Lighting strategies in England

A number of English councils are experimenting with replacing dusk-till-dawn lighting with a different lighting regime, either involving dimming of lamps, or else switching them off. The Campaign to Protect Rural England has done a survey of councils to try to understand how widespread this practice is, what the councils reasons are, and to learn more about what types of strategies are being used. They've produced a 32 page report summarizing their findings that you can download for free. They've also made the short slideshow below to present the main findings:

Lighting survey results from cpre

If you found that interesting, you may also be interested in a related report submitted to the Department for Environment, Food, and Rural Affairs: A review of local authority road lighting initiatives aimed at reducing costs, carbon emissions and light pollution.

Finally, my group recently published a paper discussing recommendations that we suggest policymakers should adopt in order to reduce energy consumption, and reducing light levels during periods of little activity was one of our recommendations. The paper is unfortunately not open access, but you can download an author's copy from my personal website, Redefining efficiency for outdoor lighting.

A step by step guide to using the Loss of the Night app

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Note: This guide is for an outdated version of the app (v1.0.2). Here are the new directions for Android and iOS.

Looking for stars in Berlin

Last week we hosted the first ever international conference on artificial light at night, ALAN 2013! After two evening events of the conference, I took advantage of being out on a night with clear skies to use the Loss of the Night app in three places. I've labelled their approximate locations on this map of Berlin at Night from the Suomi-NPP VIIRS image:

The first location, "Dahlem" is in a suburb at the edge of Berlin. The second, "Spreebogen" is an unlit park across the river from the brightly lit main train station. The third was a block away from Friedrichstraße, which is the brightest place in the center of the city (at least according to VIIRS). The results of the three measurements are shown below:

The plots are similar to the ones I showed in an earlier blog post. The vertical axis shows how bright or faint the stars are. Stars I said I couldn't see are shown in red, stars I wasn't sure about are shown in blue, and stars that I said I could see are shown in black. The horizontal axis shows the time since the measurements were started (each small tick is one minute).

The horizontal lines show the estimate (maximum likelihood fit) of how bright the sky was at each location. With a few assumptions, it's possible to turn this value into a very rough estimate of how many stars you can see. In Dahlem, about 300 stars could be seen with that level of skyglow, in Spreebogenpark about 200, and near Friedrichstraße around 100. By comparing the three datasets you can see that the app is really working, and that in each location my results are quite self-consistent. Unfortunately, I didn't happen to have an SQM with me to check how closely these results compared to the actual sky radiance.

I am continuing to learn a lot about the stars and constellations by using the app!  Since September I now know learned the stars Vega and Deneb and the constellation Cygnus (the swan) very well.  I am also slowly getting used to Perseus. I think that all of the stars I wasn't sure about were in the (very sparse) constellation Draco.

Which stars are people observing?

The Loss of the Night app works by having people report whether they can see stars or not - but which stars are they looking for? Here are all of the stars that had been searched for up to August 22:

The big dipper and cassiopia are big and colored red, to help your orientation (it's an equal area projection, so it looks kind of weird compared to what you see in the sky). The plot is not filled in evenly, because the app has only been around since April (more about this in a moment).

Our app only asks users to look for the 1601 bright stars that were already part of Google's Sky Map app. But it doesn't ask people to look for each star with the same probability. It always starts with a bright star, and the subsequent selected stars depend on what you can see. Because there are so many more faint stars, some stars are searched for much more frequently than others. Here's a plot showing how often each of the stars has been searched for:

Black dots are 1-4 times, red 5-19 times, blue 20-100 times, and purple over 100 times. The most commonly searched for stars so far are Arcturus (602 times), Altair (327), Vega (322), Alioth (260), and Dubhe (184). The most commonly searched for stars are all in the upper half of the image above, because most of the app users live in the Northern Hemisphere.

You might also have noticed the big gap of missing stars on the right. That's there because the stars in the sky change throughout the year, as the night side of Earth points in a different direction as the Earth orbits the Sun. Each month when the moon goes down, users will be confronted with a new set of stars, in new positions, and with new magnitudes (brightnesses).

Here are the stars that were searched for at least once during April/May:

And during June: 

During July:

And up until August 22:

You can see that the searched for stars are marching slowly but surely "left", as the year advances. Very soon, Orion will be a risin', and hopefully many users will tell us whether or not they can still see his stars a blazin' from the middle of Central Park!

Our partners from Cosalux who programmed the app have produced a short video showing where the app had been used (up to early August), check it out:

We're tremendously happy that it's been used on all of the (inhabited) continents, and we hope that we can continue to make inroads in areas with rapid development. Sometime this fall we hope to release a new version with extended language support, including Chinese, French, Japanese, Spanish, Catalan, Polish, Romanian, Italian, and Czech. As I've mentioned before, we're looking for translators for Russian and Arabic, but we would need the translation done in the next days. If you could do the translation, or know someone who might be able to, please send me an email!

[Note: updated with higher resolution version of the video on Aug 31, because blogger reduced the resolution.]

Why more stars=better observation

Every observation produces useful data, but the more stars you observe, the more precise your data will be. To demonstrate this, here is an example of a minimal complete observation (7 stars), taken by my former colleague Marco Starace near the center of Dresden, Germany last night:

The black stars show stars Marco could see, and the red circle is the one star that Marco was not able to see (Fainter stars have a larger magnitude). Based on this data alone, our best guess for the limiting magnitude (faintest visible star in the sky) is probably somewhere around 4.7. But we would also have to assign a very large uncertainty to the observation, because it's possible that Marco made a mistake with star 6 or 7 (or even on other stars). If he made a mistake on the last star, the limiting magnitude could be as large as 6.5, and if he made a mistake on the 6th star, it could be as low as 3.8. It is critically important to understand exactly how large this uncertainty is, so I hope that we will be able to obtain a grant to study this in the future.

But look what happens when Marco continued past 7 stars (the blue square is a star he was unsure about):

Now we have a lot more information. Our estimate for the limiting magnitude will now be lower (near 4), and the degree of uncertainty will be far smaller. It now looks quite likely that the limiting magnitude is smaller than 4.4, and nearly certain that the limiting magnitude is above 3.

Whenever you observe more than 7 stars, you help us in two ways. First, your observation will be of a higher quality, because of the reduced uncertainty. Second, you help us to better understand the results of observers that search for only 7 stars. That's because we can make an estimate of limiting magnitude based on your first 7 stars, and then test how well that estimate holds based on your additional stars. This will help us to eventually produce unbiased estimates, and it will also help us estimate the uncertainty on those 7 star observations.

One other thing that I hope this data conveys is that incorrect decisions aren't the end of the world. If you search for a lot of stars, then we will be able to make sense of your data, even if there are occasional mistakes somewhere. With time, we will learn which stars users find it easy to make accurate decisions about quickly, and we will also learn which stars are problematic (long decision time and high percentage of incorrect decisions). This information will make future versions of the app more accurate and also easier to use.

So thanks to Marco for his observations, and thanks to all of you who go past seven stars!

(For anyone just joining us, you can download the Loss of the Night app here. Also, we need a translator for the Russian and Arabic version ASAP! If you're interested, please contact me.)