Corridor lighting is a big energy user. How would you like to save 99% of the energy required for this important lighting?
I recently saw a beautiful new university dorm for grad students. It is a certified green building (LEED Gold). I was struck by how the corridors are lit. In fact, I was awestruck. I think I have seen the future of corridor lighting, with energy savings of 99%, relative to how we light corridors now. It’s nothing short of amazing. Here’s how they do it.
The corridors have LED “step lights”, lights that are usually used to light steps, but are also used in corridors. These step lights are installed every few feet along the corridor, on each side of the corridor, wall-mounted (recessed), a few inches off the floor. Online, I find similar step lights rated at between 1 and 4 watts. The step lights turn on and off with motion sensors, and so are off most of the time. Overhead, there are typical ceiling-mounted surface light fixtures, but these only are switched with manual light switches, and so are rarely used.
How do the students like the corridor lighting? When I started looking at the lights, one of the students said, unprompted, “I love the corridor lights. If I get up at night to go to the kitchen down the hall, the lights come on automatically, and I feel very safe.”
Let’s estimate the savings. A typical corridor might use 0.6 watts per square foot for corridor lighting, and is lit 24/7. That comes to 5.3 kwh/SF/year for the existing, “baseline” case. Now, for the new emerging design using step lights, let’s assume the step lights use 3 watts each. I measured one step light every 14 feet along the corridor length, and the corridor is 6 feet wide. That’s only 0.036 watts per square foot! Now, let’s assume the motion sensors allow the lights to be on 4 hours per day. (This is likely way high. We have done research that shows corridors see motion by occupants for less than 30 minutes per day. But we need to add time for the off-delay, the time delay that the lights stay on after motion is no longer sensed. See http://www.taitem.com/wp-con…/uploads/Lighting-Off-Delay.pdf I still think that 4 hours per day is high, in other words, conservative.) The total energy use is 0.053 kwh/SF/year. This is 1% of current typical energy use to light corridors!
I like the fact that they kept the typical overhead lighting, in case it’s needed. This allows them to have the installed capacity to meet recommended light levels, if the building occupants want it.
Separately, it’s very important that the off-delay on the motion sensor be set as short as possible. LED lights facilitate this – we do not worry about lamp burnout like we used to do with fluorescent lighting. As mentioned in our prior research, off-delay time settings should be set in the single-minutes range, preferably even as short as 30-60 seconds, rather than up to 30 minutes that is allowed by the energy code and ASHRAE recommendations.
There you have it. 99% energy savings. This is another example of the deep, deep energy savings that are possible if we think out-of-the-box, using emerging strategies for energy efficiency, rather than just replacing low-efficiency products with high-efficiency products, and settling for 20-30% savings. The future is here. We just need to step into it! With step-lights to light the way.
P.S. I’m pleased to announce that Green Building Illustrated has been translated into Korean.