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Thursday, September 12, 2013

Turning Up The Heat: Building Glare That’s More Than A Nuisance

The Walkie Talkie Building in London. (Simon & His Camera/Flickr)

The Walkie Talkie Building in London. (Simon & His Camera/Flickr)

It’s a simple rule of architecture: your building can’t damage other buildings. Or parked cars. Or passersby.

And yet in London, reflections from the Walkie Talkie Tower recently melted part of a Jaguar parked nearby.

And in Dallas, reflections from the Museum Tower complex are overheating the adjacent Nasher Sculpture next door. There are other examples of this phenomenon as well.

So why is this happening?

“You have a surface that acts as a mirror — that in itself is not a problem,” MIT architecture professor Christoph Reinhart told Here & Now.

The problem, Reinhart says, is when the mirrored surface of the building curves inward, so that it “acts as a solar cooker,” reflecting concentrated sunlight — which can contain large amounts of thermal energy, or heat — onto neighboring objects or surfaces.

The other effect, which causes glare, is when a surface scatters light. This scattering happens because glass buildings have a reflective coating applied to the glass. Without the reflective coating, the building would absorb most of the energy from the sunlight.

Reinhart says architects and design teams that plan to use reflective surfaces need to be meticulous as they plan their projects.

And it’s not just buildings that cause problems. Reinhart once worked with a Massachusetts airport to resolve the problem of photovoltaic cells causing glare for air traffic controllers.

He used a computer-based method called ray tracing, which models what glare would look like for an observer at every hour of the year.

“We have to use more advanced methods to design the buildings, and avoid these types of incidents,” Reinhart said.


  • Christoph Reinhart, architecture professor at MIT, the Massachusetts Institute of Technology.



This is HERE AND NOW, and if you live in a major city, and there's a new building going up, chances are pretty good it's made of glass. It helps with energy efficiency, and it looks kind of cool and modern. But there is that simple rule of architecture that has to be considered. A new building can't damage other buildings or parked cars or passersby, which brings us to London where, as you may have heard, the reflective glare from the Walkie Talkie Tower recently melted part of a Jaguar parked nearby.

A similar scene is playing out in Dallas, Texas, where reflections from the Museum Tower Complex are overheating the Nasher Sculpture Center next door. The phenomenon has also been seen in Las Vegas. Well, Christoph Reinhart is trying to do something about it. He teaches architecture at MIT and has figured out a way to predict the kind of glare that will result from a glass building. He joins us in the studio.

And Professor Reinhart, how common are these reflections, these so-called death rays?

CHRISTOPH REINHART: Well, these death rays, that's of course one term that's now being used for when you effectively have a large specula surface somewhere in the built environment. So what this means, you have a surface that acts as a mirror. That in itself is not a problem.

So there are two effects that can happen. One is if the surface is curved in a certain way, concave so it's focusing, and that's the case for the Walkie Talkie Building, for example. And what happens then, the building acts as a solar cooker and basically concentrates the solar gains from the sun and heats up at the point.

There's actually another very interesting effect that can happen, and that is when the surface is scattering. So instead of acting just as a mirror, where just one ray gets reflected in exactly one direction, you can have scattering of light forward. And what happens then, you suddenly have a very, very large, bright surface, which is creating glare.

HOBSON: And so how common is that?

REINHART: Well, the reason for that is that if you have just, as we have in many instances in the built environment, a flat surface that reflects some light, then we see a tiny dot of the sun, and that's not a problem because we have the sun in the sky anyhow.

Once we have the scattering effect, suddenly the sun is blown up in size of what you see. And since the sun is several orders of magnitude brighter than the sky, even when you basically smear out the light from the sun when you have this very bright object in your field of vision, then you're experiencing glare, and you can't see. And that is really becoming a bigger effect in - with the installation of photovoltaic panels that have this behavior.

HOBSON: So I think of all the buildings these days that are being put up, many of them made with glass on the side of them, I think of the new World Trade Center in New York, the new Trump Building in Chicago, the new Ritz-Carlton in downtown Los Angeles. Are all of these buildings susceptible to this kind of thing, or are they using glass that's not going to be a problem?

REINHART: Well, in that case it depends really on the geometry of the surface. So when you have a flat surface, you usually have less of a problem. An exception might have been the Nasher building, the...

HOBSON: In Dallas.

REINHART: In Dallas, the sculpture garden, because what happened in that instance, they had a very high reflective material that creates glare in the adjacent sculpture garden. So it's this fine trait of why do we use these high-reflective surfaces. The reason is, of course, when you have a surface, a façade with a lot of glass, then you don't want all these solar gains in the building. So you use - you pick a glazing that keeps the solar gains out.

HOBSON: To keep the building cool, even, right, or not have people's work be affected by the light.

REINHART: Yeah, we are creating our own problem there. So instead of having a smaller window, we have a very, very big window, and then we don't want the solar gains in there, so we are reflecting it out. That of course means we have an impact on our environment that we have to assess somehow.

HOBSON: And is the effect outside just an annoyance, or is it a real problem?

REINHART: Well, it really depends on the application. I guess now the Walkie Talkie is an extreme, where really you have this concentrating effect that destroys objects. That's of course not OK.

HOBSON: Yeah, that's going to be a problem, right.

REINHART: Then in the case of a project that we recently worked on with a local airport, there actually the photovoltaic created so much glare for people in the control tower that they couldn't see. So depending on the situation you can have something very similar going on. If you put photovoltaic panels near a highway, then of course the glare is a safety hazard.

HOBSON: Now tell us about the work that you have been doing because you were actually hired by this airport you're talking about to deal with this exact problem.

REINHART: Yeah, what we have been doing, we have been developing computer-based method, something that is called ray tracing, in order to predict this type of effect. Ray tracing means that in the computer, you basically put a three-dimensional scene of the environment, and then you shoot rays either from the eye of an observer or from a light source that gets reflected, and then you understand what's happening within the environment.

HOBSON: And does that work? Is that accurate?

REINHART: That works. It's very accurate. Typically this technology we've been using, for example, for the design of green buildings, when people do computer simulations of the predicted energy use of the building or of the predicted daylight distribution within the building. There we know that these kind of methods work. Now what we really have to do is we have to look at the whole year. So we basically have to repeat this ray tracing one for every year when the sun is above the horizon in order to see, of course, when can this happen.

And this is where I would say current standards are not there yet to requiring everybody to do this type of analysis. So we can't only pick one moment in time.

HOBSON: Well, we are here at the end of the summer. Is this the peak time, do you think, typically, or does it matter? Is it just about where the light is hitting the glass?

REINHART: There is no specific peak time. So in the case of this PV array, we basically showed, we developed a new technique that basically visualizes over the whole year where the glare is coming from. So there there was a very large band of arrays, 15 of them, and you basically see the sun moving across the sky, and you saw that a different panel was responsible for glare different times in the year.

HOBSON: This is, it seems, a problem that we're going to see more and more of because right now everybody wants to build their buildings with glass. Do you think that the problem is going to get worse, or do you think that maybe glass buildings are a fad, and we're going to move back to an era where we have brick buildings and buildings made of other things?

REINHART: I personally don't think glass buildings go away. They are - they enjoy a lot of popularity. A lot of owners like them, generally, as well. It's known that they create a challenge for the design team in terms of visual comfort, (unintelligible) comfort within the building.

I mean, what we have to do is really we have to use more advanced methods to design the buildings and avoid these type of incidences as that happened here.

HOBSON: Well, you're on the front end of trying to deal with this problem. Is the software that you're developing going to become commercial so that everyone can use it?

REINHART: Yeah, that's - all the tools that we are developing are publicly available, usually in open source form, and in order to make them more usable we have commercialized several tools, as well. One of the big challenges that I see is our tools are relatively easy and straightforward to use, and others can generate similar tools.

We really need now manufacturer data because in the case of the photovoltaic panels, we have this forward scattering effect that I mentioned earlier, and that's something that is not required by anybody to measure and provide this information. So even if you are willing on the design team, you have to basically know the physical properties.

And we looked at various photovoltaic array products, and they vary considerably, actually.

HOBSON: Well Christoph Reinhart, architecture professor at MIT, thanks so much for coming in.

REINHART: Thank you, Jeremy.


HOBSON: And I have to say, Meghna, the one thing that Christoph Reinhart does not do with his research is solve the other problem with these new glass buildings, which is that the windows don't open.


HOBSON: Sometimes it's nice to get some fresh air into the office.


I'm going to slide the Purell over towards you.


HOBSON: Still to come today, defense contractors who worked with the U.S. government in Afghanistan now hope to cash in on border security measures. That story coming up, but the latest news is next, HERE AND NOW. Transcript provided by NPR, Copyright NPR.

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