PhotoperiodEffect.com

18. Do I really have to keep it so darn dark at night – seems to me I've seen studies saying melatonin keeps going even under a little dim white light.

First, individuals vary. The most recent studies, looking at larger numbers of people, showed that some of us are much more sensitive than most people, and our night-time melatonin production starts to shut down when exposed to much less light than previous studies suggested. If you're experiencing any health or mood problems, it's not a bad guess that you're actually one of the more sensitive ones, and in any case, doesn't it make sense to play it safe and give yourself the best chance of experiencing some real benefits, if you're going to go to the trouble of trying to experience more natural nights?

Second, research scientists working in industrialized countries can't test what the night-time responses to light of a “normal” body used to the twelve hours of true darkness a night we're supposed to get, because there now are no such individuals. So it may be that the vast majority of the individuals they've tested have over decades partly adapted not only to fewer hours of darkness, but more lit up ones as well: they may be getting less melatonin at night than they should but be a slightly innured to light at night as well – we just don't know.

Third, the sort of research you're talking about looked at our central clock, controlled by the brain (the SCN in the hypothalamus) and not our peripheral clocks, all over our body, which we don't know a great deal about yet. Moreover, they were only looking at one measure of our response to the dark, albeit a very important one, namely melatonin levels. This may not be the whole story of why darkness is so good for us. Again, we just don't know.

Fourth, it's easy to overshoot the mark here. Chances are you don't have the technological equipment to measure minute amounts of light precisely, and even if you did; we aren't yet sure that concentrated sources of nonetheless dim light, say a small flashlight, don't trigger a response of some kind locally in the retina which could cause your brain to decide it's still day. Get it close to your eye accidentally, and it will. That is to say, approaching such a source of “dim” light multiplies it's perceived intensity many fold, in which case it may be a lot closer to daylight than you think, maybe even more intense than daylight on the retina. Perhaps one day you'll be able to buy a night light that's safe to leave on all night with a red-shifted but mixed light similar to that of stars in the night sky, and which is guaranteed to be no brighter than a cloudless, moonless night (but remember, in nature the moon isn't always out, or full, and the sky isn't always clear.) Perhaps it will consist of a single LED at the bottom of a broad cone, which only bounces light off your ceiling, so that you can never look at it directly. And perhaps there will be good research by then to reassure you that that much light at night is perfectly safe for everyone, with no consequences. But our understanding of our bodies reactions to very low levels of light at night is very new and pretty slim. It's not worth taking a lot of chances.

Fifth, human beings and their progenitors have lived inside caves, tents, teepees, and huts for a very long time now. It's possible that at least some of us may well have adapted to night-time light levels that were usually much darker even than the night sky. Especially those of Northern European ancestry who not only have had solid dwellings for a long while, but also have obviously adapted in other ways (for example by having very white skin that need less sunshine to start making Vitamin D) to very low levels of levels light even during the daytime; given the high amount of cloud cover there is in Northern parts of Europe during winter, lower sun angle, and the dense, light blocking clothing that's always been necessary (for humans as opposed to Neanderthals) to survive there.

If all these reasons seem just too cautious – don't be too sure we even know the basics. Huge surprises keep popping up in this field (chronobiology), such as the very basic fact that we actually have three kinds of sensors in our eyes, rods, cones, and ipRGCs. As is mentioned elsewhere, we only discovered that five years ago. There may be, not one or two, but many surprising discoveries still in store for us, so why not err on the side of caution? Not doing so is what got us into this mess, after all.

Certainly, I'll concede that it's possible – at least in your own individual case – that you may be right. No doubt time, and a lot more extensive studies, will tell. In the meantime, safety first. It would be a shame to go to considerable trouble to give yourself more darkness at night and a natural hormonal cycle, etc., and then get little or no effect because you very nearly created natural conditions for yourself – but not quite. This is why I personally am not using even a red LED light in the middle of the night, ever. I just use such light for fifteen minutes or less after I turn the lights completely off, and for about the same amount of time before I start turning (whiter) lights on gradually, and slowly opening blackout curtains, in the morning.