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.

Wednesday, March 8, 2017

Tweetstorm about light pollution and citizen science

Thursday, February 23, 2017

A step by step guide to using the Loss of the Night app on Android (v2.1.7)

This is a step by step guide to using the Loss of the Night app for Android (v2.1.7). If anything is unclear, let me know in the comments and I will revise the instructions.
Instructions for iOS
Infos auf Deutsch


Android phone running at least Android 2.1, but preferably Android 4 or higher.
The phone must have a compass and GPS.
A location with a light polluted sky.
A friend to accompany you while you are doing observations.
The ability to see at both near and far distances without removing glasses.
Your phone case must not have a magnetic clasp.

Before you start:

The Loss of the Night app is meant to be used outside at night. For safety's sake, inspect the area where you plan to do your observation during the day, and make sure that it has level ground where you can move around safety.

People using mobile phones are less aware of their surroundings, so you should never use the app alone outdoors at night! Always take a friend to watch out for potential hazards while you are using the app. These could include tripping hazards, vehicles, dangerous weather, and crime. If for some reason it's not safe to do an observation, turn off the app and leave the area immediately!

Installing the app:

To install the app, do a search in the play store for "Loss of the Night". Alternatively, type this address in your browser:

or go to the page by scanning this QR code

Running the app:

When you first open the app it will display the privacy policies and terms and conditions. To go further, you will need to read the conditions and then click "accept" at the bottom right hand of your screen.

When you click "accept" you are brought to a screen with information about light pollution. Click "next" to go on.

Next comes a screen titled "USE". We would appreciate it if you would register and tell us something about your vision and your observing experience. Click "Register Now" or just "Continue as a guest".

If you choose to register, you will be asked to indicate your approximate age (use the up and down arrows to change), and you can click the buttons to tell us whether you wear glasses and how much stargazing experience you have. We also ask you to provide a username and your email. If you provide your email, we will send you a thank you email within about a month of your observation. In extremely rare cases we contact a user if we have questions about their data. Click "save" when you have entered your data.

Making an observation

After you save your data, you'll come to the main menu. To make an observation, click "start observing stars". At this point, the app will only work properly if you're outside, as it needs to get a GPS signal. This can sometimes take up to a few minutes. If it takes longer than that, try using an app like "GPS Status" to check if your phone's GPS is working. Some phones have a problem that prevents the app from getting your position from GPS. In this case, try putting your phone in airplane mode and starting the app again. We are working to understand and fix the problem, but this provides a temporary fix for some Android devices.

If it is still twilight or if the moon is in the sky, the app will give you a message that it's not "dark enough". The moon prevents measurements from being made for about two weeks at a time, so if this is the case, the app allows you to add a note to your calendar when the next observing period at your location starts. (Click "Measure anyway" if you'd like to test out the app.)

(At this point, in locations with a lot of magnetic material or electric cables around, your phone may give you a warning that your compass has a problem. You can try to calibrate it by moving your phone in a figure 8, or turning it around all three axes. It this doesn't work, then there is either a problem with your location or your phone's compass. You can opt to measure anyway, but the stars displayed on the phone will likely be shifted compared to the ones in the sky.)

Next, you are asked to input the current weather conditions. Click the relevant symbol (or symbols), and then "Continue".

Star search

The app will now try to direct you to one of the brightest stars in the sky. Turn your body in a circle and watch how the arrow changes direction. Tilt your arm down so that your app is pointed toward the ground, and it will show you the stars that are under the Earth. Tilt your arm up to the sky, and it should show you the stars that are currently in the sky. It is very important that while looking at the stars in the sky you keep the phone's screen oriented perpendicular to your body!

Now search for the star the app is asking you to look for. Turn your body until the arrow points straight up, and then raise your arm until you see a star with a flashing crosshair on it. When you find the star, the circle will expand to fill most of the screen and three buttons will appear at the bottom of the screen.

Your job is to decide whether the star the app pointed you to is visible to your naked eye or not. If you can see the star, then click "Star is visible" on the bottom right. The app will then ask if it's "clearly visible" (very obvious and easy to see), "barely visible" (you can see it while looking at it directly, but just barely), or "visible only with averted vision" (you can see the star only when you don't look directly at it).

If you cannot see the very first star, there may be something wrong with your phone. The app always starts with one of the very brightest stars in the sky, which should be visible even inside of large cities. The most likely problem is that your compass is not working properly. If your phone is in a carrying case that has a magnetic clasp, you will need to take the phone out of its case and then recalibrate the compass (quit the app, and then start it again).

If the stars appear to be bouncing around a lot, you may be in a location with strong electromagnetic fields (e.g. near overhead or buried power lines). It's best to try to use the app in a grassy area, like a park. On some Android devices, quitting the app and then starting a star search again results in a smoother response. Finally, it's possible that the compass or GPS from your phone is not working properly, and if this is the case the app will not work on your phone.

Continuing your observation

Each time you find a star, the app will ask you if it's visible or not. If you can't see the star for some reason, click on "Not visible or unsure". You will then be brought to a menu that gives you four options for why you can't see the star. Choose the option that is most appropriate:

If you're not sure which star we're asking for, or if for some reason you find it too hard to tell whether the star is there or not, choose "I'm not sure if it's there or not".

Once you have made a decision on a total of 8 stars, the app will pop up a message that says "8 stars reached". You will have the option to quit, "Register" (if you haven't done so already), or "3 more stars". We would really appreciate it when you observe a few additional stars, because observing more stars improves the accuracy of your measurement.

If you click "3 more stars" the app will ask you again when you reach 11, 14, and 17 stars. After that, if you want to continue, it won't interrupt you anymore, and you can click the "back" button whenever you are ready to end your observation. When you end your observation, the data is automatically sent to a server hosted by the GLOBE at Night project if your phone has an Internet connection. If you have a data plan, this should happen immediately, otherwise, it will be transferred the next time you have a WiFi connection.

When you finish your measurement, the app will let you know how faint the faintest visible star in your sky is (naked eye limiting magnitude), and approximately how many stars are visible in your sky. For reference, in places without light pollution, it's possible to see many thousands of stars. The app will also let you know how consistent your measurements were. The more you use the app, the better you will get at making accurate, consistent observations!

Accessing your data

You can view all data collected by participants via the My Sky at Night website. Click the blue bar at upper right to select which years and data sources you would like to observe. An overview of the My Sky at Night website is available here.

The app also stores the results of your observations directly on your phone. In the main menu, click on "User data" and then "My measurements". A screen will come up showing the dates that you did observations, and the results. If you click on an observation, then the app will show you the names and magnitudes of the stars that you looked for. (Stars with smaller magnitudes are brighter.)

Personal settings

The "User data" menu allows you to change some of the app settings. You can toggle the display of star and constellation names, and choose whether some screens display on start up. You can also increase the size of stars and fonts (this might help if you are farsighted). If you find that the screen is too bright during your star observations, click "Make screen darker" and see if it helps.

Additional information:

As the year goes on, different stars appear in the night sky over your head. If you enjoy using the app, feel free to use it as often as you like!

The app contains a lot of information about light pollution that you might find interesting. You can access this information by clicking on "Project information" in the main menu.

You can also switch between "Day mode" and "Night mode" in the main menu. Please use the Night mode when making observations, because it is designed to have less of an effect on your night vision.

If you have a Sky Quality Meter, you can submit data taken with the device as well. From the main menu, click "Submit data from SQM" and then use the scroll wheels to enter the SQM value.

More information about the Loss of the Night app project is available on our blog.

If you'd like to read a paper that demonstrates the scientific value of citizen observations of naked eye star visibility, you can access it for free here.

The app is available in 15 languages, and automatically uses the language that your device is set to.

Thank you!

Thank you for taking part in this project! Your data will help us understand how the brightness of the night sky is changing around the world. Because we are interested in understanding long-term changes, the most valuable data are observations taken at the same place year after year.

Friday, February 10, 2017

Excellent LED streetlamps

This December I visited my family in the town of Wetaskiwin, Alberta, Canada. The first evening that I drove into town I immediately noticed that the city had switched from Sodium lamps to LED, and I was very pleasantly surprised to see that the LEDs they chose shine the light very carefully. To see what I mean, take a look at the photo below:

Good streetlamps are invisible by Christopher Kyba is licensed
under a Creative Commons Attribution 4.0 International License.

You almost can't see the streetlights at all, because they shine light on the street, rather than into your eyes. On most lit streets around the world, you can see the lamps from kilometers away, because they shine a portion of their light directly into drivers eyes. These photos from Wetaskiwin show how unnecessary that glare is.

That being said, the lamps aren't entirely glare free, particularly for pedestrians (see below). However, in terms of (white) LED streetlamps deployed in an urban setting, these are the best I have yet seen.

Close-up glare by Christopher Kyba is licensed under
a Creative Commons Attribution 4.0 International License.

When you have a good light distribution, then you can light the streets and sidewalks, and avoid shining light into peoples bedroom or living room windows. Take a look at the photo below. One house is lit with Christmas lights, but did you notice the one to the left? The street and sidewalk for that house are lit, but the facade of the house is not.

Orion over LEDs by Christopher Kyba is licensed under a Creative Commons Attribution 4.0 International License.

Camera photos don't accurately represent what our eyes really see (which is why I often show photos using two different exposures). I didn't do that (or HDR) in this case, because I hadn't planned on taking photos and wasn't dressed for the cold. But you can take my word on it: as a pedestrian, you have no problem to see the house on the left, the camera doesn't show it because the exposure was set to highlight the lit snow.

Thanks to Rod Mc Connell and Noel Smith, I was able to get some information about the lamps themselves. They are the "RoadFocus" series manufactured by Philips lighting.

The only negative side with the current lamps is that they are 4000 Kelvin, which produces considerably more skyglow than a lamp with a lower color temperature (warmer, less blue light). But I hear the city is planning on switching to 3000K in the future, and is also thinking about reducing the wattage so that the lights don't shine overly brightly.

So hats off to the city of Wetaskiwin for choosing driver friendly low-glare lights!

Here is a copy of the original photo, in case you'd prefer it without the text.

Good streetlamps are invisible by Christopher Kyba is licensed
under a Creative Commons Attribution 4.0 International License.

Monday, January 30, 2017

I use my sun visor at night...

A loss of the night app user from Trier, Germany, recently passed me a few photos to share with you. They show the results of a recent lighting "upgrade" in his area. The problem with the new white LEDs is that they are extremely glaring. The glare is in fact so bad, that he needs to drive with the sun visor down! Glaring lighting makes it harder for drivers to see pedestrians, but there are efficient LED streetlamps for sale that aren't as glaring. So if your city installs something like this, be sure to complain! Even better, let the city council know you care about quality lighting before they make a change!

This work is licensed under a
Creative Commons Attribution 4.0 International License.

This work is licensed under a
Creative Commons Attribution 4.0 International License.

This work is licensed under a
Creative Commons Attribution 4.0 International License.

This work is licensed under a
Creative Commons Attribution 4.0 International License.

This work is licensed under a
Creative Commons Attribution 4.0 International License.

He also sent me a photo of the skyglow on the horizon towards the Big Dipper:

This work is licensed under a
Creative Commons Attribution 4.0 International License.

(The title of the blog post comes from a song by Canadian singer Cory Hart: Sunglasses at Night. If you've never heard it, take a listen and see if it reminds you of another famous song)

Thursday, January 12, 2017

Converting World Atlas floating point values into sky brightness predictions

Updated January 9, 2020.

Over the past several years, I was involved in the team that published the "The new world atlas of artificial night sky brightness" last summer. My main role in the project was in calibrating the map based on sky brightness observations. The two main sources of observations were the all-sky brightness surveys of the US National Parks Service Natural Sounds and Night Skies Division and observations with hand-held or vehicle mounted Sky Quality Meters (SQMs). In the end, we chose to do the main calibration with the SQM dataset, because thanks to the participation of citizen scientists, it covered locations on all 6 inhabited continents, including many more urban locations than were otherwise available. The NPS surveys, some additional telescopic data, and data from permanently mounted SQMs were then used to verify the result from the SQMs.

Now that the Atlas is published, many researchers are interested in using the map to understand their area. For most people, and also for many researchers, the colorized version of the map that we've made freely available is sufficient. For example, if you're looking for a good place to go stargazing, you'll do fine with the colored map. You can either view the Atlas with from within your web browser, or you can  download a set of tiles for Google Earth.

The rest of this post is technical, and will only interest a small subset of blog readers.

Some researchers will want to use the floating point dataset for further analyses*. The data is now openly available, and can be requested via a form from this page. The form sends an email to Fabio Falchi and Christopher Kyba, so that we are aware of who is using the data and can follow up if necessary.

The floating point data are stored in a single GeoTIFF file covering nearly the entire world's extent (arctic latitudes excluded). The map reports simulated artificial zenith luminance in mcd/m2. If you want to use the data to estimate how bright a real sky is, you need to add in the natural portion manually. Natural light at night is quite variable, mainly due to the position of the Milky Way and the amount of airglow that is present.

When we calibrated the World Atlas, Dan Duriscoe from the US NPS provided me with estimates of the natural sky brightness for the specific date and time the observations were taken at each of the tens of thousands of locations worldwide. These observations were taken from 2007-2015, with the largest number of observations taken in 2013 and 2012. Over this time period, the predictions for the natural sky brightness ranged from 21.01 to 22.11 mag/arcsec2. The most typical value was 21.65 mag/arcsec2 (or about 0.236 mcd/m2). The average value changed over the years (due to changing solar activity), from faintest values of 21.88 mag/arcsec2 in 2007 to brightest values of 21.58 mag/arcsec2 in 2014.

Once you choose a natural sky brightness**, you should add that value (in mcd/m2) to the artificial sky brightness from the Atlas. Let's call this value "X". To convert this value into a prediction of what an SQM would see, use this equation:

SQM_pred = -2.5 log10(X/ (10.8 x 107))

I'd like to thank to Salvador Bará for sending me a question that prompted me to write this blog post.

* For researchers using the data in publications, please note that the data DOI is separate from the World Atlas publication. If you write a manuscript using the data, you should separately cite both the World Atlas publication and the data DOI.

** Note that in the model we also included an additional free parameter "S", which is a linear scaling factor for the natural sky component. We put it in to account for the fact that the SQM band does not match the V band. The best fit for this value was 1.15, meaning that the average natural sky brightness was increased from 21.65 mag/arcsec2 (0.236 mcd/m2) to 21.50 mag_SQM/arcsec2 (0.271 mcd/m2).