Monday, December 4, 2017

Light trespass

In previous "view from your app" images we have only had a few examples of light trespass: when light illuminates something it is not meant to illuminate.

My colleague Catalin-Daniel Galatanu sent me an excellent example of light trespass from Iași, Romania. In the photo below, you can see a residential building that is brightly illuminated by the spill light from church facade lighting:

Light trespass by Catalin-Daniel Galatanu is licensed under
a Creative Commons Attribution 4.0 International License.

Catalin used his images to calculate the luminance of the facades, and got the following result:

Light trespass luminance by Catalin-Daniel Galatanu is licensed under
a Creative Commons Attribution 4.0 International License.

The lit areas have a luminance of 2-4 cd/m2. To calculate the illuminance on the windows it would be necessary to know the albedo of the building, but with a rough guess of 0.7 that would imply around 15 lux. I think it would be pretty unpleasant to have such a bright light shining into either your bedroom or living room! Catalin points out that in addition to the light in the room, the people living here have lost not only the view of the stars from their window, but they wouldn't be able to enjoy their view over the city at night, due to the unpleasant glare.

It's important to stress that there's absolutely no reason that it has to be this way. With more carefully directed lighting, the church could be illuminated with limited or no spill light. Furthermore, it's not necessary to shine so much light on a facade for it to have the impression of being illuminated. I hope to soon be able to share a great example of how churches can be more effectively lit (paper in review).

Monday, October 16, 2017

Types of light pollution

Here's a handy image for explaining some of the different aspects of light pollution.
This work is licensed under a Creative Commons
Attribution-NonCommercial 4.0 International License

The image on top right is from Andrej Mohar, the other 5 are from me.

Wednesday, July 19, 2017

When church lighting goes wrong

A blog post in tweets

Friday, July 14, 2017

Great observation from Portugal

I wanted to share a great observation made a few months ago by a Loss of the Night project participant from Portugal:

As you can see, there is a very clear separation (white line) between the stars that were visible (yellow, orange, and brown) and those that were not (black). You can also see how thanks to the observer examining so many stars, you can have a lot of confidence in the result, and can even measure how consistent the observer's result is. When you first start using the app, you might not have results as consistent as this, but with a bit of practice it becomes easier and easier to cover a lot of stars quickly.

This also demonstrates why the app is a better method for estimating limiting magnitude in bright places than star chart based methods like Globe at Night. In this case, the naked eye limiting magnitude was around 3.9 ± 0.1. The star charts of Globe at Night only allow you to choose between integer limiting magnitudes, which in this case would be "about 4". In addition, with Globe at Night we can't be sure how careful a participant is, and we found that compared to skyglow models, the standard deviation of Globe at Night observations is about 1.2 magnitudes.

While the app can provide more accurate data, I want to stress that it's not a replacement for Globe at Night! The app doesn't include stars with limiting magnitudes above about 5.2, so in areas with little light pollution, Globe at Night is a better method. In addition, the Globe at Night time series goes back over 10 years, and there is therefore a lot of value in continuing to contribute to it. In my opinion, it's the best system we have for tracking global changes in skyglow. So please consider contributing to both projects!

If you make an observation with the app, you can easily see a similar plot for your own results. Just head to My Sky at Night, zoom in to the area where you made your observation, and click on it to bring up this chart.

Monday, March 27, 2017

Unnecessary light on a field

My colleague Andrej Mohar recently shared this image with me:

This work by Andrej Mohar is licensed under a
Creative Commons Attribution-NonCommercial 4.0 International License.

The photo shows the light spread from single 20W 4000K LED that was recently installed. The lamp itself is designed to have no direct upward emissions (which is good), but much of the light is shining into an area which doesn't need to be illuminated (which is very bad), and even the area that is intended to be illuminated happens to be a region of very low traffic. It is so out of character for the region it is installed in, that at least two people in the nearby village have already officially complained about it.

In these sorts of cases, it doesn't matter how efficiently the lamp converts electricity into visible light. The light itself is unnecessary, so it is an inefficient use of electrical resources.

Thursday, March 23, 2017

Milky Way and Skyglow from the Fürstein

Martin Würzer recently sent me this amazing panorama showing the skyglow over Switzerland:

Fürstein 360 Panorama v2 by Martin Würzer is available
under a CC BY-NC-SA license

He took the photo on New Year's Day 2017 around 8 pm, from the peak of the Fürstein. The light from Milan is visible at the far left. It's an amazing photo, and you can see it in full resolution by clicking on the name of the photo in the caption above.

Martin also sent me this image, which shows where at least some of that waste light is coming from:

Illuminated facade by Martin Würzer is available under a
Creative Commons Attribution 4.0 International License..

That photo was taken shortly before 3 am! There is some good news associated with this photo, however. By having a polite discussion with the architect and the firm that owns the building, Martin convinced them to remove the light that illuminates the facade, and to also improve the other lamps so that they produce less skyglow. Great job Martin!

For Swiss and other German speaking readers, Martin provided two useful references:

Friday, March 17, 2017

Spotlight on air

My colleague Martin Morgan-Taylor sent me this photo of a newly installed floodlight that doesn't actually seem to be pointed at a building facade, or really anything in particular at all.

Misdirected floodlamp by Martin Morgan-Taylor is licensed
under a Creative Commons Attribution 4.0 International License.

There are some flower beds nearby, but if they are meant to illuminate the flowers they are pointed in the wrong direction! (Incidentally, surely only someone who hates fireflies, glowworms, and other nocturnal insects would do such a thing, no?)

The design is such that the lamps will produce a lot of glare, making vision in the area worse. At the same time, about half of the light emitted is going to go up into the sky, producing skyglow.

One final, but really important point: It does not matter how "efficient" this lamp is in lumens/Watt. Almost none of the light produced by this lamp will assist humans with a visual task, so the true efficiency in the commonsense meaning of the word is near zero.