Proceedings of: Workshop on Improving Building Design for Persons with Low Vision
James E. Woods, Ph.D., P.E. Natural Lighting for Persons with Low Vision
Introduction
I’m going to take a little different approach and look at [natural lighting] from an engineer’s perspective. I’ve been hearing a lot of architectural perspectives around the table. So this may be somewhat different, but I do want to get this point brought forward.
Comment by Tom Williams: Can I make a comment first? We’re not ignoring engineers’ lighting in buildings at all. And there is an interface between nature and harvesting daylight, as Greg was talking.
Response by Jim Woods: That requires an engineering [i.e., quantitative] solution.
Comment by Tom Williams: And then the engineering solution for the interior space where daylight can[not penetrate], which we’re not ignoring that, and that’s part of the equation.
Response by Jim Woods: We’ve got an [engineering approach for] the envelope, too.
Primary Design Issues (slides 2 and 3)
Function
The first thing we have to understand is what’s the function of the occupied space? If you look at the two photographs on the side here (slide 2), these are from Post-Occupancy Evaluations. One is a library area in the courthouse, and the other is a courtroom – two very different functions that are not necessarily [the same as] for office spaces.
View
Viewing outside is important, but if you look at those two pictures, you get a distorted or veiled view from the courtroom which you may not want to have because people are trying to concentrate on what the issues are in the courtroom. Lawyers are facing a little bit of glare there and so is the judge. In the library, depending on how rare the books are, daylighting can be a real problem.
From a thermal aspect, the upper right photo shows a huge curtain wall with the shades pulled and with fluorescent lights turned-on all over the place. Now, how much energy are we saving with that, and what good are we doing with that kind of a design?
Those shades – there’s a point I want to make that’s really important: When you do daylighting and you resort to shades, the heat gain is being transferred inside the building, and that’s got to be dissipated and the view is distorted. There is no energy savings from that daylighting when you’re just transferring the heat in a different way. There is so much myth about energy savings with daylight. There’s plenty of reasons to use daylighting, but daylighting is not a method to save energy. The other issue is: what happens if you don’t have daylight and you need the function? You still have to have lighting provision for the functions. So we need to get to the first issues.
Design criteria
We talked about criteria a little bit yesterday and I’m going to talk about it a little bit more in a few minutes, but I think the three parameters (i.e., luminance, contrast, glare are very important). Now Mariana has brought a fourth one in, and I’m thinking that’s critical, the brightness of the light, whether its luminance or illuminance. And timing: I think timing is a big issue that has to be brought into consideration.
I have a fundamental design question: How would you design differently if you knew the people in the space were going to have low vision? I don’t know the answer to that. I don’t know whether people are going to have low vision in the space or not. So, what criteria do you use to accommodate low-vision persons?
We have to integrate daylighting with electric lighting, for obvious reasons. There’s going to be impact on health. And thanks to Mariana, I think we’ve seen some additional issues with regard to health and circadian patterns.
Impact on thermal and energy consumption
Basically, we’ve got to look at the whole picture, and daylighting is one aspect that’s got positive and negative attributes that we have to understand.
Federal Requirements (slide 3)
This is a statement of the Guiding Principles that are mandated now by federal law. EISA 2007 requires [incorporation of] five Guiding Principles. But read this one: “Achieve a minimum of daylight factor of 2 percent, excluding all direct sunlight penetration (whatever that means) in 75 percent of all space occupied in critical visual tasks” (whatever that means).
Also, “Provide controls, or accessible manual lighting controls, and appropriate glare control”. Now, how can this Guiding Principle be achieved while accommodating for low vision?
I know of at least two fundamental definitions of daylight factors. Somebody questioned a minute ago: What is the ratio of daylight on the surface, horizontal surface, to the lighting level that you want inside? That’s a daylight factor.
If you’ve got 10,000 foot-candles on your concrete outside the building, with the 2 percent daylight factor, you’re going to have 200 foot-candles inside. Now, penetrate 75 percent of your space with 200 foot-candles and you’re going to have a lot of glare.
The other definition is the amount of light available on the glazing, compared to your surface area. There’s a big angle [factor] difference there (e.g., 90 degrees).
We’ve got to be able to come up with consistent measures, but this kind of thing is going to kill us. Think of a 50,000 or 100,000-square-foot footprint of a building and try to penetrate 75 percent of that area. Okay, you can do it in a residence, you can do it in a small space, but try that in a big space. It’s practically impossible. And yet, that’s federal law.
Comment by Tom Williams: One of the things that used to happen in the days before central air conditioning was, our [GSA Headquarters] building, which is on the Historic Register, is designed [around] a series of courtyards. The office space itself, from the corridor line to the window line – the windows were large. The doors had transoms and natural ventilation. There was a large number of windows. You’ve got with Washington – much of it is sweltering during the summer, high humidity. But the courtyards provide a source of cross ventilation and enough light to enter the space, so that every office space, I mean, this side [of] that main corridor line, – the building’s shaped like an E. So you have two interior large courtyards, and the corridor lines were aligned so offices on both sides could all have windows, which allow natural daylight to come in and the cross ventilation.
Without having the mechanical systems, without having all the sophisticated lighting systems, there still were ideas in the way the building was designed that expressed, that captured [the daylighting concept]. And I think, to a certain degree, we’ve changed that building in hideous ways over the years. I mean, we’ve dropped the ceilings, we’ve closed the windows, we’ve gotten rid of the transoms, we’ve made the building something other than what it was intended.
Response by [Participant]: You’ve got huge thermal implications of that in the Washington, D.C., area. Try naturally ventilating the space in August and see what happens to the humidity level.
Comment by Tom Williams: With transoms, there was air movement. It wasn’t stagnant.
Response by [Participant]: Even though it was so humid there.
Comment by Tom Williams: Right.
Comment by [Participant]: You know, architects then, they had a better understanding of how nature interplays into design of a building. That is a big challenge.
Let me bring up a couple points again (slide 3). The top picture here was from a walkthrough that we did during one of the workshops that the GSA HVAC Excellence Program sponsored. The photo is focused across what was called a “security pond” in the front entrance of a courthouse, [with] about eight inches of water in it. Notice there are no hand rails around this thing. Also notice that somebody could walk right into that pool of water. The disorientation is caused by a reflection in that pond of the buildings from across the street. Now, that’s the kind of daylighting I think we need to figure out how not to do.
I want to point out the lower picture, because this is really important. Greg showed one very similar to this. Notice, this is an office. We’re looking outside, huge glare. You notice the shade is pulled down to about eight inches from the desk. Now, the reason for that is it couldn’t go any farther because the full extension of the shade was “value engineered” out of the project.
There was so much solar gain coming in those windows that people kept those curtains pulled all the time. And talking to the occupants, their offices were almost unworkable.
Glare Criteria (slide 4)
All of the measures, with which I’m familiar in environmental control, are based on psychophysiology. If we look at thermal conditions, we consider operative temperatures, which is a function of the perceived dry-bulb and mean-radiant temperatures. If we talk about sound, we consider decibels related to the sound pressure of the ear. If we look at some of the work that has been done on air quality, we consider decipols, which are perceived units of odor. These parameters are all based on perception.
We don’t have very much in lighting, but we do have some. As shown in slide 4, I found at least three references and I think we’ll find a whole lot more when we look at that. You’ve got the references in your handout (Appendix D) of what is called the glare sensation vote.
The other factor is the Daylight Glare Index (DGI). The work that came out of the British Research Establishment in the ‘50s and ‘60s resulted in the Hopkinson Glare Index, which is basically part of that equation (slide 4). Cornell University expanded that to include a daylight component. Although the equation does give quantitative information, there’s a problem with this definition because of terms in the definition must be resolved.
Now, Bob Massof mentioned yesterday three kinds of contrast ratios, he used the Weber equation and the Michelson equation. This brings up a big issue. When we start dealing with psychophysiological relationships and the glare index, look at the equation just generally. The numerator is the luminous level from the source. The denominator primarily is the luminous level from the background. So that is like a contrast ratio. It’s not like the Weber equation. It’s not like the Michelson equation. We need to be consistent in our terminology.
The other thing is the little term “omega” in the equation. It’s almost mythical from the standpoint that it is the solid angle between the eye and each source of light divided by a position index. And, according to the references, you can approximate the position index with the inverse square law: the area of the source divided by the square of the distance to the eye. But it is the solid angle, which is measured in steradians. The denominator is the steradian. It’s not the tangent function that Dennis was dealing with; it’s the solid angle.
Comment by Bob Massof: I don’t understand how you’re summing logs.
Response by Jim Woods: Well, there’s summing across the sources.
Comment by Bob Massof: There’s summing across sources, then taking the log with that?
Response by Jim Woods: Yes. Right.
Comment by Bob Massof: But what’s the 1.6?
Response by Jim Woods: Fudge factor.
Comment by [Participant]: Fudge factor, yeah. They’re playing around with these terms. They’re empirical. They’re not all first principles.
Comment by [Participant]: So is that [exponent] 1.6 supposed to be a brightness representation?
Response by Jim Woods: Yeah, right, exactly.
The point I want to make here is that in some of the references, a correlation has been [reported] between the [glare sensation vote] and the [glare index]. So you can calculate these indices, and you get up to a number like 24, which is a threshold of discomfort, or 28, which is the threshold of disability glare. Yesterday, Dennis was talking about the ratio of the light that’s being received in the cones divided by the total amount received by the rods and cones.
So physiologically, I think there’s a relationship. That’s a research gap that needs to be worked on. But we can begin right now by saying we have some understanding, and in Europe and in Great Britain, they’re actually using this procedure for design.
Now, with our computer power, we could take this on a point-by-point analysis, and we can spread that across the space and do the analysis to understand what kind of glare we would anticipate in a given room.
The CAD models and the Radiance models apparently are informed by this equation, and EnergyPlus and a couple of the other energy programs apparently do have this equation incorporated into them.
So, from an objective standpoint, if we want to get repeatable, reliable, valid data, we can do it. It’s going to take some research, but on a guideline basis, I think we’ve got enough information right now to say we can get started. And you can look at the criteria that are established by the CIE in Europe.
Examples of Occupant Responses from Post Occupancy Evaluations (slide 5)
The last slide I want to show you is a composite of some data that we took during four PostOccupancy Evaluations. In these POEs, we conducted surveys of the occupants and then we walked through the spaces. We tried to understand how the systems were actually performing. These are the four different buildings. Some of the factors that we looked at were overall satisfaction, daylighting, artificial lighting, accessibility, view, aesthetics, acoustics, security and temperature.
The goal is have a minimum of 80 percent of the people in the space find the environment “acceptable,” which gives us a 20 percent area to play with. But if you look at the numbers, the only factor that came through at 80 percent for all four buildings was security. People felt very secure in the buildings.
Comment by Marsha Mazz: Just a point of clarification. You said the only one that came in at 80 percent was security. Did the others come in above or below?
Response by Jim Woods: They’re [mostly] below.
Now, we’re badmouthing daylighting and artificial lighting and stuff like that in this workshop. Put in perspective, we’re supposed to know what we’re doing with the thermal environment. Look at that last column, last set of data.
Comment by Marsha Mazz: For those of us who can’t see the last column, please describe it.
We’re running somewhere between 30 and 70 percent for thermal acceptability in those four buildings. The daylighting is running somewhere around 60 to over 80 percent. Artificial lighting is running somewhere around 60 to 90 percent. So people are not thrilled. We’ve got room for improvement in all of these factors.
The other point I want to make here is we can only get that information in Post-Occupancy Evaluations. And partly, the architects don’t like us because we go back. I was interviewed one time for a professorship at a famous university that shall remain nameless. We got into one huge argument about the concept of design: “where does design end?” My point was design is not complete until you’ve done a Post-Occupancy Evaluation, until you get feedback to know what you did is right. Grand Rounds, right?
Comment by Dennis Siemsen: Yeah. In medicine, we do what we call M&M’s, mortality and morbidity conferences. You know: What’s your outcome? What did you achieve and what you wanted to? If something didn’t work, why didn’t it work and how are you going to fix it next time?
Comment by [Participant]: And we [designers] don’t. We go onto the next project and ‘know’ that what we did was good.
Comment by [Participant]: It’s a major problem at GSA– I don’t want to be quoted on this – but the leadership on excellence and that part of our organization is more concerned with appearance and with awards than it is with whether buildings work. The bottom line is, a lot of our buildings don’t work. And the way you can find out if they work is by doing POEs.
Comment by [Participant]: So therefore, the way you suppress that, so that you don’t know whether the building’s a success or not, is simply not do one, or you commission one to be done, then you take the results of that POE and you put it on a shelf or lock it in a closet and you forget it was ever done.
Comment by [Participant]: And I’ve seen that -- I saw that happen at GSA because of the attitude of the leadership. The POEs were commissioned -- and Vijay’s very much aware of this. The bottom line is, POEs are supposed to generate lessons learned. You’re supposed to take what you learned about your mistakes in design, apply those to the next building you design, so that you have some markers there of things you don’t want to do and repeat again.
Comment by [Participant]: In the central government, we tend to repeat the same mistakes over and over again because we don’t learn from our mistakes and grow from them.
Comment by [Participant]: But that also works into the way you actually produce buildings. I mean, you have a funding cycle, which may start seven years before you start laying bricks. Decisions are made there. And then by the time you actually want to apply lessons learned, you’re so deep into the committed process that there’s no way -- the government doesn’t allow itself to stop.
Comment by [Participant]: OBO ran into the same thing with the standard embassy design, things like the giant atrium that they had between the two big building bars. And we told them – they did about 50 of these things when we were telling them in value engineering workshops this thing is more of a liability from a space use and energy and other things than it is a benefit. And it took them about 50 of them to finally cycle through and say we’re going to take that out, we’re going to make a gallery and take out the atrium because it’s not very useful to us.
Let me mention one other thing that is really bad, and this is the misrepresentation of data. What I’m showing you here are real data from real buildings. What we’re seeing is a preponderance of right now -- primarily, I think, the GSA work, but a lot now is coming out of FEMP in the Department of Energy – they’re normalizing the results from specific buildings and comparing them to normalized national averages. Therefore, you have no clue on a building-by-building basis what’s happened. So there’s no lessons learned. What it does is, it justifies what they wanted to hear.
Comment by [Participant]: Well, it’s even worse than that. They compare it to a database called CBECS, which represents everybody’s buildings. Private sector includes old buildings, new buildings. And, of course, energy performance [i.e., consumption] in that [database] is much higher. What they don’t do because the four agencies –the great thing about four agencies is they all have criteria. They’re not commercial buildings that just depend on the building codes and the design team to develop whatever the performance requirements are. [The agencies] have criteria that you have to meet, and they can move that performance up or down, depending on what the necessity is.
If you compare these new gold and platinum [LEED™ certified] buildings to other GSA buildings, there’s no increased value.
But if you compare energy consumption data from GSA buildings to CBECS data, there’s dramatically increased value. But GSA has been doing good buildings, energy-wise, for many years because they had good criteria. If you follow their criteria, you’re going to end up with good buildings. It’s where the criteria are void that you have issues.
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