Let’s say I want to boost circadian amplitude as much as I can. What light/dark schedule should I put myself on?
This is a very tough question to answer experimentally, given how many possible light/dark schedules there are (infinite) and how expensive experiments like this can be (near infinite). But mathematical modeling can give us a clue of what might happen.
Let’s say I fix myself to a 24 hour day and light schedules that are either bright light or pure darkness. I can generate a bunch of different light schedules of different lights-on duration and light brightness (in units of lux) during the lights-on period, then run these schedules through a mathematical model of the circadian clock on repeat. When I do this, here’s what I see happen to the model’s average circadian amplitude:
In other words, brighter light and 8ish hour days seem to be best for maximizing amplitude, though a lot of day durations are just about equally good, especially when the maximum brightness is lower than 10,000 lux. It also seems better to have a very short day versus a very long day, possibly because very long days can’t help but have light hitting the parts of the day where light exposure squishes amplitude in the model.
How important is that 24 hour day? Now let’s try a range of periods, where the duration of light and dark is equal (e.g. for a 4 hour period, we have 2 hours of light and 2 hours of dark), alongside a range of brightnesses. What’s best when we do this?
Behold: To get the most amplitude (on average) out of a mathematical model of the human circadian clock, you need a period roughly like the human circadian clock. Interestingly, periods slightly longer than what humans can entrain to, like you might see in a forced desynchrony protocol, appear to squash amplitude quite a bit.
What’s this mean for normal people? Models suggest that the best way to boost your circadian amplitude is to have very bright days and very dark nights, with about 5-15 hours of light per day. Brighter days should boost amplitude more than dimmer days, and your days should be about 24 hours long.
