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.

Update (October 20, 2021)

I found a great example, also in Potsdam. Check out the lights at the front steps of the Ernst von Bermann Clinikum (hospital):

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

The photo doesn't do it justice. It's a beautiful installation, there is absolutely no glare, it's not too bright, the color is warm, and in real life the area between the stairs is also sufficiently illuminated by light from the surroundings. I hope I get a chance to return to these two locations with a luxmeter and a DSLR camera sometime soon to do a more proper comparison.


  1. This kind of awful public lighting seems to be a growing problem everywhere.

  2. I dont fully understand the last Block about full moon and Not needing anything more than fairly light concrete.

    Do you mean the lamps in the handrails are as bright as full moon and their direction is strictly downward?

    I cant emagine a staircase without any lamps.

    There isnt always a full moon and there are People who are Hard of sight.

    So I beg your pardon for asking this question.

    I do understand there is the need of protecting our nights animals and that too much Light has Its Problems for them.

    So I ll look forward for your answer.

    Have a great evening.

    Greetings from Augsburg, Bavaria, Eva

    1. Hi Eva,

      In the photo below, there is still way too much contrast in the scene: the brightest part of the stairway is far too much brighter than the darkest part of the stairway. If they had used less light, you would still see the stairs while being able to also see the surroundings.

      The light from the lamps in the handrails is many times brighter than a full moon (at a guess, probably at least 100 times brighter), and this makes everything around them look "dark" for everyone (including those with visual disabilities).