Sensing Technology Decides Where a Sensor Works
Every complaint about an occupancy sensor traces back to one of two things: the wrong detection technology for the room, or a coverage pattern that does not match the space. Both are decided at the ordering stage, which makes this one of the few product categories where reading the spec sheet properly prevents essentially all of the field problems.
Passive Infrared
A passive infrared sensor detects the heat signature of a body moving across its field of view. The lens divides that field into zones, and movement from one zone into another registers as occupancy. Because it works on line of sight, anything blocking the view blocks detection, which means a PIR sensor sees nothing around a corner, through a partition, or behind a tall bookcase.
PIR is excellent at catching major motion, meaning someone walking into a room, and comparatively poor at catching minor motion, meaning someone sitting still at a desk typing. That makes it a strong choice for small enclosed spaces with clear sightlines and steady traffic: private offices, storage rooms, copy rooms, corridors, and restrooms. It is also the least prone to false triggering, because it does not respond to air movement. Where a room genuinely only needs a manual on and off with no automation at all, Lumera's standard switches collection is the cheaper and simpler answer.
Ultrasonic
An ultrasonic sensor emits high-frequency sound waves and reads the pattern that reflects back, registering occupancy when that pattern shifts. Because sound reflects off surfaces, it does not need line of sight, so it detects around partial obstructions and into the shielded parts of a room that a PIR sensor cannot see.
Ultrasonic is far more sensitive to minor motion, which is exactly what an open-plan office or a restroom with stalls needs. The tradeoff is that same sensitivity: air movement from an HVAC diffuser, a fan, or a door opening can register as occupancy and hold the lights on in an empty room. Keeping the sensor away from air handling outlets and adjusting sensitivity during commissioning is what separates a good ultrasonic installation from an irritating one.
Dual Technology
A dual-technology sensor contains both, and the useful part is how the two are combined. Typically both technologies have to agree before the lights turn on, which eliminates false triggering, while only one needs to detect motion to keep them on, which eliminates the lights dropping out on someone sitting still. That combination is why dual technology is the specification for classrooms, conference rooms, and open offices where both failure modes are unacceptable.
It costs more than either single technology, and on a small storeroom that money is wasted. On a conference room where the lights going out mid-presentation is a genuine problem, it is the correct choice.
Occupancy or Vacancy, and Why Codes Care
These two words describe different behaviors and they are not interchangeable on a job with an energy code inspection. An occupancy sensor is fully automatic: lights come on when someone enters and go off after the room empties. A vacancy sensor requires a manual press to turn the lights on and only handles the automatic off. Many devices do both and are set with a switch on the unit.
Energy codes in a number of jurisdictions specifically require manual-on, automatic-off operation in certain space types, on the reasoning that a person entering a well daylit room may not need the lights at all, and full automation defeats that saving. Confirm which mode the local code requires before ordering, because a fully automatic sensor installed where vacancy mode is mandated will fail inspection even though the hardware is correct. Some of those same code sections are satisfied instead by a fixed schedule, which is what Lumera's timers collection covers.
Wall Switch, Ceiling, or Fixture Mount
Mounting style follows the room shape more than convenience.
- Wall switch: replaces an existing switch in the box, no new wiring, and covers the room it faces. Fast to install and limited to what it can see from the wall.
- Ceiling mount: sees the whole room from above with a wide or 360 degree pattern, which suits open areas, large rooms, and anywhere furniture would block a wall sensor.
- Fixture integrated: built into or mounted onto the luminaire, common on high bays and troffers, and the practical answer for a warehouse where wall or ceiling sensors would need their own wiring.
A wall switch sensor is the obvious first choice on a retrofit because it needs no new cable, but in an L-shaped room or one with tall shelving it will leave dead zones no amount of sensitivity adjustment fixes.
Outdoors the question changes entirely, since exterior lighting usually needs to follow daylight rather than occupancy. Lumera's photocells collection covers that control instead.
Coverage Area and Time Delay
Manufacturers publish a coverage area for each sensor, and it is worth treating that figure carefully. Coverage is usually stated for major motion, with a smaller effective area for minor motion, and it assumes a specific mounting height. A sensor rated generously on paper can under-perform in a room full of partitions.
Time delay sets how long the lights stay on after the last detected motion. Too short and occupants get left in the dark mid-task, which is the fastest way to have a sensor disabled by an annoyed tenant. Too long and the energy saving evaporates. Somewhere in the mid range suits most spaces, with shorter settings for storage and longer for conference rooms. Set it during commissioning and revisit it after the space has been in use for a few weeks.
Wiring, Neutrals, and Load Ratings
Most sensors need a neutral conductor at the box to power their own electronics continuously, which is straightforward in new construction and frequently a problem in older buildings wired without one. Check the box before ordering. Sensors also carry a maximum switched load, and LED fixtures matter here in a way people underestimate: their inrush current at switch-on can be several times the running current, and a sensor sized only to the running load can fail over time. Where many fixtures share one sensor, run the sensor into a contactor and switch the load through that instead.
Sensors Alongside Other Controls
Occupancy sensing answers whether anyone is present, and complex spaces usually combine it with controls that answer other questions.
Where the space needs adjustable light level as well as automatic switching, pairing a sensor with a dimming control gives multi-level operation, and Lumera's dimmers collection covers those devices.
For a whole building where sensors, schedules, and daylight response are coordinated centrally rather than device by device, the smart controls collection covers the systems that tie it together.
Installation and Commissioning
These devices connect to building wiring and a licensed electrician should install them, confirming the neutral, the load rating against the connected fixtures, and the grounding. Beyond the wiring, budget time for commissioning: aiming the sensor, setting sensitivity, and choosing the time delay take longer than the physical installation on a multi-room job, and a sensor left at factory defaults in an unsuitable spot is the reason most disabled sensors get disabled.
Occupancy Sensor FAQs
What is the difference between an occupancy sensor and a vacancy sensor?
An occupancy sensor turns lights on automatically when someone enters and off after they leave. A vacancy sensor requires a manual press to turn lights on and only automates the off. Many energy codes specifically require manual-on operation in certain space types, so confirm the local requirement before ordering.
Should I choose PIR, ultrasonic, or dual technology?
PIR needs line of sight and catches major motion well, which suits small enclosed rooms and corridors. Ultrasonic works around obstructions and detects minor motion, which suits open offices and restrooms with stalls but can false-trigger on air movement. Dual technology combines both and is the choice for classrooms and conference rooms.
Why do my lights turn off while I am still in the room?
Usually the sensor is not detecting minor motion. A PIR sensor sees someone walk in but may miss someone sitting still at a desk, and any obstruction in its line of sight makes that worse. Either increase the time delay, reposition the sensor, or move to an ultrasonic or dual-technology unit for that space.
Why do the lights stay on in an empty room?
On an ultrasonic sensor this is nearly always air movement from an HVAC diffuser, a fan, or a door being read as occupancy. Move the sensor away from air outlets and reduce the sensitivity during commissioning. Check the time delay setting as well, since a long delay can look like a false trigger.
Do occupancy sensors need a neutral wire?
Most do, because the electronics draw power continuously even when the lights are off. Newer construction almost always has a neutral in the switch box, while older wiring frequently does not. Pull the existing device and check before ordering.
Can one sensor control several fixtures?
Yes, within its load rating, but check that rating carefully against LED loads. LED fixtures draw a brief inrush current at switch-on that can be several times their running current, and a sensor sized only to running load can fail over time. For a large group, run the sensor into a contactor and switch the load through that.
