727 L K - The Science of LightSensor technology for lighting systems Jose A. Fonseca
1. Automatic control2. Systems on/off3. Flow regulating systems.4. Lighting Management Systems.5. Planning the Layout6. Specifying Occupancy Sensors
1. Automatic controlTo eliminate energy waste, most energy codes requiresome way to automatically shut off lights when not inuse, either based on a schedule or occupancy.Many buildings require both strategies to achieve codecompliance economically and to achieve the best resultswith automatic shutoff.These allow the optimization of lighting installations, re-sulting in significant energy savings, subject to the levelsof visual comfort needed at each location.Control systems for regulating the luminous fluxmore expensive;more efficient;security.
2. Systems on/offTimers.Control of lighting circuits in a predetermined schedule.Analog or digital time switch (more expensive but allowsaving the program in memory, with one or more chan-nels, allowing more than one control circuit). analog timer digital timer
Twilight SwitchAllow control of lighting circuits from a given level ofilluminance measured with a photodetector.Allow you to make use of natural light and should be usedin conjunction with timers in situations where the workschedule does not coincide with the hours that the lightingis sufficient. This application is indicated for exteriors.BBS universal twilight switch ARGUS light-sensitive switch timer. Combinesin combination with light-sensor. a light-sensitive switch and a timer.
3. Flow regulating systems. Occupancy sensorsExamples of appropriate applications include offices, class-rooms, copy rooms, restrooms, storage areas, conferencerooms, warehouses, break rooms, corridors.Occupancy sensors are motion detectors.A motion detector is an electronic device that detects thephysical movement in a given area and transforms mo-tion into an electric signal.These sensors turn on lighting in environmentsoccupied and after a pre-set duration turn off lighting inunoccupied environments.Technologies: • Passive InfraRed (PIR). • Ultrasonic. • Dual-technology. • Radar-based. • Daylight sensors.
Passive Infrared Motion DetectorPIR 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 heatsensor).Sensitive to objects that emit 10micrometers radiation wave-length around the same value asthe wavelength of heat emittedby the human body. Dual PIR Sensor Coverage Area
Single PIR Sensor Coverage AreaSensitivity decreases with re-moteness; movement of hands issensed at 3.5 meters, the move-ment of the arm and torso to 7meters and movement of thebody up to 14 meters.Directly replaces the wall orceiling switch and are most suit-able for small environments.Issues that might complicatetheir application:low levels of motion byoccupants, obstacles blockingthe sensor’s view;sensors mounted on sources ofvibration or within 6-8 feet ofair diffusers.
Ultrasonic SensorActivates a quartz crystal which emits utltra-sonic wavesat frequencies above the limits of human perception (25to 45kHz), by means of space, to detect the presence ofoccupants.This high frequency signal is compared with the frequencyof the reflected signal (Doppler effect) and any differenceis interpreted as the presence of someone within coverage.
Ultrasonic sensors, meanwhile, are highly suitable forspaces in which a line of sight is not possible, such as par-titioned spaces, restrooms, open offices, enclosed hallwaysand stairways.Issues that might complicate their application include:ceilings higher than 14 feet; high levels of vibration or airflow, open spaces that require selective coverage, such ascontrol 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.
Dual-Technology SensorsSensor that uses both technologies, infrared and ultrasound.In this case, the lighting system is activated only whenboth detect the presence of people, which increases systemreliability by preventing the lighting system to light upunnecessarily.Because of higher cost, applications are indicated forenvironments where you need a high degree of detection,such as in classrooms and conference rooms.
Radar basedContinuous Wave (CW) motion detectors use microwavesignals 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 ultrasoundwith detection of noise, they emit receive and comparefrequency changes (when intruder passes field of sensor).CW motion detectors are gen-erally more expensive thanPIR motion detectors. Thisis because they are highlysensitive, and are veryreliable over longer distances.Suitable for industrialenvironments.
Daylight sensors and flow regulators “dimming”Levels from natural lighting luminance are detected bya photocell that adjusts and controls the flow of artificiallight 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.
5. Lighting Management SystemsSystems such as DALI (Digital Addressable LightingInterface) 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 suchas schools, hospitals, commercial buildings but also in in-dustrial and residential buildings.
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.
5. Planning the LayoutProper sensor location minimizes the possibility of nuisanceswitching and ensures lights will turn on when a personenters 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 shouldpoint toward the area of greatest activity in the space.Must also determine whether to install the sensor at thewall switch, wall, corner, ceiling or task.
Ceiling-mounted sensors are appropriate for large areasfeaturing obstacles, such as partitions, as well as narrowspaces, such as corridors and warehouse aisles. Sensorsmounted high on a wall and at corners are appropriatefor covering large areas that feature obstacles.Wall-switch or wall-box sensors are relatively inexpensiveand easy to install, and they are appropriate for smaller,enclosed spaces, such as private offices with clear lines ofsight between the sensor and the task area. Workstationsensors are appropriate for individual cubicles. Multi Lens for coverage of up to360º
6. Specifying Occupancy Sensors• line-voltage operation without a power pack, in enclosedspaces 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 detectssufficient daylight• a combination dimmer-occupancy sensor• isolated relay for inter-facing with other loads,such as HVAC• digital-network connec-tivity• small sensors availableas part of the light fixture.