PIR Motion Sensors & Switches

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Introduction: Lighting controls play a critical role in electric lighting systems, providing the function of:

  • • Turning the lights on and off using a switch; and/or

  • • Adjusting light output up and down using a dimmer

In recent decades, technological development has increasingly automated these functions and allowed integration of devices into larger, more flexible systems. The result is significantly expanding energy-saving opportunities, flexibility, reliability and interoperability between devices from different manufacturers.

The Lighting Control System: Lighting control systems contain three components linked by communication wiring, which is used to transmit control signals, and power wiring, which supplies power.


Sensing Device

Logic Circuit

Power Controller


Provides information to logic circuit

Decides whether to supply lighting, and how much

Changes the output of the lighting system

We can therefore view a lighting control system or device as an apparatus that 1) receives information, 2) decides what to do with that information, and 3) changes the operation of the lighting system. In other words, we can look at lighting control devices based on inputs and outputs. Below are three examples.

Control Input Decision-making Output

Occupancy sensor

Sensor detects presence or absence or people

Decide whether to turn on or shut off lights

Sends signal to relay, which closes or opens circuit

Control station and dimming panel

User presses button to recall preset scene

Control station recalls scene from memory and sends signal to dimmer at dimming panel

Dimmer adjusts light output to desired level

Dimmable ballast

Controller provides signal to dim

Ballast is instructed to dim, and by how much

Ballast alters the current to the lamps, dimming them

Below is an example of a robust lighting control system with a control station, occupancy sensor, photosensors and time switch or centralized switching system providing a variety of inputs to the master lighting controller. The lighting controller can be a switching panel, dimming panel or both linked together. The controller in turn controls the lighting load with a variety of outputs based on decisions made by the logic circuits. Since different control strategies may have overlapping device requirements, control synergies can be gained by building a system of simple components.

Lighting Control System

Purpose of Lighting Controls: In many applications, the overall purpose of the lighting control system is to eliminate waste while providing a productive visual environment. This entails:

  • Providing the right amount of light
  • Providing that light where it’s needed
  • Providing that light when it’s needed

The Right Amount of Light … Control systems provide the right amount of light. This lighting decision is based on the type of tasks being performed in the space. Lighting controls support this goal in two ways.

Lighting controls provide flexibility in adapting the lighting system to different uses. For example, a school auditorium, which is home to a diverse range of activities, would need different light levels for these activities.

Lighting controls provide the ability for users to adjust light levels based on changing needs or individual preference, either through dimming or through bi- or multi-level switching. Dimming provides the greatest amount of flexibility in light level adjustment.

By enabling the lighting system to deliver the right amount of light to the task, the control system can eliminate energy waste while providing a productive visual environment.

… Where It’s Needed … Lighting controls support the lighting system putting light where it’s needed. This entails establishing control zones, which is a light fixture or group of fixtures controlled simultaneously as a single entity by a single controller. Zones are typically established based on types of tasks to be lighted, lighting schedules, types of lighting systems, architectural finishes/furnishings, and daylight availability.

The greater the resolution of the control zones—that is, the smaller they are—the greater the precision the control system can provide. For example, a control system can turn the lights on automatically when a person enters a building during non-operating hours. Only the areas to be used should be lighted, however, and not the entire floor. A zone can also be as small as single ballast or light fixture, which enables the greatest amount of control resolution. For example, each user in an open office can be given capability via PC or handheld remote to dim his or her own lighting to personal preference.

Generally, the smaller the control zone, the greater the control resolution and potential utility cost savings and the greater the opportunity to enable the lighting system to support visual needs.

… And When It’s Needed: An effective control system ensures that the lighting system operates—and consumes energy which costs the owner money—only when it’s needed. Determining when the lighting system should be operating depends on how the space is occupied. This will entail whether a time-based or a threshold event should be the deciding factor in whether the lights should be turned on or shut off.

If occupancy is predictable, a time-based strategy can be considered. For example, a switching system can be scheduled to automatically shut off the lights by area, by floor or in an entire building if a building’s occupancy is predictable.

If occupancy is not predictable, a threshold-event-based strategy can be considered. For example, occupancy sensors can be used to automatically turn on and shut off lights in areas depending on whether the sensor detects the presence or absence of people in the monitored area.

By ensuring the lighting system provides light only when it’s needed, the control system can significantly reduce wasted energy and generate utility cost savings for the owner.

Energy Management: Advanced lighting control devices and systems can be used to reduce ongoing costs for the owner and thereby increase profitability and competitiveness. According to the New Buildings Institute, lighting controls can reduce lighting energy consumption by 50% in existing buildings and by at least 35% in new construction.

  • Lighting energy: Controls can reduce the amount of power drawn by the lighting system during operation and also the number of operating hours, thereby reducing utility energy charges.
  • Lighting demand: Controls can reduce the amount of power drawn by the lighting system, reducing utility demand charges—particularly during peak demand periods, when demand charges are highest.

These cost savings can produce a short payback and a high rate of return for the investment in the new controls. In new construction, the rate of return is often higher because only the premium, not the total installed cost, will be recouped before positive cash flow is realized.

Visual Needs:The project may be driven by business benefits other than energy savings by providing increased performance and flexibility:

  • • Adapt the lighting for multiple uses of a space, such as a conference room or gymnasium.

  • • Adapt the lighting to evolving space needs resulting from employee churn and office strategies such as hoteling and hot-desking.

  • • Mood-setting for restaurants and similar applications.

  • • Increasing worker satisfaction by providing personal control of their lighting systems in office and other environments.

  • • Enhanced aesthetics and image, greater space marketability, and pollution prevention.

Switching or Dimming? The first primary decision after defining the load and the application goals is whether to switch or dim the load. Switching and dimming are stand-alone strategies but are often used in the same facility, and may be integrated in the same control system.

What Degree of Automation Is Required? Manual lighting controls range from a single switch to a bank of switches and dimmers that are actuated by toggles, rotary knobs, push buttons, remote control, and other means. Manual controls can be cost-effective options for small-scale situations. However, as the size of the lighting system grows, manual controls lose their cost-effectiveness. In addition, manual controls often waste energy because the decision to shut off the lights when they are not needed is based entirely on human initiative.

Method Strategy Manual vs. Automatic


Occupancy sensors

Turn the lights on or off automatically based on whether space is occupied

Scheduled automatic shut-off at end of workday switching panels, time-clocks or building automation system

Turn selected lights on or off automatically based on schedule when space is predictably unoccupied

Scheduled automatic shut-off of select loads (bi-level switching) during peak demand periods, time-clocks or building automation system

Turn off one or two lamps in each fixture or checkerboard fixtures automatically for load shedding during peak demand periods

Bi-level switching using wall switches controlling lighting system layered as two separate circuits

Turn selected circuit on and off manually to achieve ON, 50% light level, and OFF

Multilevel switching using photosensors and low-voltage relay

Turn the lights off automatically based on available ambient daylight


Dimming control of smaller loads using wall-box and remote dimmers

Adjust light output manually based on space need or personal preference

Dimming control of larger loads using control stations and dimming panels

Adjust light output manually based on space need or personal preference

Daylight harvesting using photosensors, controller and dimmable ballast

Adjust light output automatically to maintain target light level as daylight enters space

Adaptive compensation using dimming panels and scheduling device such as time-clock

Adjust light output automatically to provide lower light levels at night based on studies about human lighting preferences

Peak shaving and load shedding using dimming panels and scheduling or control device

Adjust light output automatically during peak demand periods and/or manually based on utility request to curtail load

Example Strategies:
Below are six sample strategies defined according to whether they are dimming or switching, local or centralized, and manual or automatic.

What Degree of Control Accuracy Is Required? A key step in designing a lighting control system is to determine the degree of control over the lighting system, which means breaking the load up into zones. A control zone is a fixture or group of fixtures controlled simultaneously as a single entity by a single controller. Zones are typically established based on types of tasks to be lighted, lighting schedules, types of lighting systems, architectural finishes/furnishings and daylight availability. Establishing smaller zones increases control accuracy and flexibility but also increases cost.

1. Introduction

The rooms where lamps are unnecessarily left switched on for long periods of the day are typically the:

  • • Drying rooms

  • • Changing rooms

  • • Canteen

  • • Toilets

  • • Office kitchen

  • • Meeting rooms

Occupancy sensors should be installed in these areas in order to assure that the light is switched of during periods where the space is not occupied.

2. Working Principle

 Occupancy sensors serve three basic functions:

  • • To automatically turn lights on when a room becomes occupied,

  • • To keep the lights on without interruption while the controlled space is occupied, and

  • • To turn the lights off within a preset time period after the space has been vacated.

• The system consists of a motion detector, an electronic control unit, and a controllable switch (relay).

Occupant sensor control system (3) 

In most occupant sensor systems, the motion detector and controller are housed in one package. The power supply and relay comprise another integral unit. In wall box-type sensors, components are integrated into one compact package, designed to fit into an existing switch box.
Occupant sensors can also be connected to low-voltage relay and building automation systems.

3. Sensor Types

There are 3 types of occupancy sensors available:

Passive Infra Red Sensors

Passive infrared sensors (PIR) are triggered by the movement of a heat-emitting body through their field of view. PIR sensors cannot "see" through opaque walls, partitions, or windows so occupants must be in direct line-of-site of the sensor.

Ultrasonic sensors

Ultrasonic sensors emit an inaudible sound pattern that is disrupted by any moving object altering the signal returning to the sensor (Doppler shift). They are best suited for spaces where line-of-sight view to the occupant is not always available. This type of sensor detects very minor motion better than most infrared sensors.

Dual-technology occupancy sensors

Dual technology occupancy sensors use both passive infrared and ultrasonic technologies for less risk of false triggering (lights coming on when the space is unoccupied). Combining the technologies requires a more reliable, yet slightly larger and more expensive device.

We suggest for installation of occupancy sensors in construction villages, the use of PIR sensors is sufficient, as a detection of minor motions only would lead to unnecessarily switching of lights.
Most PIR sensors are sensitive to hand movement up to a distance of about 3m, arm and upper torso movement up to 6m and full body movement up to 12m. [1] 

4. Sensor Setting

PIR sensors can be reset as required. [2]

SENS -- sensitivity sets how far away and how small a movement will trigger the light.

TIME -- the length of time the light remains on after the last detected movement

Passive infra-red sensors used in toilets, changing rooms, drying rooms and office kitchen can be set to provide at least 5 minutes of light once activated. In canteen and meeting rooms lights should probably remain on longer after a detected movement.

5. Sensor Installation

Passive infra-red sensors could be retro-fitted to the existing lights or mounted to the wall.
Wall-box type PIR occupancy sensors are easy to install. These are best suited for small, enclosed spaces where the sensor replaces the light switch on the wall and no extra wiring is required. In the case of the construction village under investigation these would be best suited for the use in all toilets, meeting rooms and office kitchens.

Wall mounted PIR sensor

Occupancy sensor placement is very important to the successful implementation of the control design intent. The layout of space has to be considered by selecting and mounting an occupancy sensor. The optimum mounting location will depend on the shape of the room, the expected location of occupants and potential obstacles such as the lockers in the drying room.
We, therefore, recommend the installation of ceiling mounted sensors in canteen, changing and drying rooms.

Occupancy sensors must be located to ensure that they will not detect movement outside of the desired coverage area, through an open doorway, for example.

6. Energy Savings

The following energy savings can be realized using occupancy sensors:



Private Office

15 – 50%


40 – 50%

Conference Room

25 – 70%


32 – 92%


32 – 84%

Storage Areas

50 – 80%


Typical values of energy savings for various occupancy areas [1]

Using PIR sensors for intermittent occupied areas of the construction village it is estimated that lights are switched off:

At least 80% of the time in toilets, drying room, changing rooms and office kitchen.

At least 65% of the time in canteen and meeting rooms

These estimations take into account the occupancy pattern of the different areas studied at the construction site we have visited. 

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