Recently I’ve been reading an interesting book by Paul Bogard, The End of Night. It’s non-fiction, and is based around the increasing amounts of night-time light in the developed world—and why that may not be a great thing.
Just 200 years ago, before electric lights, the night sky—complete with the swath of the Milky Way, and other naked-eye observable galaxies—was spectacular on any clear night from anywhere on Earth. Today, however, few in the developed world see that a few times a year, let alone on every clear night. Instead, our nights look like they do in the photo of Berkeley above, with a milky haze of yellow-orange light from the 589 nm sodium D lines (admittedly there is some fog in the picture too).
There were four key messages I took from the book.
First, straightforwardly, is that a dark night sky is incredibly beautiful, and we should preserve that beauty. Seeing the Milky Way clearly with the naked eye can be a powerful experience especially for those who have rarely or never have. Unfortunately, very few places in western Europe (or the eastern half of the US, or populated areas in the western US) are near dark skies. Bogard cites a statistic that 80% of children born in the US today will never see a truly dark sky. In my experience as a teaching assistant at Berkeley going on a geology field trip to Bishop, CA and the eastern Sierras, I can attest to a large proportion of the students being quite surprised by all the stars visible from such dark skies.
Adding light doesn’t make it easier to see. Sure it makes it easier to see initially when you first go from the light into the dark, but if the light isn’t in the right places, it actually makes it harder to see. I have biked at night on roads where the streetlights made it very difficult for me to see the road, because the lights were so bright and everything else so dark. Glare from bad lighting makes the lighting less effective. It’s also light going places it isn’t needed or wanted, which is wasted energy (and money, and CO2 where electricity comes from fossil fuels). The picture at top has a number of lights shining directly into the camera, miles away; all that light is wasted and unneeded. Bedrooms have light streaming in from outside even at night, which causes its own problems.
People are evolutionarily adapted to sleep at night, and our bodies expect for it to be dark at that time. Longer periods of light are decreasing the amount and quality of sleep we get (particularly night-shift workers), and those have significant detrimental public health consequences including increased risk of cancer.[1 and references therein] Turning off or dimming the lights at night—especially blue light and light in the bedroom—could help us sleep better and be healthier for it. Minimizing the number of people who are working at all hours of the night and thus exposed to the health risks of doing so would also be good, both from a moral and economic perspective.
Finally, it was made clear throughout that the point here isn’t to turn off all the lights and go back to the stone age, but rather to be thoughtful and deliberate about our outdoor lighting. Making light fixtures which put light where it should go (i.e. down on the ground, not out to the sides or up) and using them only when needed is fairly simple. How much light is really needed at a car dealership, ice rink, or empty parking lot in the middle of the night? Gas stations are often extremely brightly lit, yet most of that light isn’t needed to pump gas or wash the bugs off the windshield. In fact, pulling out of a bright gas station at night can be dangerous since your eyes will have adjusted to the brighter environment and it will take a few minutes for them to dilate again and bring your vision back to its optimum level.
Supposing I turn off my 60 W worth of porch lights (sadly not the dark-sky friendly type) for an average of 10 hours/day year round (3650 h), that reduces my electricity consumption by 219 kWh (780 MJ). At a residential electric rate of $0.08/kWh, that translates to a savings of $17.52 annually, as well as a CO2 savings of 150 kg (3400 moles). It also makes my bedroom darker.
I went outside one night recently when it was clear (albeit humid). I have an urban view, and can only see ~25% of the sky. From my deck, I counted twenty stars. That’s right, I could only see 20 stars. Extrapolating for the full-sky view gets me up to 80, and if we want to be generous we could round that to 100. Compare that to the dark(ish) sky pictured above, and you can see that there’s really a huge difference. In this neighborhood, too, there’s enough stray light running around (even in the summer when leaves block it) that turning off my outside lights isn’t making it hard to get around.
Night can be a pretty neat time. In college, I would occasionally go cross-country skiing at night. Sure, I would have a headlamp with me, but on a clear night I typically didn’t use it. Even cloudy nights, thanks to some local light pollution, were easy to ski without the aid of the headlamp. Being outside at night in the crisp, quiet solitude of a snowy winter was amazing. It’s part of what I missed while in graduate school in a bright, noisy city where it never snows.
After reading this book, I’m looking forward to the Heard Island expedition even more, because the southern ocean, like Antarctica, is home to pristine skies free from artificial lights. Of course, unlike Antarctica, the likely sky condition is mostly cloudy or cloudy, so getting a clear night may be very rare. That will only serve to make the moment more special, if and when it happens. I will bring a camera, and I will try to get a picture of such an event. But that picture will be but a still, lifeless version of the magic at Heard Island.
 Hansen, J. J Natl Cancer Inst (2001) 93, p. 1513–1515. DOI: 10.1093/jnci/93.20.1513