Lighting represents a significant portion of energy costs in most buildings, surpassed only by HVAC equipment. However, lighting energy consumption can be reduced by upgrading to high-efficiency LED bulbs , or by deploying control systems that only keep lights on when needed. Occupancy sensors provide a simple way to automate lighting, achieving quick savings.
In simple terms, occupancy sensors automatically turn lights on when human presence is detected and turn them off when the covered area is empty. Occupancy sensors should not be confused with vacancy sensors, which also turn off lights automatically but require them to be activated manually.
There are three main types of occupancy sensors. Each option has pros and cons, and the best choice is determined by the application in question:
- Passive Infrared (PIR)
- Ultrasonic
- Dual technology
Make your building's lighting systems smarter and more efficient.
Passive infrared sensors
PIR sensors are based on heat detection: the body temperature of humans is higher than the temperature of internal surfaces and objects. These sensors perceive humans as warm moving objects against a cooler background and can control the lighting system accordingly.
Unless a kitchen appliance or a domestic hot water system is used within the range of PIR sensors, humans are the most common sources of heat. Therefore, these sensors have a low chance of false activation. However, many design considerations should not be forgotten:
- PIR sensors require a direct line of sight between themselves and occupants to detect heat. They are not recommended in applications where obstacles may block your field of vision, such as office areas with multiple cubicles.
- Infrared sensors have multiple blind spots, which means they cannot provide full 360° coverage of your surroundings. This limits its use in applications where occupants don't move much – someone sitting in a blind spot won't trigger the sensor.
- PIR sensors should not be installed near HVAC vents where air is supplied at a higher or lower temperature than indoor spaces, depending on the season. These air temperature differences can make occupancy detection difficult.
Ultrasonic Sensors
Ultrasonic sensors use similar principles to underwater sonar and bat echolocation. They emit a high-frequency sound that is reflected off surfaces and indoor objects, and the sound pattern remains constant when there is no movement. Normal sound patterns are disrupted when a person enters the ultrasonic sensor's coverage area, allowing detection, and this applies even to someone standing still.
The main advantage of ultrasonic sensors is their ability to detect occupants behind obstacles. Unlike PIR sensors, they can pick up smaller movements. However, ultrasonic sensors also have their limitations:
- Its high sensitivity increases the possibility of false ignition, turning on the lights in response to sounds or movements that are not caused by the occupants.
- They cannot provide isolated coverage. For example, if you use an ultrasonic sensor to control lights in a warehouse aisle, they will likely also respond to movement in adjacent aisles (only a PIR sensor is effective here).
- As you can imagine, an ultrasonic sensor is ineffective when installed near HVAC equipment or other vibrating machines.
Dual Technology Sensors
As the name implies, these sensors have infrared and ultrasonic detection. They only activate the lamps when both inputs are present and only turn them off when both inputs disappear. This provides very accurate occupancy detection, significantly reducing the chance of a false on or false off.
Dual technology sensors tend to have a higher cost, having two separate detection systems. They are intended for applications that require high precision, such as classrooms or conference rooms. Otherwise, PIR and ultrasonic sensors are recommended – whichever is best suited to the application.
Final Recommendations
When lighting is controlled with occupancy sensors, savings of over 10% are common, with a payback period of less than a year in many cases. However, it is important to choose the right sensors for each application and place them where they achieve optimal coverage. Also consider that some lighting systems have a fixed operating schedule and time-based controls are a better option in these cases.
Occupancy sensors can be combined with dimmers and daylight responsive controls to further increase the efficiency of lighting systems. If this is complemented with an LED lighting upgrade, savings of over 80% are achievable.
