Current building codes require specified time delays before occupancy sensors turn off or dim the lights in an unoccupied space. And while shorter delays save energy, constantly switching lights on and off can shorten the lifespan of a fluorescent lamp, according to a blog posting on the Lighting Controls Association website.
This could change with the uptake of more LEDs, which do not suffer a reduction in lifespan due to frequent switching.
The National Research Council Canada (NRC) conducted a study to determine the ideal timing of office lighting controls, to save energy but avoid the nuisance of false triggering that leaves occupants in the dark. In one scenario, multiple workstations were fitted with dedicated occupancy sensors. Time delays were set at five different intervals.
NRC evaluated energy savings, compared against the traditional approach of centrally controlling all luminaires via scheduled ON/OFF, with the lights operating the full 12 hours. NRC found:
- Scenario 1 (30 minutes), 22% energy savings
- Scenario 2 (20 minutes), 26.4% energy savings
- Scenario 3 (10 minutes), 31.9% energy savings
- Scenario 4 (1 minute), 45.8% energy savings
- Scenario 5 (0 minutes), 48.6% energy savings
NRC concluded the 10-minute delay made the most sense, but added that a detailed cost analysis and human factors’ study of the acceptance of this frequency of switching are needed before application in a commercial building, according to the Lighting Controls Association blog.
Photo of office via Shuttestock.