The lobby of a building is the first place we see when we step through the doors and the last place we see when we leave. Whether the building is for the exclusive use of a single company or it houses many tenants, the lights are expected to be on when someone is there—literally. In some places, that could mean constant lighting 24 hours a day. But how you control your lights has an impact not only on how welcome your building’s occupants feel, but also how efficiently your building runs.
Building codes drive many decisions made about lighting controls. These decisions are further dictated by the choices made during the initial build-out. The controlling version of these codes and standards depends on the state or other governing body with relevant jurisdiction. Over time, building codes have limited the amount of space that can use a single control to a smaller and smaller area. So, how do we make these controls work seamlessly in the lobby?
Daylighting—the practice of incorporating natural light in a space through windows and skylights, for instance—has increasingly become a part of modern lighting design and a focus of many renovations. When done right, incorporating daylighting can lower your energy usage, decreasing costs and increasing your sustainability efforts. This is where commissioning can be crucial.
It can be tempting to try to "design around" daylight, but this will result in a dark space. The key is to design the space in a way that works when there is no light. This may be first thing in the morning or late in the day, especially in the winter months. Properly spaced daylighting sensors will take into account how much lighting is provided by daylight and adjust. A commissioner can double-check that the space is receiving the right amount of light.
Since lobby lighting is being controlled in increasingly smaller areas, primarily via occupancy sensors, if someone is present, then that space is lit. This includes emergency light service per ASHRAE Standard 90.1-2019. Emergency lights always allow a person to safely exit the space, which solves the problem of what happens if the lights go out on an occupant.
If your lobby is occasionally sparsely populated, modern lighting systems can be set up to drop to 50 percent power during a period of no activity (up to 20 minutes). Because of a quirk of human vision, 50 percent power results in 70 percent perceived light, according to the Illuminating Engineering Society of North America. However, once someone enters the area, the lights will automatically return to full power. This works best with dimmable lights, which are commonplace with today’s LED lighting. This is required by ASHRAE 90.1-2019 and is allowed under the 2018 International Energy Conservation Code (IECC).
On the other hand, if you have a well-populated space, timed sensors will be less effective, as there will always be someone in the space to activate the sensor. An alternative solution for lighting use reduction, especially if you have a 24-hour manned space, is to create a schedule. For example, if you set a building’s lighting downtime from 10 p.m. to 6 a.m., over the course of a year, that saves 2,920 hours. Setting the downtime from 8 p.m. to 7 a.m. saves a total of 4,015 hours. If we apply this same scheduled downtime to a 10,000-square-foot lobby at 0.7 watts per square foot, that’s 7,000 kilowatt hours (kWh) saved every year over the initial time frame.
Regardless of how you schedule your lighting system downtime, it’s important to replicate this schedule day after day without the need for personnel interruption. Keeping a detailed lighting keyplan of the areas is vital to allowing building staff to make adjustments quickly and easily. This method works particularly well with a lobby that needs to meet IECC regulations as well. This way, the lobby is lit anytime someone is there, and is not lit unnecessarily to full brightness when someone is not.
ABOUT THE AUTHOR: Susan Martig, senior project engineer with ESD Global, is a lighting and lighting controls specialist with more than 20 years of experience.
This article was originally published in the January/ February 2020 issue of BOMA Magazine.