Seth's Blog

I’ve collected even more observations supporting the idea that outdoor light improves my sleep, as discussed earlier. Now I’d like to get some idea of the dose-response function. To sleep really well do I need two hours of outside light? Four hours? Eight hours?

I’ve started to rate my sleep on a scale where 50 = average sleep (average for the months before I started spending more time outside) and 100 = best sleep imaginable (which I got after standing about 10 hours). And I’ve started to use a stopwatch to measure how long I spend outdoors. I’ve also been using a light meter to measure the strength of light in various places. When I’m outdoors it’s almost always in the shade. Today I discovered that sitting indoors next to a cafe window the incident light was just as bright as when I sit outside. Great to know because indoors I can plug in my laptop.

A 1994 book chapter from Daniel Kripke‘s lab reported a correlation (0.24) between low light exposure and “abnormal sleep.” So the connection I am now studying has been plausible for many years. The measurements I am now making are easy, but no one made them. Perhaps too many people believe that anything other than a double-blind trial with control and experimental groups is, as Peter Norvig, Google’s Director of Research, believes, a “mistake.”

Today I had lunch with a friend and said, “I’d like to sit outside.” I answered my phone indoors and went outside. I answered my email sitting outside.

I’m now convinced that more outdoor light exposure makes me sleep better — better in the sense that I wake up feeling like I have slept more deeply. Whatever sleep does, it has done more of it. I’m convinced because I have gotten this well-slept feeling after six or seven days during which I spent several hours more than usual outdoor and did not get this feeling after two days when I spent an average or less-than-average amount of time outdoors.

I have slept this well before, but only after standing for 9 or 10 hours, which wasn’t easy. (Nowadays I stand about 6 hours/day.) Whereas spending more time outside is easy. I’ve ordered a sunshade for my laptop.

I am going to start to measure my sleep quality with a rating and keep track of how long I spend outdoors.

Daniel Kripke, a professor of psychiatry at UC San Diego, has done lots of research on the effect of exposure to varying amounts of natural light. His subjects often wear meters that record the illumination level. His latest paper (2004) on the connection between outside light and sleep reports several weak correlations between amount of light exposure and sleep quality:

mesor log10[lux] [a measure of light exposure] was . . . positively correlated with sleep quality (rp = 0.17, p < 0.005), and negatively correlated with reported trouble falling asleep (rp= -0.17, p < 0.005), waking up several times a night (rp= -0.18, p < 0.001), waking up earlier than planned (rp= -0.09, p < 0.10), and trouble getting back to sleep (rp = -0.11, p < 0.025).

The introduction states:

Bright light has been recommended for treatment of various sleep disorders [13], but very few experimental trials have been reported.

“Very few” seems to mean none, given the absence of citations.

The paper ends:

In conclusion, low illumination has a small relationship to . . . sleep disturbances.

Yesterday I deliberately spent almost all day indoors. I didn’t change anything else. This morning I woke up feeling less refreshed than usual. Here are the last three days:

Day 1: Try to spend lots of time outdoors (in the shade). Result: Wake up feeling more refreshed than usual.

Day 2: Try to spend lots of time outdoors (in the shade). Result: Wake up feeling more refreshed than usual.

Day 3: Try to spend as little time outdoors as possible. Result: Wake up feeling less refreshed than usual.

My belief is increasing. Via Google I found this:

Person 1: During the warm months of the year, I swim …a lot! . . . The amount I sleep during swimming season can increase by 1-2 hours.

Person 2: Your probably sleeping longer due to all the extra calories and physical exerction you use by swimming.

Person 1: Nah, it’s the same physical exertion year round for me. I exercise year round. But in the warm months, my exercise takes me outside where I am exposed to sunlight instead of artificial indoor light. That’s how I know it’s the sunlight that helps me sleep better.

I also found this:

We have found that people who are outdoors more have fewer sleep problems.

From an interesting mini-book about the dangers of sleeping pills (apparently the new ones cause cancer). I haven’t yet found the study it refers to.

In an airport a few weeks ago, chatting with a stranger, I told her about my self-experimentation. When I stand a lot, I sleep better, I said. She said that sunlight had the same effect on her: When she sunbathes, she sleeps better. Better how? I asked. More deeply, she said.

I had found that morning sunlight (an hour, say) helps me sleep. Her idea was different: No one sunbathes in the morning. She was saying that the amount of sunlight matters independent of the time of day.

This was fascinating because I remembered two days, prior to studying the effects of standing and morning light, after which I had slept very well (i.e., woken up feeling very well-rested):

1. A day when I went to many artists’ studios to look at their work (an event called Open Studios).

2. A camping trip.

Both days I was on my feet a lot. But both days I was also outside a lot, I realized.

Yesterday I gave her idea a test: I spent more time than usual outside — about three hours more, I’d guess. I spend a lot of time sitting in cafes writing; yesterday I sat outside instead of inside.

This morning I woke up feeling unusually well-rested. This bears more investigation.