(Clue: That depends)
Ultrasonic
Ultrasonic technology transmits pulses of ultrasonic waves and measures the changes of reflection off a moving target. The fixture incorporating the Watt Stopper® Ultrasonic Occupancy Sensor and dimmable ballast triggers the ballast to full “ON” wattage output when it detects motion. In stand-by mode, it dims down the lamps to 50% of the maximum lamp wattage and uses only 24 watts; in full “ON” occupancy mode, the fixture uses 53-watts. This design is commonly used by many light fixture manufacturers and is typically an expensive fixture.
Microwave
Microwave technology transmits microwave pulses and measures the changes in reflection off a moving object similar to a police radar gun. The fixture with a semi-proprietary Microwave Occupancy Sensor uses one F17 T8 lamp that is “ON” 24/7. When this sensor detects motion, it turns on two four-foot T8 lamps. When the motion is no longer detected, the Sensor turns “OFF” two T8 lamps, leaving the smaller F17 T8 lamp “ON”. In stand-by mode, the fixture uses about 17 watts; in full occupancy mode, the fixture uses 73-watts. This lower cost design is almost 30% less than the version with the ultrasonic sensor and offers a cost competitive advantage over most other manufacturers’ stairwell fixtures as well.
The answer is…
If the lower-cost fixture were the right answer, we wouldn’t offer a higher priced sensor for the heck of it. For a stairwell that is “inactive”, the fixture with the Microwave Sensor (Part Numbers 72002 and 72052) is the best lighting source, because it provides the best ROI. For an “active” stairwell, the fixture with the Ultrasonic Sensor (Part Numbers 72003 and 72053) should be selected, because it provides the higher quality lighting and uses less energy in full “ON” occupancy mode.
End of story about occupancy sensors and end of this blog series about our new Stairwell Light Fixture. Try them. They’ll save you money.