The science of light sensors
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Automatic lighting controls like occupancy sensors and daylight sensors can significantly reduce energy usage from lighting. Occupancy sensors use passive infrared, ultrasonic, or dual technologies to detect human presence and turn lights on or off. Ultrasonic sensors emit ultrasonic waves and detect changes in frequency to detect movement, working well in partitioned spaces. Dual sensors combine infrared and ultrasonic for higher reliability. Daylight sensors dim or switch off lights based on natural light levels. Lighting management systems allow more advanced control and settings by combining sensor technologies and scheduling. Proper sensor placement and orientation is important for coverage and avoiding nuisance switching. Occupancy sensors come in different styles and with additional features for various applications.
The science of light sensors
- 1. 727 L K - The Science of Light Sensor technology for lighting systems Jose A. Fonseca
- 2. 1. Automatic control 2. Systems on/off 3. Flow regulating systems. 4. Lighting Management Systems. 5. Planning the Layout 6. Specifying Occupancy Sensors
- 3. 1. Automatic control To eliminate energy waste, most energy codes require some way to automatically shut off lights when not in use, either based on a schedule or occupancy. Many buildings require both strategies to achieve code compliance economically and to achieve the best results with automatic shutoff. These allow the optimization of lighting installations, re- sulting in significant energy savings, subject to the levels of visual comfort needed at each location. Control systems for regulating the luminous flux more expensive; more efficient; security.
- 4. 2. Systems on/off Timers. Control of lighting circuits in a predetermined schedule. Analog or digital time switch (more expensive but allow saving the program in memory, with one or more chan- nels, allowing more than one control circuit). analog timer digital timer
- 5. Twilight Switch Allow control of lighting circuits from a given level of illuminance measured with a photodetector. Allow you to make use of natural light and should be used in conjunction with timers in situations where the work schedule does not coincide with the hours that the lighting is sufficient. This application is indicated for exteriors. BBS universal twilight switch ARGUS light-sensitive switch timer. Combines in combination with light-sensor. a light-sensitive switch and a timer.
- 6. 3. Flow regulating systems. Occupancy sensors Examples of appropriate applications include offices, class- rooms, copy rooms, restrooms, storage areas, conference rooms, warehouses, break rooms, corridors. Occupancy sensors are motion detectors. A motion detector is an electronic device that detects the physical movement in a given area and transforms mo- tion into an electric signal. These sensors turn on lighting in environments occupied and after a pre-set duration turn off lighting in unoccupied environments. Technologies: • Passive InfraRed (PIR). • Ultrasonic. • Dual-technology. • Radar-based. • Daylight sensors.
- 7. Passive Infrared Motion Detector PIR respond to the infrared heat energy emitted by people. Passive means they detect radiation, do not emit it. The sensor is able to recognize a thermal infrared image (created by infrared technology combined with a heat sensor). Sensitive to objects that emit 10 micrometers radiation wave- length around the same value as the wavelength of heat emitted by the human body. Dual PIR Sensor Coverage Area
- 8. Single PIR Sensor Coverage Area Sensitivity decreases with re- moteness; movement of hands is sensed at 3.5 meters, the move- ment of the arm and torso to 7 meters and movement of the body up to 14 meters. Directly replaces the wall or ceiling switch and are most suit- able for small environments. Issues that might complicate their application: low levels of motion by occupants, obstacles blocking the sensor’s view; sensors mounted on sources of vibration or within 6-8 feet of air diffusers.
- 9. Ultrasonic Sensor Activates a quartz crystal which emits utltra-sonic waves at frequencies above the limits of human perception (25 to 45kHz), by means of space, to detect the presence of occupants. This high frequency signal is compared with the frequency of the reflected signal (Doppler effect) and any difference is interpreted as the presence of someone within coverage.
- 10. Ultrasonic sensors, meanwhile, are highly suitable for spaces in which a line of sight is not possible, such as par- titioned spaces, restrooms, open offices, enclosed hallways and stairways. Issues that might complicate their application include: ceilings higher than 14 feet; high levels of vibration or air flow, open spaces that require selective coverage, such as control of individual warehouse aisles. Experts in the field of optics have developed different designs or patterns, each of which is protected by its own patent, to provide different coverage capabilities.
- 11. Dual-Technology Sensors Sensor that uses both technologies, infrared and ultrasound. In this case, the lighting system is activated only when both detect the presence of people, which increases system reliability by preventing the lighting system to light up unnecessarily. Because of higher cost, applications are indicated for environments where you need a high degree of detection, such as in classrooms and conference rooms.
- 12. Radar based Continuous Wave (CW) motion detectors use microwave signals to emit frequencies to bounce off of the surround- ing area (which is why they are sometimes referred to as “microwave motion detectors”) . Microwave sensors, which work much like ultrasound with detection of noise, they emit receive and compare frequency changes (when intruder passes field of sensor). CW motion detectors are gen- erally more expensive than PIR motion detectors. This is because they are highly sensitive, and are very reliable over longer distances. Suitable for industrial environments.
- 13. Daylight sensors and flow regulators “dimming” Levels from natural lighting luminance are detected by a photocell that adjusts and controls the flow of artificial light depending on this level so as to have luminance lev- el desired. The artificial lighting is switched off continuously as nat- ural light levels increase. This procedure avoids the prob- lems of the system on/off. Adjustment to 1% of artificial Adjustment to 100% of arti- illumination levels. ficial illumination levels.
- 14. 5. Lighting Management Systems Systems such as DALI (Digital Addressable Lighting Interface) and EIB (European Installation Bus) Allow combination of technologies: • Adjusting the lighting for the amount of natural light • Control sensors and scheduling of movement with advantage of the user choosing the control method. • Possibility of creating and memorizing scenarios, ie, possibility to adapt the lighting to local conduct. This technology can be used in large office buildings such as schools, hospitals, commercial buildings but also in in- dustrial and residential buildings.
- 15. Advantages: • Flexible solutions system; • Rapid amortization of investment; • Variety of Settings; • Energy management, maintenance of light sources; • integration of the lighting system; • Expandability; • Attractive design; Disadvantages: • High initial investment; • Separation of the power circuit and command, more connections, more cabling.
- 16. 5. Planning the Layout Proper sensor location minimizes the possibility of nuisance switching and ensures lights will turn on when a person enters the space and the sensor will maintain an unob- structed line of sight to task areas at all times. Specify the orientation of the sensor. Sensors should point toward the area of greatest activity in the space. Must also determine whether to install the sensor at the wall switch, wall, corner, ceiling or task.
- 17. Ceiling-mounted sensors are appropriate for large areas featuring obstacles, such as partitions, as well as narrow spaces, such as corridors and warehouse aisles. Sensors mounted high on a wall and at corners are appropriate for covering large areas that feature obstacles. Wall-switch or wall-box sensors are relatively inexpensive and easy to install, and they are appropriate for smaller, enclosed spaces, such as private offices with clear lines of sight between the sensor and the task area. Workstation sensors are appropriate for individual cubicles. Multi Lens for coverage of up to360º
- 18. 6. Specifying Occupancy Sensors • line-voltage operation without a power pack, in enclosed spaces or where junction boxes are of difficult access. • self-calibrating sensors adapt to space-use patterns • manual-on operation for greater energy savings • power packs with two relays for bi-level switching • an integral photosensor to keep lights off if it detects sufficient daylight • a combination dimmer- occupancy sensor • isolated relay for inter- facing with other loads, such as HVAC • digital-network connec- tivity • small sensors available as part of the light fixture.