Wednesday, July 1, 2020

Changes in light emissions during the COVID-19 shutdowns

At the start of the lockdown periods in Europe and North America, a few people speculated about what it might mean for changes in light emissions. I was skeptical that we would see much of anything.

Shortly afterwards, NASA showed some results for Hubei province in China:

We are still waiting for the monthly satellite data composites for February-April to come out, but I still don't expect to see much in most places. However, it turns out that there were some pretty dramatic changes in at least a few places around the world. The best example I've seen of this comes from Poland. Check out these two photos of Kraków, Poland, that Mateusz Windak posted on a Polish forum:

This work by Mateusz Windak is licensed under a Creative Commons Attribution 4.0 International License.
Click for the full size version.

Here's what Mateusz had to say about the photos:

The animation shows differences before and after midnight, when the Cracow city lights are switched off. After the switch off, only private light sources and the highway in the foreground remained. The lights were turned off for a month and a half from 00:00 to 04:00 each night due to the lack of traffic during the lockdown period of the COVID-19 pandemic. Currently, Cracow has stopped shutting down the lights, but some other cities are still continuing this practice.
The photos were taken from Wieliczka, a neighboring city, using a Mavic Air drone. They are four panel panoramas, the settings for each photograph are: 2s, ISO1600, f/2.8.

Thanks for sharing your photos Mateusz! I find it really impressive that in addition to the lights going off, you can also see the decrease in sky brightness

Friday, June 19, 2020

Panel discussion about light pollution and dark skies

A while back I was invited to be part of a panel discussion titled "Light Pollution & the Dark Sky Movement". Check it out:

[d]arc thoughts: Episode 4 | Light Pollution & the Dark Sky Movement from [d]arc media on Vimeo.

Thursday, June 11, 2020

Loss of the Night app video tutorials

A group of undergraduate students from Worcester Polytechnic Institute recently produced tutorial videos for using the Loss of the Night app. They made separate videos for the Android and iOS versions. Feel free to share them!



Big thanks to Aaron, Kai, Ryan, and Vinit for producing these videos!

Tuesday, June 9, 2020

Removing natural light from nighttime satellite images

My student Jacqueline Coesfeld recently developed an analysis that will be interesting for readers of the blog who work with satellite data. I summarized it in a series of tweets. You can click on the tweet to read the thread, or see the unrolled version here.

Tuesday, March 24, 2020

Street view with the lights out

Ken Walczak from the Adler Planetarium in Chicago recently sent me a set of two cool photos I want to share. Here's what he had to say about them:

I got home after an evening event and didn't realize at first why there was such a different quality to the ambience of our neighborhood. It took a moment to realize that due to a film shoot, the city had turned off all the lights on the main streets. I walked the dog, said "Hi" to neighbors walking down the street, just as normal and safe as a typical night. I snapped some photos. I set the exposure to try and capture the visual quality of the experience (1sec f/3.5 at ISO 800). The lights came back on later in the night and I shot with the scene with the same settings.

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

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

Animated version

In an area with significant skyglow, I have often found that you actually have the better vision in unlit areas (e.g. parks, rooftops) than on lit city streets. The reason alleys in big cities are dark is not generally because there isn't enough light for you to see, but because of either glaring lights creating more contrast than your visual system can deal with, or else because you've left a really bright street and your eyes haven't had a chance to adapt.

In case you didn't see it already, check out the other amazing photo of clouds glowing over the Chicago skyline Ken sent me a few months ago.

Wednesday, February 26, 2020

How not to light a staircase

Staircases represent a tripping hazard, and it is therefore not unreasonable to illuminate them under certain circumstances. However, as I have shown in the past, poorly designed illumination is actually much worse than no illumination at all. A (literally) brilliant example of this comes from the "Lustgarten" park in Potsdam:

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

These lights combine both the wrong direction (shining horizontally rather than downward) with being extremely bright, which makes them terribly glaring, and makes it harder, rather than easier, to safely ascend the staircase. (Right after I took this photo, I misjudged the position of the first step and stumbled slightly, even though I was trying to shield my eyes from the glare).

What could be done instead? One interesting application I have seen is LEDs installed on the underside of a handrail. Unfortunately, I don't have any photos of a really good execution of this. Here is an example of an attempt that didn't quite work out:

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

It's better than the example above, but is still a problem, because it's still too bright near the lamps. What pedestrians need is accent illumination that helps them separate the stairs from the surroundings. When you have most of the scene lit with ~0.1 lux from skyglow and other distant light sources, and you then put 50 lux directly under the handrail, you've now created a 500:1 contrast. Your visual system doesn't deal well with that level of contrast, and it makes it harder to see.

For areas that are not brightly lit, moonlight provides a good benchmark. A typical full moon night is around 0.1-0.2 lux, so if you're illuminating a fairly light concrete, you really shouldn't need any more than that.