Questions and answers: Lighting and lighting control design

Lighting insights

• Side-lit zones involve light penetrating a space from a window in a wall, commonly seen in offices, while top lit zones use skylights or clear stories to spread light in all directions, thus creating different design rules.
• As an electrical engineer, the responsibility for lighting control system sequences of operation falls on the engineer, but an optimal design involves collaboration between the engineer, client and the design team.
• UV lighting, providing an extra level of cleanliness and sterilization, can be beneficial in numerous spaces, while energy savings for clients can be demonstrated through a payback analysis including factors like maintenance costs and energy rates.

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Michael Chow, PE, CEM, CxA, LEED AP BD+C, principal at Metro CD Engineering LLC and Tony Staub, PE, LC, lighting design lead/electrical project engineer at Specialized Engineering Solutions answer questions various lighting and energy codes in the Consulting-Specifying Engineer webcast “Lighting and Lighting Controls.” To read the other portions of the webcast, check out part one and two.

The following is edited for clarity.

Consulting Specifying Engineer: What are side-lit and top-lit zones?

Tony Staub: Side lit zones are probably the most common. What’s happening in the side lit zone, is when you have a window in a wall that going to be serving your space. The most common application is going to be with your 10 by 12-foot offices on the edge of a building that have a window in them, that is going to be a side lit space, because the space itself has the window on the side of the room. Deep into that space, you’re going to have a defined side lit day lighting zone. The light from that window penetrates so far into the space. There are two great examples for top lit zones, and that would be clear stories for skylights. There are different rules for how you are designing your daylight zones under a clear story or a skylight that’s a top lit zone. Those are typically going to be in all directions from that top lit or from your, if you have a skylight, it’s going to push light in all directions below it. If you have a window, it’s really pushing from the exterior into the space. Side lit is typically going to be a window. Top lit is typically a skylight or a clear story.

Consulting-Specifying Engineer: As an electrical engineer, do you look to the architect or the lighting designer to layout the ceiling and the lights to determine the correct lighting levels and exit and emergency lights?

Michael Chow: For certain type of projects, the architecture firm, sometimes they may have their own lighting designer. From my experience, the architect or their lighting designer lay out the ceiling and they pick out the lighting fixtures that they want. If there’s any specialty lighting fixtures that they want, a lot of times they’ll show me a website or a page out of a magazine and they’ll say, “Hey, I want this in particular, this fixture.” One of the things that they usually don’t take in account is the illumination and the energy used by those light fixtures. One of the challenges is to be able to still meet the energy code, the construction budget, and still be able to achieve the recommended foot candle levels.

With the first step I usually take is to start the comp check. What you don’t want to do is wait till the end of the project to do your comp check, and then you find out that the architect and our lighting design, these special lighting fixtures, we can’t use those because we’re way over our watts per square foot allowance. Those are items that should be part of ownership project requirements. By doing the comp check early and working with the architect and lighting designer, you can potentially accept or tell the architect or lighting designer that that doesn’t necessarily work because of either the cost or because of the watts per square foot.

Consulting-Specifying Engineer: Who is responsible for the lighting control system sequences of operation?

Staub: I would say that ultimately, the engineer’s responsible for that. The person that’s specifying the lighting control system is responsible for creating the sequence of operations. However, I’d like to put a little asterisk on that answer. We should be the ones that are understanding all the code requirements and that is going to drive a lot of the sequence of operations. A lot of times your clients are just wanting you to do code minimum. If you do have a client that isn’t interested in going past code minimum isn’t interested in the additional benefits you can get from a more advanced lighting control system, then it might be possible for you as an engineer to completely own that, given you have a building schedule, because that is usually an important piece of the sequence.

The best way for that to be put together is a collaboration between the client, the facility director or whoever that is and the engineer so that you can start to talk about those desirable things that you can do in addition to the code. What are your schedules? Do we need to have multiple layers of schedules? Does your building want to have a morning, day, night, late night sort of thing? If I don’t have that information from an owner, I’m going to make my best guess. Maybe you’re building really operates in more levels than that. It is the engineer’s responsibility; however, you get a lot better product if it’s a design team responsibility that everyone’s involved in.

Consulting-Specifying Engineer: What was the most complex lighting design project you’ve worked on?

Chow: One of the most complex lighting projects that we worked on was for a library and they wanted to see the emergency lighting, not just the fixtures, but they also wanted to see, there’s what’s called a point by point, which I think most electrical engineers are familiar with. It basically shows you the lighting levels. With the software, you could tell it to provide the levels at a particular height, whether it’s the workstation height or at the floor with emergency lighting. What made that project challenging was the plans examiner required that, but then the owner required multiple renderings using different types of lighting fixtures. It was for a particular university in Ohio and they required a special fixture made up of specialty LEDs.

We had to model this, and we also had to design it. Once we did all that and we thought this was going to be manufactured and put in, it got value engineered out of the project. I think we heard that term value engineering quite a bit and after spending all that time on it, it would’ve been nice to see the finished product. There’s some basic software that you can use to provide those illumination levels, but when it comes to modeling, sometimes you must use a more robust and usually that means more expensive lighting software.

Consulting-Specifying Engineer: Do you have a complex project that you want to tell us a little bit about?

Staub: I think there’s a huge list of different complexities I run into, but I think the one that comes to mind just right off the cuff, would be, if you’ve ever done lighting in a mass timber building, they can be very difficult to coordinate. Working on a university building that was going to be built mass timber with a lot of that exposed. The problem is, we don’t want to have surface mounted conduit all over the place and there’s this beautiful mass timber that we want to keep. But what that does is makes it a lot harder to do things like codes, even to do suspended fixtures. You might be drilling through the floor slab of the floor above and using essentially a floor box or poke through to feed that device, right? Because you can’t just core through the mass timber. If you don’t want to have exposed conduit everywhere, you must really think carefully about what lighting tools you’re using and how you get power to your lights in a situation like that. So, I thought that was a fascinating challenge.

Consulting-Specifying Engineer: What are some UV lighting applications?

Staub: Yeah, absolutely. Near UV lighting has been around for a while. That was starting to make some waves a few years before COVID happened. What you really saw as soon as COVID hit, was this industry shift to what can we do to help the world deal with this pandemic? That’s where you saw a revival of UV. We’ve known as a scientific community that UV has helped for a hundred years, but it’s being more well understood. The problem with us not putting it inside of buildings, is that a true UV light can still be dangerous. There’s a lot of products now that are built with a lot of fail safes to ensure people don’t get the dangerous UV arrays.

There’s also filtered UV products now that is out, that is safe for people to be under during certain times, but really what you’re going to be looking at is any space where an extra level of cleaning or cleanliness or sterilization is going to be beneficial. Now, where That’s helpful with any type of project. Do a lot of health care, an infectious control patient room, great spot for it. The way that’s typically done is going to be that a UV light will be at some height within the space and warm air will rise with all the viral load and everything in that space. The UV light purifies or sterilizes that, and then mechanical ventilation goes throughout the space to do the clean hair.

Consulting-Specifying Engineer: How do you show cost of energy savings to a customer?

Chow: That’s a great question. In Ohio with state projects, we must be able to show a payback analysis that whatever lighting pictures you’re putting in and there will be a five-year payback analysis. What is included in that calculation? You’ll have to find out the cost of energy that. Find out who the power company is and typically find out from the owner what rate they’re paying. If it’s more than just five years with a cost analysis, we want to include the maintenance costs in there. One of the things about LEDs is that people think they’ll last 20,000, 30,000, 50,000 hours. It’s been my experience that usually the driver doesn’t last that long. We factor in the cost of replacing a ballast and we can get the cost of the facility’s person that’s working for the owners. We factor all these items into our payback analysis and our energy analysis. That gives the owner or client a bigger picture of the energy savings and operational savings.

Consulting-Specifying Engineer: What CCT do you recommend for health care specifically?

Staub: That is a very good question. If it’s up to me to decide when I’m designing, I will typically go with 4,000 Kelvin, and here is my reasoning for that. The way that our eyes perceive light, the way that the human eye is perceived is that a higher color temperature that more blue is perceived as a brighter space. There is then a theoretical benefit to having higher color temperatures, because you can perceive that as a higher brightness. Then there’s also that humankind tends to feel a little bit less comfortable once you start to get to a high color temperature, 5,000, 6,000, 6,500 Kelvin. I see 4,000 Kelvin as a really compromise between good perception of brightness and comfort, and that’s where I’m shooting for.

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