I proposed motion sensors for our library’s study rooms this week, pitching the idea partly on manufacturer claims I’d seen tossed around, savings up to 85 percent on lighting energy. When I actually went looking for independent, published field research rather than product marketing, the realistic number turned out to be a lot more modest, and more useful precisely because it’s honest.
The 15 to 85 percent range does show up in the literature, but it comes with an important caveat attached by the researchers themselves, there is little published research to support the magnitude of those claims at the high end. When researchers actually measured real installations rather than citing manufacturer brochures, the numbers cluster much lower. A field study at Rensselaer Polytechnic Institute measuring occupancy sensors in real classroom settings found wasted lighting energy, the amount actually recoverable through sensors, averaged 25 percent in one school and 15 percent in another. The Electric Power Research Institute and ASHRAE, in generic assessments across commercial buildings broadly, estimate an average 30 percent savings, not the 85 percent ceiling sometimes advertised.
A more recent 2020 study out of a university in Seoul actually measured lecture room lighting with sensors installed versus removed, alternating week by week over a full semester to control for normal variation. Their result, a 32.4 percent savings rate in lecture rooms specifically. Underground parking, a much more consistently unoccupied space, saw a dramatically higher 77.6 percent savings, which helps explain why marketing materials citing 85 percent aren’t lying exactly, they’re just describing the best case space type, not a typical study room with regular but intermittent use.
That context changes how I should be pitching this to Facilities Management. A realistic study room installation, based on actual published field data rather than manufacturer ceiling claims, should target something closer to 25 to 32 percent savings on lighting in those specific rooms, not the 85 percent figure that would make for a flashier slide but doesn’t hold up against independent measurement.
There’s a second complication researchers flag that matters for a shared space like a study room specifically, unowned zones, meaning spaces nobody feels personally responsible for controlling, tend to see smaller savings than private offices, because people passing through are more likely to trigger the sensor without actually settling in to use the room. One study measuring exactly this kind of unowned space found savings ranging from 17 to 53 percent depending on how many different uses the space serves, with multi use areas landing on the lower end.
None of this kills the proposal. A 25 to 32 percent reduction on the $8,000 a year our 12 study rooms reportedly burn through is still real money, somewhere around $2,000 to $2,500 annually, a number I can defend with a citation instead of a marketing claim I’d have to walk back the moment someone on the facilities committee actually looked it up.
Sources. Rensselaer Polytechnic Institute field study; Electric Power Research Institute; ASHRAE; 2020 Seoul university lighting study.