Efficient Lighting = Enormous Savings
With the right designs, buildings can cut 40 percent of their lighting costs
Steven Cherry: Hi, this is Steven Cherry for IEEE Spectrum’s “Techwise Conversations.”
The U.S. Energy Information Administration estimates that lighting accounted for 13 percent of the total electricity consumption of the United States in 2010. That’s about 500 billion kilowatt-hours in all.
Spectrum has covered lighting technologies—sometimes obsessively, when it comes to LEDs, for example—but we haven’t spent much time looking at the sometimes high- but sometimes lower-tech ways that real companies are saving real money by putting out fewer lumens in real-life situations.
The publication of a new book, Efficient Lighting Applications and Case Studies, from CRC Press, seems like a good opportunity to redress that.
The case studies look at the use of low-power sensor networks; white light instead of high-pressure sodium for street lighting; and building and architectural designs that make better use of natural light and reflective light.
The book’s editors are Albert Thumann, who’s the executive director of the Association of Energy Engineers, and my guest today, Scott Dunning, a professor and director of the University of Maine’s school of engineering technology. He joins us by phone.
Scott, welcome to the podcast.
Scott Dunning: Good morning, Steven. How are you?
Steven Cherry: Scott, in the real world, architects, designers, and engineers have to balance color attention, color temperature, the life span of a lighting technology, ease of replacement, whether an installation is indoors or outside, and efficacy, which is measured in lumens per watt. And do that for at least seven major types of lighting. Is there any area of technology that has to make these kinds of trade-offs between practicality and aesthetics?
Scott Dunning: Well, you know, that’s a good question. And off the top of my head, I don’t think there is.
Steven Cherry: You have one case study about putting the lighting on a ZigBee network in a parking garage. Now, it turns out that most parking garages are fully lit 24 hours a day, which is quite a waste of energy. Tell us about ZigBee itself and Hills Plaza, which is in downtown San Francisco.
Scott Dunning: Sure. What this report was done, by Professor Wang, he did a study, and this is a case study, showing how we can use the ZigBee communications network—ZigBee’s a standard communications standard—and basically control your lighting more intelligently.
Steven Cherry: So ZigBee is a communications standard that’s sort of like a Wi-Fi. It’s for wireless networks, but much lower power. Is that right?
Scott Dunning: Yes. In ZigBee we’re seeing in, actually, I’ve seen it in grocery stores, for doing ZigBee wireless for some of the refrigeration controls, for example. So it’s starting to be used in more commercial applications other than just lighting.
Steven Cherry: Now, you also had some ZigBee case studies outdoors. There was a network of streetlights in the city of Xuzhou, in Jiangsu province, and then a bunch of other cities in China as well. And they all consistently showed energy savings of about 40 percent. What was involved in those installations?
Scott Dunning: What they were trying to do with the communications was to implement control rather than just having a light sensor to determine when you turned on or off an outside light. And we’ve all probably experienced streetlights in our neighborhood, where they were on and you say, “Gee, it doesn’t seem to makes sense that this is on.” And sometimes it was a sensor that went bad, and so by being able to control, they could actually tighten down the hours of operation and not just base it on an open-loop control, where it was just detecting light level.
Steven Cherry: So in other words, these ZigBee networks basically connect all of the lighting elements, kind of basically back to a master intelligent controller.
Scott Dunning: Yes.
Steven Cherry: Um, so these wireless networks, both indoors, ones like the parking garage and outside, are a lot cheaper than if you were wiring streetlights together, or whatever, with copper wiring or fiber cable. But they’re still an expense. Do have any sense of the outlays for that kind of networking versus the ultimate savings in energy costs?
Scott Dunning: Well, I mean, I could give you a ballpark and say that, my guess is that you’re probably one-tenth of the cost when you establish your wireless network over what a wired network would be. But there’s a lot of different things that can impact your cost. Um, sometimes just communicating wirelessly, going through structures, can be difficult. And so it depends on how many walls and barriers that we’re trying to go through.
Steven Cherry: And what kind of savings in energy are these parking garages and street-lighting systems getting?
Scott Dunning: Well, again, it’s we’re seeing when they put in a significant control, like you’ve shown in these two case studies, you can get upwards of 40 percent energy savings. And usually they’re done, when they put in the control, they’re also upgrading the lighting. They’re using and going to a more efficient technology, which is part of that savings.
Steven Cherry: You have a statistic in the book that 5 percent of all U.S. energy consumption is tied to the performance of windows. That turns out to be the equivalent of about 1.7 million barrels of oil per day. Tell us about windows.
Scott Dunning: If I have a wall with six inches of insulation in it, and I compare it to a window, I can have a very significant difference in terms of insulation level. Now, when you look at the window, you say, “Where is the energy going through?” Well, it goes through the surface of the window, but it also, you get infiltration around the window. So you have your infiltration losses, and you have your radiation losses. When you take a thermographic scan outside of a building, you can clearly identify the windows, and then you can clearly see the differences between using films, using double-paned windows, low-heat glass, things like this, and actually see the temperature differential.
Steven Cherry: But, you know, we love windows. I guess we would feel a little closed in without them. But also they are a source of natural light, and I guess building designers and architects are trying to use more of that natural light.
Scott Dunning: Yeah. Well, you know, it’s interesting. There’s been some new technologies. One, I was just talking with a gentleman the other day about a spray-on coating that you actually retrofit an existing window, and spray it on on the inside to increase its insulation value. And it’s a nano-type-based application. It really…it gives you a clear view through the window but increases its insulation value. So, we definitely like to have the ambient light. Matter of fact, one of the things we talk about in the book is the new technologies where we’re using programmable ballasts, that each individual ballast, say I have a room of 50 lights, each individual ballast going to a fluorescent light is addressable and programmable, and we can adjust each individual ballast light output up and down based on the ambient light level in the room. Or we can program it based on shades that go up and down that are allowing the light to come in, and they’re responding to the ambient light level outside. So, you know, they’re really starting to get some exciting technology involved in harvesting day lighting.
Steven Cherry: OK. A lot of our listeners spend vast portions of their day in front of a keyboard and one or more computer screens. Tell us about ideal task lighting.
Scott Dunning: The author that wrote that specific chapter has done years of investigation in ideal task lighting. And actually, I had a nice discussion with him on the telephone, and he said, “I’m sitting here at my desk, and I have two lamps in my room.” They were each 20-watt bulbs that were ideally placed behind him so that he didn’t have shadow in front of him, and they lit up just the space he was working at. Now, most of us wouldn’t be happy with that kind of light just from the standpoint of, we like to see the whole room lit up. But ideal task lighting is, it examines, where do we place our lights to minimize glare, reflections off surfaces, and shadowing. And most lighting designs involve just installing lights in your ceiling. And what he’s explored is this idea of using lights that are down at floor level and putting them in ideal placement in a space to light up only the work area that you need the light at.
Steven Cherry: Yeah. I have to say that you have a couple of pictures in the book that show this, and they look like, I don’t know, the kind of rays of lights that TV news cameramen or maybe wedding photographers use. It doesn’t look like ordinary office lighting at all.
Scott Dunning: No, it’s very different. And, you know, it’s a matter of saying, as engineers we try to balance what makes the most sense in terms of economics and use the best technology and use as little energy as possible. But at the same time we have to consider the aesthetics and consider what the audience wants. And so the question I think the author’s asking there is, “Hey, can we open up the box a little bit here? Can we look outside of what we’ve been doing and consider more of a compromise here, where we aim this task lighting at the spot we’re gonna need it?” And if you want to use ambient light, that’s fine, but maybe you don’t have to have everything at the same light level.
Steven Cherry: And if you can replace regular lightbulbs with 20-watt bulbs, there might be some savings there.
Scott Dunning: Exactly. Exactly. So it’s savings, not only things you can do at your home, at a residential level, things you can do in your office at a commercial level, and things you can do in industrial facilities.
Steven Cherry: It turns out, I guess, there’s specific design software for lighting that building designers and architects can use. What do these programs do that regular design software doesn’t?
Scott Dunning: What it takes into account is, you’re actually looking at each individual spot in a space, and you’re trying to keep uniform lighting. And so if I have a certain fixture with a certain reflector on it, it has a, think of a radius of where that light’s gonna go. And how do we overlap our lighting such that we keep uniform lighting in the space. And if we don’t do it right, you may have been in a conference room where they have fluorescent lights in troffers in the ceiling, and they were spread too far. And when that happens, then you get a change in light and, depending on where you sit on a desk, you may have good light, you may not have good light. And so the software can really do the modeling for you to take these overlaps into account, which is significant calculations, and allow you on a point-by-point basis to model the whole space and maintain uniform lighting.
Steven Cherry: So I guess in the same way robotic software sort of includes the physics of objects—the weight, and the momentum, and the friction, and so forth—this lighting software includes some of those variables we spoke about at the top of the show: the color retention and the efficacy, and so forth.
Scott Dunning: Absolutely. And really, it allows you to examine, say, “Hey, what if I used a different reflector? What would the effect be? Would that change the design such that I can use less lights? Can I maybe get away with using six four-foot fixtures instead of eight four-foot fixtures by placing them differently and using different reflectors?” One of the things that you face with an LED light is, the light that comes out of the fixture is linear in nature. Now this is great if I’m trying to project light on a spot. However, you don’t get the spread that you do in some of the other technologies. And so, for example, if I were to light up a ballpark, I’ve got some nice images, where they took the existing light and then they put in, retrofitted it, with LED fixtures. And what you see is, the light goes on the ball field, but you don’t get this, what you can think of as “overspray,” into the back parking lots. And so, basically, you can use less light because you’re not putting where you don’t want it, which is a positive. The flip side of that is in places like Las Vegas, where they’ve retrofitted street lights. You get to a corner where a crosswalk is and, if you’ve put in LED, you’re not getting that big overlap. And so they actually have to be very careful for this application to use maybe angling and adjusting the reflector, so that you can light up the sidewalk where you need it and the crosswalk where you need it. Not just the roadway. So LEDs, we’re seeing in lots of different applications, but there is a challenge, and it can be a positive or a negative, with that linear focus of the lighting.
Steven Cherry: And so I guess some of that specific lighting design software might help there to avoid those gaps and make sure the coverage is right.
Scott Dunning: Yes, it will.
Steven Cherry: Well, Scott, I can’t speak for our listeners, but for me, the science and technology of installing lighting sounds even more interesting than what’s done in the research labs, so thanks for telling us about it.
Scott Dunning: Oh, you’re welcome. And it was a pleasure talking with you today.
Steven Cherry: We’ve been speaking with Scott Dunning about the book Efficient Lighting Applications and Case Studies, from CRC Press. For IEEE Spectrum’s “Techwise Conversations,” I’m Steven Cherry.
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