In your presentation, ‘Tale of Four Cities’, you talk about contrast-based criteria in outdoor spaces. Would you please explain this, and why it’s different, and preferable to, uniformity criteria?
Contrast is how we perceive an object against different uniformity or brightness backgrounds. I did a contrast experiment as part of lighting training for the Navy Anti-Terrorism Team. Actually, we tried to break into buildings at night – it was terrifying! But, it was a controlled scenario, and was meant to report on security breakdowns. The highly secure buildings were concrete, with concrete sidewalks, and what color did the team wear? Black, as one would naturally assume. The squad commander and I both wore white or khaki, and no one could see the two of us against all that concrete.
We’ve found in our studies, including the ‘Tale of Four Cities’, that color has a tremendous effect on contrast, even with people who are chroma-challenged or color blind. We’re not to the point where we have definitive answers yet, but I can tell you that, for example, you can see yellow from anywhere. In fact, it caused problems in one of our experiments because people could see it in the next sequence, ten blocks away.
We also found that the more non-uniform the lighting, the faster objects were detected; we kept dimming the lights, hoping to jump off that plateau of visibility, but instead we kept skirting across the top, even down to the 25% lighting level. Our research indicated a need to change from vehicular- centric to pedestrian-centric lighting, because the darker the street in a high ambient area, the better people can be seen.
We could see so much better if we had darker streets and brighter sidewalks. I’m also a firm believer that we should look at semi-cylindrical illuminance instead of vertical or horizontal, at least when it comes to pedestrians and crosswalks. Vertical is too two-dimensional, where semi-cylindrical picks up reflected light coming from different directions. With the new perspective of contrast-based metrics and more empirical data, we can all have a greater understanding.