English summers (and winters)..



  • So now we all know, no blue light, or progressively smaller amounts, in the 2-3hrs before bedtime which suggests to me an ideal day being made up of get up with the sun, spend 12hrs in daylight 6500k, 3hrs in a warmer light (why can't you buy lamps lower than 2500k? - incandescence were only 1700k) and then 9hrs sleep (optimum amount according to a US Army study). Which sounds a lot like living near the equator. So were our body clocks set then, still running now more or less on the same basis? Humans did spend an awful long time living there compared to anywhere else so that might account for it.

    So I have my smart bulbs with daytime and evening settings. But what do you do with english 13/14/15/16hr days?
    Even if the last few hours of sunlight are a lower colour temperature (anyone have any data on that?) still can't get 2-3hrs warm light before bedtime.

    And engish winters.... 8/9/10/11 hr days. Turn the temperature up to 6500 for 4/3/2/1 hr respectively?

    Anyone played around with this, seen any scientific research at a more granular level?


  • f.lux team

    I think the main question you are asking is about day length, and we know some of the pieces. Overall we should think of how much "bright light" we see, and how much "dim light/darkness" we see.

    For instance, is your living room at night "bright" to your body, or is it "dim"? In nature we only see a couple hours of "dim light" during twilight, and the day is very bright and the night is very dark (a million to one). So our modern tendency to see hours and hours of dim light may be a bit off.

    Humans have evolved somewhere below 40N latitude so if you live >50N, there is a decent argument for trimming the day a bit on the longest days of the year (closing your blinds in the early morning and even for the last hour of light of the day). If you don't, generally you will just sleep less and have less melatonin during the summer months. So it may make you a little irritable or something like that in June-July.

    During the winter, some people in natural conditions would sleep ("segmented sleep") in two parts: they might fall asleep earlier in the evening if they were tired, then wake up and go back to sleep again. I'm not sure most modern people are comfortable with this pattern -- they perceive it as "bad sleep" if they wake up, and so if you increase the duration of darkness like this you might find it takes some getting used to. But I'm also interested in the theory that this extended darkness may be protective of cancer and drive other kinds of seasonal effects, so I think we should spend more effort trying to understand it. Might not fit the modern pattern so well.

    Generally, my mental model is about trying to figure out how long your "bright light" photoperiod is (and when it is), and how much truly "dim light" (<5 lux, or using a very dim screen) or darkness you see, and see how it makes you feel at different times.

    I have become somewhat opposed to using the same, fixed "summer" schedule all year round, as is the modern trend - people light their houses at 50-100lux at night until right before bed, and it's too much. It buries a lot of the seasonal signals that people would have otherwise.

    But this question about what our lighting "should" be is a bigger project, and it may change a lot of things about what we do, when. For instance, how would it feel if you worked fewer hours in the winter? How would you feel if you woke up in the middle of the night for a couple hours? etc.