure time



  • I've been trying to better understand what levels of blue light exposure will have a noticeable effect on my sleep. I'd rather not have my screen deep orange at night, if it's not completely necessary.

    From what I've read, the threshold that produces any measurable melatonin supression is somewhere around 0.35 μW/cm2. According to the f.luxometer, setting an Apple Thunderbolt 27" monitor to 4100K with f.lux, and turning the brightness to 50%, brings it well under half that threshold.

    So I figure reducing my 23" LED monitor's brightness to about 30%, and keeping the "bedtime" color the same 3400K as the "sunset" color (i.e. the "sunset only" setting), should be fine.

    The thing is that it's time dependent, and the studies I've found mentioning that threshold value only tested two hours or less of exposure. If I'm at my computer for the six hours between sunset and going to bed, do I need to use a lower value?


  • f.lux team

    The calibration on fluxometer is based on "phase shift" which is usually 40% higher than melatonin suppression, but they both are adjusted to have the same "zero" point.

    You probably want to be looking at the melanopic "SI units" in the "details" tab, if that's not what you're doing already. Some experiments will report total spectral power, but it's not as useful unless the experiment is exactly the same kind of light source. The "actinic" spectrum should be quite a bit more transferable across light sources.

    Love to know where you found the 0.35 number - sounds about right to me. When I use the parameters you specified (4100K at 30%) I get:

    Melanopic: 1.36 µW/cm2


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