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How Much Energy Are You Wasting Overnight?
Even if no one’s working late, your building may still be burning the midnight oil – literally. Overlit exteriors and lights that are left on could be driving up your lighting-related energy consumption overnight, when little to no illumination is needed.
“Light is wasted any time a person doesn’t need it, either because the space is unoccupied or because more electric lighting is being provided than is needed,” explains Jeremy Snyder, Director of Energy Programs at Rensselaer Polytechnic Institute’s Lighting Research Center. “There are many opportunities to reduce wasted light. Paying attention to these opportunities can result in cost savings.”
Discover where your building is wasting lighting and what to do about it with these tips.
Why is Light Wasted?
Building owners frequently don’t notice that there is a problem, either because lights are left on when no one is around to notice or because they don’t realize that some intentionally lighted spaces are overlit, says Todd Houghton, Vice President of Energy Efficiency at GenPro Energy Solutions, which designs and implements renewable energy systems and energy efficiency projects.
“People drive past their building, see that their parking lot is lit and that’s all they care about because it’s supposed to be lit,” Houghton adds. “Until you actually show them that it’s overlit and they can save money by lowering the energy consumption, they may not recognize that they have a problem because they’re focused on running their business.”
Organizations purposely leave lights on for three key reasons, notes Cynthia Gibson Murphy, Project Manager and Associate Partner at Margulies Perruzzi Architects:
- Safety: “If a space is not equipped with occupancy sensors, then egress lighting may be programmed to stay on 24/7,” Murphy explains. “This can be as much as 25% of the light fixtures in open and circulation spaces inside a building, which can be a fairly substantial load.”
- Security: Exterior lighting is often left on to discourage people from approaching, gathering or loitering, Murphy says.
- Focal points and branding: “Highlighting building features is common,” Murphy says. “Often lights that simply highlight plantings will be on a timer, while others are on daylight sensors. They turn on and increase brightness toward dusk, but actually dim down to reduce glare, intensity and energy when it’s fully dark out and less light is actually needed.”
Interior lights are often left on inadvertently by occupants or cleaning staff, especially if they use manual lighting controls that are in an inconvenient location, adds Snyder. Automatic shut-off controls may not do their job if they haven’t been properly adjusted. Outside, broken photosensors may mean exterior lights stay on when they’re not supposed to, further driving up energy costs.
How to Find Waste
A good first step to identify wasted light is to conduct your own investigation, Snyder suggests. Walk around and observe your property yourself, both during the day and after hours when lights should be off. Alternatively, you can bring in a professional to conduct a comprehensive lighting audit, says Danny Streit, President of Lumen Control Solutions, an architectural lighting design firm.
“Most lighting audits begin because the owner is interested in the energy savings,” Streit explains. “Typically, someone comes on-site in the evening and looks at areas where energy could be saved either by turning lights off, reducing the light output or retrofitting to a more efficient source like LED. There are also metering devices you can install temporarily that measure usage patterns.”
Houghton recommends comparing the light levels in each space to the code for your city, county or state: “Look at the minimum of light you have to have, then walk around the parking lot, sidewalk and sides of the building with a footcandle meter to see if you’re within the codes in regards to minimum light. From there, look at doing other things, like adding controls.”
Identify Interior Issues
Older buildings tend to waste interior lighting energy along any emergency egress paths, especially in stairways and any other places that aren’t regularly used, Murphy notes. Hotels and other hospitality facilities also have to light hallways at all hours, adding additional waste. Lobbies and entryways are also typically lit nonstop.
“MPA has helped property managers add local occupancy sensors on stairwell lights that will turn on as people approach them,” Murphy says. “As these are egress paths and need to be well-lit for safety, it’s important to test out the location of the sensors to make sure they capture people within their view before they get to spaces that are not lit.”
Buildings with older sensor technology (or none at all) tend to waste a significant amount of energy on lighting, but even buildings with newer equipment are vulnerable if the sensors aren’t programmed correctly or occupants override them.PageBreak
“Indoor lighting waste seems to be more prevalent in large open offices with cubicles. They’re typically not controlled properly,” says Streit. “Putting occupancy sensors in a large area like that means they have to be placed properly and networked so that they pick up the motion of someone anywhere in the space.”
Overrides are typically implemented when occupants work late or the cleaning crew enters and the lights have to be turned back on, particularly if existing sensors don’t automatically shut off lights when no movement is detected. “This may mean an entire floor is illuminated while only a couple of people occupy it,” Murphy says.
Adds Houghton, “We see a lot of waste in schools and commercial buildings where the cleaning crew comes in and turns everything on because they don’t want to waste time looking for the switch. Other times the lights just aren’t zoned, so there will be one bank of controls and when you flip one switch, 20 lights come on. It doesn’t make much sense.”
Investigate Excess Exterior Energy
Parking lot and accent lighting are the two biggest culprits outside, mostly due to overlighting, Houghton says. In addition to wasting energy, excess lighting outdoors contributes to light pollution, especially if the fixtures direct light up into the sky or onto neighboring properties. Parking lots in particular tend to suffer from a combination of perception and inefficient lighting sources.
“If you’re looking at a lit parking lot, a high light level may give the owner some satisfaction – ‘Wow, my lot is really secure. I need all that light to blast out.’ That’s not necessarily the case,” explains Houghton. “It’s like how people always think their clothes aren’t clean unless they see bubbles in the water. The quality of the light is a low-Kelvin yellow light, especially with a sodium vapor light where the light is so yellow that security cameras can’t pick up images if someone breaks into a car on your lot. Would you rather have that or an LED daylight-style light where you’re saving money and your cameras can pick up everything? It’s not as intense, but just by changing the color temperature and lowering the light output, it still looks good.”
Popular lamp choices for parking lots, such as HID sources, are often left on out of necessity because once they’re turned off, they require a cooldown time before they can be turned on again, Streit says. “HID sources are not like an incandescent or fluorescent source where you can turn it off and then right back on. That cooldown period can be 10 to 15 minutes, so typically HID fixtures are left on. HID can also create pools of light underneath the pole, which leads to overlighting because in order to maintain the required light level, a higher wattage or additional fixtures are necessary. The LED sources that are used now are about half the wattage of the HID sources for the same amount of light, and those can be turned off or dimmed.”
Smart Solutions for Savings
If you’ve discovered that your facility is wasting energy on excess light, there are several options for making sure lights are turned off when they should be and cutting down the amount of power needed for spaces that genuinely need 24/7 lighting. Consider one of these strategies:
Motion sensing: The lighting system determines when people have entered the space (with occupancy sensors) or when they are no longer present (vacancy sensors) and turns the lighting on or off accordingly. Adding bi-level lighting allows spaces to be dimmed to a lower level when occupancy isn’t detected, saving energy in spaces where codes or building policy dictate that lighting must be left on all night.
“Most spaces should be illuminated only when they’re occupied, and the best way to be sure of that is motion sensors,” explains Snyder. “Vacancy sensors save more energy than occupancy sensors because occupants don’t always need to turn on overhead lights, such as when there’s sufficient daylight, but occupancy sensors work better in common spaces and where needed for safety.”
Outdoor security lighting in parking lots and garages and around the building perimeter can also benefit from motion sensing, Snyder adds. Facade lighting can incorporate an astronomical timer so the building is only illuminated when it’s more likely to be seen.
Time sweeps: This control comes in the form of a relay panel in the electrical closet. Circuits are fed from the distribution panel through the relay panel, which uses an astronomical time clock to turn circuits or relays on and off at scheduled times. “Usually when time sweeps are used, it’s well after regular business hours just to allow anyone working over to get out of the building,” Streit explains.
Metering: Murphy suggests that in the absence of a control system, you can use separate meters to determine the energy load of light fixtures.
Relamping/delamping: Replacing inefficient light sources with high-efficiency LEDs can save a considerable amount of money that can then be reinvested into other lighting improvements if needed. LEDs also offer the benefit of optics that place light exactly where it should go instead of letting it spill out, allowing you to maintain a uniform footcandle level instead of intentionally overlighting to make sure the poorest-lit areas still meet the minimum requirement.
“On accent lighting, we can control where the light goes better with LED so that we can take that 400W area light pointing up at the building and take that down to a 150W LED with optics on it,” Houghton says. “The same is true with parking lot lighting. These days, you can go from 400W to 150 or 200W depending on the lot and code. A parking lot generally requires 0.5 footcandles for security, and you can achieve that a lot more easily with today’s optics and not waste any light. You can also put controls on parking lots – for example, an auto dealership might want to keep the lights at 100% from 5 to 10 p.m. because most people are shopping from 5 to 9. After that, you can dim the lights down to 50%. Someone driving by sees that the lot is still lit pretty well, but you’re saving half the money you were spending.”
This strategy also applies to interior lighting, Murphy says: “An older space that utilizes 2x4 parabolic recessed fixtures with three T12 lamps could use up to 120W of energy and they might be spaced as closely as 6 feet. These could be replaced with newer LED recessed fixtures that use 35 to 45W each and provide even more illumination, so the amount of light output can also be reduced. That results in less glare and fewer hot spots, as well as allowing them to be spaced further apart at 8 to 10 feet. That also reduces the number of fixtures needed to light the same space, multiplied by the lower energy use. The number can be substantial.”
A strong control strategy: Rather than adjusting the lighting controls every time one person makes a request, Houghton recommends developing a single lighting policy covering your entire facility, creating lighting zones as needed and linking every area to a sophisticated control system that can be tweaked remotely.
“It comes down to adopting a strategy with your team,” Houghton says. “You can either provide controls for everyone, or you can say, ‘We’re going to put motion sensors here, here, and in everyone’s offices and you have to be aware.’ All the motion sensors then can talk back to a central control panel that the owner can pull up on his phone or laptop around 6 or 7 p.m. when everyone should be gone. He can see that Joe didn’t shut off the lights in his office, for example, and click a button to turn the lights off. The technology of controls is growing quickly and more features are moving into the lights themselves, which can bring substantial savings, but you have to ask the questions.”
Janelle Penny firstname.lastname@example.org is senior editor of BUILDINGS.