Lighting Control Sensor Technologies
PIR (PASSIVE INFRARED) TECHNOLOGY
PIR (passive infrared) sensors measure the infrared light that is radiated by, or reflected from people and objects. In an unoccupied room, the PIR sensor will measure the infrared radiation from the floor, furniture and walls (the background).
When someone moves in front of this background, the temperature at a point in the sensor's field of view will rise from room temperature to body temperature, and then back again (as the person moves away). This change in incoming infrared radiation triggers the detection.
PIR sensors are called ‘passive' because they do not transmit any probe signal for measurement. PIR sensors detect motion based on the infrared light they receive and measure. This means their power consumption is very low. This is important when using sensors as part of a DALI lighting control system: in general, the lower the power consumption of the devices on a DALI system, the fewer subnets are required.
Microwave and ultrasonic sensors are ‘active’ because they continuously transmit energy and analyse the signal reflected back to detect motion.
MOTION, NOT TEMPERATURE — WHY DOESN'T A PIR SENSOR REACT TO A PERSON SITTING STILL IN A ROOM?
A PIR sensor reacts to detected movement, and not just to detected temperatures.
This can mean that when you are sitting still at your desk alone in your office, that the lights will dim down. You will have to move a little so that the lights go up again.
If the lights dim too often or too quickly when you are in a room, the sensor's time-out setting may be too short: ask your facilities manager to adjust the lighting control system timings.
HOW CAN A PIR SENSOR "KNOW" IF SOMEONE IS MOVING, BUT NOT REACT WHEN SOMEONE IS JUST SITTING STILL?
Inside all PIR sensors there are two or more sensing elements. When a body moves in front of the sensor, it creates changing temperature differential between the elements. When the temperature difference between elements changes, an electrical signal is induced. This means that the PIR sensor reacts to movement, rather than to temperature.
This means that the PIR sensor should not be triggered by changes in sunlight, or temperature changes in the room. If you leave a hot drink in an unoccupied room, it will not activate the lights as the drink cools: the PIR senses movement, not the temperature of still objects.
PIR sensors should not be installed in the path of a light source, nor where they can be lit by direct sunlight.
Helvar PIR sensors: PRODUCT PAGES
Microwave sensors are useful for detecting motion in large and unusually shaped areas. They are generally more sensitive to detection of movement than PIR sensors, and can cover larger areas from single observation point.
Microwave sensors are 'active': they emit a continuous wave of microwave radiation, and analyse the reflected signal for any changes caused by people or objects moving towards or away from the sensor. Microwave-based lighting control sensors generally consume more energy than PIR sensors, which should be considered when designing a DALI system.
MICROWAVES CAN GO THROUGH WALLS AND WINDOWS
Microwaves can travel through thin walls, partitions and glass. This can be an advantage if you need to detect motion in a space with glass partitions, for example. This sensitivity can be a disadvantage, because it means that motion outside a room could trigger the lights in a room, if presence detection is used and the microwave sensor is not correctly located.
Metal surfaces reflect microwaves, so microwave sensors may not be suitable for areas with large metal surfaces, such as data centres or warehouses with metal racks.
MICROWAVE FREQUENCIES: LOCAL AND NATIONAL REGULATIONS
Different microwave frequencies are permitted in different geographical locations. A microwave-based product for use in France, Portugal and Switzerland may not be allowed in many parts of Asia, or the UK and certain other European countries, for example. With our international network of offices and partners, Helvar can advise you on the relevant standards.
Helvar microwave sensors: PRODUCT PAGES
LIGHTING CONTROL WITH LIGHT SENSORS
Daylight harvesting is the general term for making optimum use of natural daylight that comes into a room or area. In the context of lighting control, this is usually by automatically adjusting electric light levels in response to changes in ambient light. By making the most of natural daylight, effective daylight harvesting helps provide comfortable and energising spaces for people to be in, as well as reducing energy consumption.
When using light level sensors to control a room's lighting, you need to decide whether to, either measure just the level of ambient light (daylight), OR to measure a combination of ambient light and the electric light which is being controlled.
When considering lighting control sensors, ambient light refers to the daylight coming into a room. A room with large windows may have high levels of ambient light in summer daytime.
When considering lighting control sensors, available light is the combination of ambient light and electric lights in a room or space. A lighting control system in a classroom or office will probably be used to maintain particular levels of available light, possibly by adjusting the electric lights as ambient light changes.
Helvar lighting control systems have a 'constant light' feature which maintains a set level of available light, by adjusting the electric lighting in a room to compensate for changes in ambient light. In schools and offices, for example, students or office workers can continue their working day without the disruption of noticing the electric light levels changing.
LIGHT LEVEL SENSING AND PHOTOCELLS
Helvar's multisensors have PIR occupancy sensors and photocells, for measuring available light in a particular location. Helvar's DALI External sensor also uses photocells to measure light levels outside buildings. Based on the level of light detected by the photocells, sensors can adjust the lighting levels.
CONSTANT LIGHT WITH OCCUPANCY DETECTION AND MANUAL CONTROL
Constant light does not mean that the lights must always be on. In a sunny reception area, for example, you may want to have lights come on when someone comes in, and, as the ambient light changes throughout the day, adjust the level of electric light, so that the room is not too bright and is comfortably lit for people using the space.
OPEN LOOP: SENSES AMBIENT LIGHT ONLY
An open loop system measures the ambient light only, and is often used where the electric light needs to be adjusted automatically depending on daylight levels, but where achieving a very specific target light level is not important. The light sensor is either outside, measuring daylight directly, or inside, measuring the ambient light in an area with a large amount of daylight coming in.
The sensor can be used to adjust the electric lighting depending on the ambient light levels. This is useful, for example, if you want a glass walkway's lights off when there is a certain amount of external light, or if you want an entrance hall to be lit in the morning if it is still dark outside.
This is called 'open loop' because the electric lights do not affect the light sensor reading.
CLOSED LOOP CONTROL: SENSES AMBIENT LIGHT AND THE ELECTRIC LIGHT WHICH IT CONTROLS
Closed loop systems measure the available light, which is a combination of ambient light and the electric light which is being controlled. Closed loop control is usually used in classrooms, small offices and other places where a particular light level in a single zone (rather than zones with different levels of light) is required.
The light sensor 'sees' the electric light which it controls, and because the sensor is receiving this feedback on its control performance, it is called a closed loop system.
The target light level can be fixed by a commissioning engineer or can be directly set by a user using buttons on a wall panel. The system compares the target level and the measured light level, and adjusts light output accordingly. This continuous process maintains the target light level in the room.
Helvar products with a light sensor: PRODUCT PAGES