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.