In our June Photo of the Month article, we talked about the daylighting in the Pantheon. Let’s do some numbers just for fun: on a partly-cloudy March day in the mid-afternoon there will be about 1.2 million lumens streaming through the Pantheon’s 700-square-foot oculus. The interior light levels are fine. If we tried to equal that with large metal-halide indirect floodlights, it would take about 15,000 watts. The heat energy in the daylight will be about 10,000 watts. So if heat gain is a negative, the daylight is winning on that count.

But we can make it even better: let’s renovate the Pantheon, so we have glazing, not an open aperture. The right glass can help. First, we’d need to increase the aperture area to compensate for the light transmission of the glass. So we increase the Pantheon aperture to 1,000 square feet to make up for a light transmission of 70%. Now we still have the original amount of visible light, but what about heat? Using a high-quality low-E insulating glass, the heat gain per square foot would be reduced to about 35% of what the same aperture would admit with no glass. So despite the increased aperture area we actually have only half the heat gain of the original open oculus, with the same amount of admitted daylight.

Let’s compare that to the electric lighting equivalent. All of the daylight is going to eventually end up as heat in the space, and so will the electric light and the electricity used to produce it. So with the new glazing our daylight is adding 5,000 watts of heat gain. The equivalent metal-halide system is adding 15,000 watts. So the daylighting is now creating only about one-third as much heat gain as the electric lighting that would achieve the same light level.

So that’s a big win for the daylight, right? Maybe. It’s a win only if we assume that the daylight light levels and the electric light levels are the same, and that’s tricky. Clearly, if the daylight levels are higher there will be more heat gain; if they’re three times higher the daylight will produce the same heat gain as the electric system. This is not as unlikely as it may sound. It’s easy to design an electric lighting system that maintains virtually the same desired light level all the time – it’s not at all easy to do that with a daylighting system.

For the Pantheon, what happens on a nice sunny May afternoon around 2:00? Now we have well over 5 million lumens coming in through the oculus, and even with the new glass the heat energy in the daylight will be about 22,000 watts, or about 75,000 BTU per hour. But the electric lighting system would still be plugging along at the same 15,000 watts. Sure, the daylight level is now higher than the electric light level, but we don’t need that extra light, and now the daylight is producing more heat gain than the electric lighting would. And that means we’re going to increase the amount of energy we have to use to air-condition that heat away (did I mention we’re adding air conditioning, too?). And by June the problem will be even worse.

This illustrates one of the important challenges of designing daylighting: maintaining reasonably consistent light levels at different times of day and different times of year (and also under different weather conditions). There is a related design challenge: maintaining consistent light levels at a given time but in different parts of the space. Because the Pantheon aperture is at the center and high above the floor, light levels at the floor will generally be very uniform (although occasionally on mid-days in summer direct sun will hit the floor, and all bets are off).

But in multistory buildings the daylight often has to enter from the sides, and we don’t usually have 142-foot-high ceilings, so daylight levels near the windows tend to be much higher than those farther away. The issue is the same for both challenges: if we design for an adequate daylight level for less-than-favorable conditions or locations, we can end up with much higher than needed daylight levels for the favorable conditions or locations.

There is also a tendency to simply overdesign daylight levels under all conditions. Our Pantheon example had a daylight aperture of only about 4.5% of floor area: a glass curtain-wall building could easily have a ratio of 40%. Without extensive shading and low-transmission glass, that is very likely to result in daylight levels much higher than needed. And those higher levels bring higher heat gain. They can also be visually uncomfortable, but that’s another subject.

Photo Credits: Irene (2), OliverN5 (3)

I just finished reading Michael Pollan’s book, “In Defense of Food”. Besides being a very enjoyable and enlightening read, I was struck by the parallels between the food industry and the architectural profession. It seems as “logical” beings, we are constantly trying to break down the components of complex systems in order to extract and identify the good or positive elements. Food scientists in the last hundred years or so have been able to identify parts of whole foods such as proteins and vitamins that are supposedly good for us, and to reintroduce them back into our refined and industrialized foods, since processing expels most of these nutrients. However studies have shown that even after adding all of these nutrients back into our processed foods, the original whole food is still more healthful. This scientific reductionism that breaks food into its component parts ignores subtle interactions and context. The whole is worth more than the sum of its parts.

Architecture is also a complex system. There are a host of parallel professions involved with designing and constructing the built environment. Since humans spend a majority of their lives indoors or in a man-made world, architecture too has been analyzed and dissected. But when architecture is evaluated solely on the sum of its parts rather than its synergy of systems, we lose the soul of architecture, the thing that separates true architecture from, simply, a building.
Our latest architectural evaluation system is LEED, essentially a scorecard to evaluate a building’s sustainability. I’m not suggesting that LEED is a bad thing. It has identified many critical elements of design, and made the profession more aware of the importance of sustainability since we’ve been operating in a world of blissfully bountiful energy. But to evaluate architecture solely on its LEED score is like evaluating a meal at a restaurant by how many calories it contains.
Why is it that “eaters” trust scientists or food manufacturers for the “healthfulness” of our eating habits instead of our rich historic culture? Why does a client trust reams of calculations generated by a technician before trusting the good judgment of an architect? Why would a homeowner with a custom addition project hire a builder before (or instead of) hiring an architect? And why would an architect have an engineer or lighting manufacturer’s representative design their lighting?

All of these specialists are important to the overall success of the project. But just as with architecture, lighting design is not only about the numbers. Sure, we have to satisfy certain illuminance and power density criteria, but real lighting design starts with design: a true understanding of the architectural concept and a constant weaving of lighting hardware into the architectural fabric so that, especially in the case of daylighting, the light and architecture are inseparable.
Oil subsidies and unnaturally low energy prices could be blamed for western industrialized food, energy-inefficient buildings, urban sprawl, and the general attitude of us all. Recycling, turning lights off, using public transportation – they’re all contributing to a more sustainable world. With the current economic situation, our design practices have geared up for new challenges in sustainability and energy savings. But designers cannot depend on emerging technologies alone. The real innovations will come from the architects and designers themselves and from how these technologies are creatively employed to produce wonderful environments where humans can flourish and live more harmoniously with nature. Long live design!

Photo Credit: Keith Yancey / Lam Partners Inc (1), Stephen M. Lee (2), Wil Carson / Michael Maltzan Architecture (3), Peter Vanderwarker (4)