While this is clearly an empirical Q that could be easily studied, in my experience camping is often very noisy, with bugs and frogs singing all night. Maybe that's why it's so easy to sleep with white noise buzzing in the background. This suggests to me that silence is less important than darkness.

The whole paleo obsession with pitch black amuses me, I have been an excellent sleeper my whole life regardless of the blackness of the room, in summer I open windows as good air flow is much more important than a black dungeon. By all means make it as dark as realistically possible, turn of LED clocks, night lights etc, but pitch black is not necessarily a silver bullet. Sleeping with an aircon on always makes me feel like ass when I wake up, so never use an aircon while sleeping. I can sleep in a room that is up to 34°C as long as I have a electric fan blowing air over me, so the white noise of a humming fan is no problem at all.

The single biggest factor that almost everyone overlooks in the obsession with pitch black - is to sleep alone. No one wants to hear that, but sharing your bed purely from a sleeping point of view is possibly the most counter productive activity that gets in the way of sleep. People go to extreme lengths to make their room pitch black and then share it with a gremlin

Rolling, tossing turning, toilet trips, snoring - how many sleeping partners have lost years of their lives because of disruptive partners?, yet in the Paleo scene you hardly ever see it mentioned , its all: Read "lights out" and black black black. Sleeping alone makes spontaneous sex an issue, which is one reason why people don't want to consider it, it definitely needs more planning and forethought to go before the foreplay.

Undisturbed sleep is paramount - how Ancestral it is, is another question, but in the modern world I consider it vital.

I cant wake up in total darkness, its confusing for my body, its like waking up with a small hangover.

My ex could not sleep because the MOON was shining into the room. The MOON. He said it had something to do with our ancestors, but sorry, the moon existed in the Paleolithic too. I think the most Paleo sleep is the way I sleep. I can sleep anywhere, anytime, with any amount of light, with a rock concert outside my window, and with men who snore. Interestingly, I started being about to sleep this way after I started paleo, before that I was kind of neurotic. Either way, I can understand that the wavelengths of electrical lights can be uniquely disruptive, so I do block those out. But our ancestors slept in environments that were often very noisy...the walls of huts are thin and you would likely hear babies, people in nearby huts having sex, crazy animals, and people talking by the fire (someone needs to keep watch).

I personally sleep fine with white noise. I live in a city so I get plenty of it. I imagine grok would have been well adjusted to the sounds of nature which any camper can tell you, are not always soft and low. I vote dark room Is a lot more important.

White noise is great, it keeps me from hearing isolated noises which tend to wake me up. I sleep much better with a fan or something on in my room.

I read somewhere (can't remember where) that modern hunter-gatherers tend to sleep off and on throughout the night, and the people who are awake at any given time tend to talk to each other. It doesn't wake the people who are asleep.

I often fall asleep with an audio book playing. It doesn't seem to negatively affect my sleep.

Our hormones respond to light and dark environments. I know of no evidence that they're also affected by quiet or by low-level, steady noise.

(I have not read Lights Out, by T.S. Wiley. There may be good information on the subject there.)

For me quiet is way more important than total darkness. I live in a noisy big city and have a huge window in my bedroom. It is impossible to make it pitch black dark so I tried wearing a sleep mask. I found despised the total darkness. I need light cues to get up or I feel groggy and awful in the morning. We are not mushrooms and I don't believe that we evolved to sleep in total darkness. Stars and the moonlight can be extremely bright. I'm sticking with my plain ol' Venetian blinds which make the room very dim but not pitch black. As for sound - I heard an interesting interview with a neurologist who stated that even when one is asleep, the brain is constantly active and reactive to noise. He claimed that even if a street siren or cars honking don't actually wake a person up -- they do disrupt restorative sleep. He claimed that this is why people who have no trouble falling and staying asleep can wake up groggy and get odd symptoms like dizziness -- big symptom of lack of restorative sleep. To test this theory, I tried earplugs to block out the big city street noise and the difference in how I feel in the mornings is like day and night -- couldn't resist the pun. Now I use the earplugs nightly because I truly wake up with much more energy. Maybe some people are more sensitive to light at night. YMMV.

I'll usually do a white noise machine, a fan in the summertime, ear plugs, and I'll adjust the dog so he's less likely to start snoring. I wish I could just "snap out of it" and be like one of those guys who falls asleep on a noisy bus, but it'll never be the case. Luckily, I've found that I require a lot less sleep these days, though I always try to shoot for as much as possible.

I totally agree that background noise is fine when you are sleeping but lack of darkness is not. As long as it is a sort of steady tone I find I get very comfortable with noise such as the drone of a refrigerated semi parked alongside at a rest stop when we are travelling, or a steady rainfall pounding on the metal roof at our cabin. However if the princess gets one little bit of light in her eyes, the ability to sleep restfully flies out the window and the split shift sleep thing happens.

Personally, I sleep fine with white noise, but any other kind of noise disrupts my sleep. If the TV is on or something like that then I don't sleep well at all. I also find that I do best if I stay in a habit of waking up at dawn. It doesn't have to be extremely dark, I just need to stay in synch with the natural cycles of light and dark outside.

how people in midsummer can have sleeped healthy?

Forest. Trees. Forest...

Get sufficient sleep (typically = wake without use of alarm clock, wake-up call, rooster crowing, etc.)

Make that sleep of good quality (how do you feel on waking and during the day?).

If that means sleeping alone in total darkness at 62 degrees F, go for it.

If you need to sleep on a waterbed under the moon surrounded by multiple $5000/night escorts just waiting to service you if you wake, by all means.

Obviously there is going to be a lot of individual variation here. Extroverts predictably (should) tolerate/endure noise activity/light better than introverts. Those whose ancestors came from cold places will probably prefer colder temperatures while sleeping as they do while not sleeping. And so on.