> Quick answer: Passive infrared (PIR) sensors detect changes in infrared radiation emitted by objects within their field of view, primarily in the 8–14 micron wavelength range [9][10]. In cold, humid air, reduced thermal contrast and atmospheric conditions can degrade performance.
In Romania’s cold, humid winters, understanding how PIR (Passive Infrared) sensors function becomes crucial for homeowners looking to secure their properties. These devices are the backbone of many solar-powered lighting systems, but their operation is influenced by environmental factors such as temperature and humidity. Let’s dive into the physical principles that govern PIR infrared detection in these conditions.
How PIR Sensors Detect Motion
Passive infrared sensors primarily detect motion by measuring changes in infrared radiation emitted by objects within their field of view [9][10]. This wavelength range is typically 8–14 microns, which corresponds to thermal radiation from human and animal bodies. The underlying physical principle is that all objects above absolute zero emit electromagnetic radiation, with the intensity and wavelength distribution governed by their temperature [2].
In cold climates, the effectiveness of PIR sensors can be reduced due to insulated clothing, which minimizes the temperature difference between a person’s body and the surrounding air [25]. This thermal insulation causes the outer surface of clothing to approximate ambient temperatures, reducing the infrared contrast necessary for detection. As a result, moving through cold, humid air may not generate enough thermal signature to trigger the sensor.
Impact of Humidity on Detection
Humidity affects PIR sensors indirectly by altering atmospheric transmission of infrared radiation [1]. Water vapor in the air absorbs infrared radiation, particularly in specific spectral bands such as 6.40–7.08 μm. This attenuation can weaken signals reaching the sensor. Although the main operational range for PIR sensors is 8–14 μm and less affected by water vapor than shorter wavelengths, high humidity may still contribute to signal degradation over longer distances or in dense fog.
Sensor Design Considerations
The design of a PIR sensor plays a critical role in its performance under varying environmental conditions. Sensors typically use a differential amplifier configuration with two or more pyroelectric detector elements wired in opposition [18]. This setup cancels out uniform changes in ambient infrared radiation, enhancing immunity to false alarms from environmental fluctuations.
Optical Components and Housing
The physical structure of the sensor housing and optical components also influences performance. PIR sensors often use a Fresnel lens made of high-density polyethylene (HDPE), which is transparent to infrared radiation [3]. However, condensation or rainy conditions can obstruct the lens, distorting or blocking the infrared signal.
Integration with Solar-Powered Lamps
The integration of PIR sensors into solar-powered lamps further complicates their operation in cold, humid environments. These systems typically include a photocell to prevent unnecessary power use during daylight [17]. The combination of low ambient light and reduced thermal contrast may result in delayed or missed detection.
Motion Detection Limitations
PIR sensors are fundamentally limited in detecting static heat sources regardless of environmental conditions [24]. A fixed heat source, including one with fluctuating intensity, does not trigger the sensor. This means that a person standing still in insulated clothing may remain undetected despite their body temperature being higher than ambient air.
Design Innovations and Alternatives
Some patents propose separating the Fresnel lens from the PIR sensor to eliminate shadow problems and allow for wider detection ranges [15]. However, this does not directly address challenges like reduced thermal contrast in cold environments. Microwave sensors are suggested as alternatives but their performance in such conditions remains unexplored.
Key Takeaways
- Thermal Contrast: Reduced contrast between moving objects and the background due to insulated clothing can degrade PIR sensor performance.
- Humidity Effects: High humidity indirectly affects detection by altering atmospheric transmission of infrared radiation, though specific impacts on 8–14 μm wavelengths are not quantified.
- Sensor Design: Differential configurations enhance immunity to false alarms but do not detect static heat sources.
Frequently Asked Questions
[
{„q”: „How does cold weather affect PIR sensor performance?”, „a”: „In cold weather, insulated clothing minimizes the temperature difference between a person’s body and surrounding air, reducing infrared contrast necessary for detection [25].”},
{„q”: „What role does humidity play in PIR sensor functionality?”, „a”: „Humidity affects PIR sensors by altering atmospheric transmission of infrared radiation; water vapor absorbs specific spectral bands like 6.40–7.08 μm, potentially weakening signals reaching the sensor [1].”},
{„q”: „Are there design improvements for PIR sensors in cold environments?”, „a”: „Patents propose separating the Fresnel lens from the PIR sensor to enhance detection range and eliminate shadow effects, though this does not address reduced thermal contrast issues directly [15].”}
]
References
- [1] Infrared_-_Wikipedia__aa7c6566 — wikipedia
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and water temperatures to protect their crops against frost or increase their catch from the sea. Even El Niño phenomena can be spotted. Using color-digitized techniques, the gray-shaded thermal images can be converted to color for easier identification of desired information. The main water vapour channel at 6.40 to 7.08 μm can be imaged by some weather satellites and shows the amount of moisture in the atmosphere. In the field of climatology, atmospheric infrared radiation is monitored to detect trends in the energy exchange between the Earth and the atmosphere. These trends provide information on long-term changes in Earth's climate. It is one of the primary parameters studied in research into global warming, together with solar radiation. A pyrgeometer is utilized in this field of research to perform continuous outdoor measurements. This is a broadband infrared radiometer with sensitivity for infrared radiation between approximately 4.5 μm and 50 μm. Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components, including mirrors, lenses and solid state digital detectors. For this reason it is classified as part of optical astronomy. To form an image, the components of an infrared telescope need to be carefully shielded from heat sources, and the detectors are chilled using liquid helium. The sensitivity of Earth-based infrared telescopes is significantly limited by water vapor in the atmosphere, which absorbs a portion of th
- [2] Passive_infrared_sensor_-_Wikipedia__6200011b — wikipedia
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# Passive infrared sensor – Wikipedia Source: Blog/Web URL: https://en.wikipedia.org/wiki/Passive_infrared_sensor Author: Date: 2005-05-31 A passive infrared sensor (PIR sensor) is an electronic device that measures infrared (IR) radiation emitted by objects in its field of view. They are most commonly used in motion detectors, including security alarms and automatic lighting systems. PIR sensors detect general movement but do not provide information on the source of motion; for that purpose, an imaging IR sensor is required. PIR sensors are often referred to simply as "PIR", or sometimes "PID" (passive infrared detector). The term "passive" indicates that the device does not emit energy, but detects infrared radiation (heat) emitted or reflected by objects. All objects with a temperature above absolute zero emit heat energy in the form of electromagnetic radiation. Usually this radiation isn't visible to the human eye because it radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose. A PIR-based motion detector is used to sense movement of people, animals, or other objects. They are commonly used in burglar alarms and automatically activated lighting systems. A PIR sensor detects changes in the amount of infrared radiation impinging upon it, which varies depending on the temperature and surface characteristics of objects in its field of view.[2] When an object, such as a person, passes in front of a background (e.g. a wall)
- [3] US10757787B2_-_LED_security_light_with_integrated_motion_sensor__9db299cf — patent
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intrusion detected by one of a plurality of PIR light bulbs pointing to different directions can trigger all PIR light bulbs to be turned on synchronously. According to the present disclosure, an LED lamp housing accommodating a Fresnel lens, a PIR motion sensor, an LED light emitting unit and a power control circuitry is configured with a two-piece housing construction divided into a first part housing and a second part housing. The first part housing serves both as a light diffuser and as a cover to protect the operating components inside the LED lamp housing. The Fresnel lens is designed to incorporate with the first part housing in two ways. The first way is to build the Fresnel lens in the light diffuser to integrate with the surface of the first part housing to collect IR ray signals generated from an intruder. The second way is to install a separate piece of Fresnel lens positioned behind the first part housing. The Fresnel lens positioned behind the first part housing can be made with a clear IR ray receptive material to avoid any shadow effect, preferably using HDPE (high density polyethylene) which performs an excellent physical reception feature to an infrared ray. Both ways can successfully collect and converge IR ray signals remotely on a focal point in a central space of the second part housing where PIR motion sensor is positioned to receive condensed IR ray signals. The second part housing accommodates all other operating components except the Fresnel lens. Th
- [9] US20040169145A1_-_PIR_motion_sensor_-_Google_Patents__fc6ec8aa — patent
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(PIR) motion sensor, which detects changes in far infrared radiation (8-14 micron wavelength) due to temperature differences between an object (e.g. a human) and its background environment. – PIR passive infrared – motion sensors Upon detection, motion sensors generally transmit an indication to a host system, which may in turn activate an intrusion “alarm”, change room lighting, open a door, or perform some other function. – One way to provide motion sensing capabilities is to provide an infrared camera. Motion in the monitored space can be tracked easily by observing the output of the camera. However, such cameras are expensive. Hence, the need for simple, relatively inexpensive PIR motion sensors, using, e.g., simple pyroelectric detectors. Because the detectors can be a significant part of the cost (5-10%) of a typical PIR motion sensor, most PIR motion sensors employ only one or two such detectors. – a typical PIR motion sensor is designed with multiple optical components (e.g. lenses or mirrors). Each component of such “compound optics” focuses the infrared radiation from objects within a respective sub-volume of the monitored space into an image appearing over the detector. – the monitored sub-volumes can be interleaved with non-monitored sub-volumes, so that a radiation producing target (e.g., a human) passing from sub-volume to sub-volume causes a “target radiation/background radiation/target radiation” pattern at the detector. In the case of humans, this pattern cau
- [10] Passive_infrared_sensor_-_Wikipedia__6200011b — wikipedia
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the PIR not be placed in such a position that an HVAC vent would blow hot or cold air onto the surface of the plastic which covers the housing's window. Although air has very low emissivity (emits very small amounts of infrared energy), the air blowing on the plastic window cover could change the plastic's temperature enough to trigger a false alarm. Sensors are also often designed to "ignore" domestic pets, such as dogs or cats, by setting a higher sensitivity threshold, or by ensuring that the floor of the room remains out of focus. Since PIR sensors have ranges of up to 10 meters (30 feet), a single detector placed near the entrance is typically all that is necessary for rooms with only a single entrance. PIR-based security systems are also viable in outdoor security and motion-sensitive lighting; one advantage is their low power draw, which allows them to be solar-powered.[6] Designs have been implemented in which a PIR circuit measures the temperature of a remote object.[7] In such a circuit, a non-differential PIR output is used. The output signal is evaluated according to a calibration for the IR spectrum of a specific type of matter to be observed. By this means, relatively accurate and precise temperature measurements may be obtained remotely. Without calibration to the type of material being observed, a PIR thermometer device is able to measure changes in IR emission which correspond directly to temperature changes, but the actual temperature values cannot be calcul
- [15] US10757787B2_-_LED_security_light_with_integrated_motion_sensor__9db299cf — patent
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second part housing accommodates all other operating components except the Fresnel lens. – the PIR motion sensor is positioned in the center space of the second part housing at the focal point to receive converged IR ray signals collected by the remotely located Fresnel lens in the first part housing space and is further surrounded by light emitting LEDs with a heat dissipating sink, the PIR motion sensor together with an IR ray signal detection circuitry is packaged with a heat insulating material to protect the PIR motion sensor and the IR ray signal detection circuitry from exposing to an unexpected high temperature environment which could affect the sensitivity of the PIR motion sensor and the IR ray signal detection circuitry. – the PIR motion sensor together with the IR ray signal detection circuitry is not much taller in construction than the surrounding LEDs, and therefore, it does not create any shadow effect. – the first part housing and the second part housing are fastened together through a connection mechanism. – the first part housing and the second part housing could be coupled and fastened by twisting a threaded construction respectively designed on the connecting edges of the first part housing and the second part housing or by using an ultrasonic welding technology. – the first part housing and the second part housing could be coupled and fastened together by screws or any similar means. – the connection mechanism can be any other method which can fasten the
- [17] US4982176A_-_Solar_powered_lighting_and_alarm_-_Google_Patents__2a7f5e5c — patent
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of the detector. – the approach or movement of the object typically changes the thermal or long wavelength radiation 52 sensed by the detector which results in an electric signal which can be amplified by amplifier 60. – the PIR sensor (detector) is preferably arranged as described in U.S. Pat. No. 3,958,118 issued to the inventor hereof with a lens system 54 which focuses the infrared rays on the detector 50. – the PIR sensor uses a minimal amount of current (power consumption of about 10 microwatts) and is designed to operate on the low voltage supplied by the rechargeable battery. Indeed, in U.S. Pat. No. – the signal output by the PIR detector 50 is amplified by amplifier 60, and fed to the light control logic and timing circuit 70. – Light control logic and timing circuit 70 preferably includes the resistance of the photocell 80 as a part of a control circuit which functions to prevent the system from turning on lamp 40 unless the dual requirements of low background light level (i.e darkness) sensed by the photocell 80, and the detection of a moving object sensed by PIR detector 50 are met. In this manner, the battery charge is maintained, as charge is not wasted by lighting lamp 40 during the daytime. – the adjustable timer 74 part of the light control logic and timing circuit 70 which is indicated as a potentiometer, but which may take any of numerous forms well known in the arts, is utilized to limit the drain on battery 30. – timer 74 closes the circuit between the b
- [18] Passive_infrared_sensor_-_Wikipedia__6200011b — wikipedia
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over distances exceeding 30 metres (100 feet). There are also designs with reversible orientation mirrors, allowing either broad coverage (around 110°) or narrow "curtain" coverage, as well as models with individually selectable segments to shape the coverage. Pairs of sensor elements may be wired as opposite inputs to a differential amplifier. In this configuration, the PIR signals cancel each other, removing the average temperature of the field of view from the output; an increase of IR energy across the entire sensor is self-cancelling and will not trigger the device. This helps reduce false detections caused by brief flashes of light or field-wide illumination (although sustained high energy exposure may still saturate the sensor). The differential arrangement also reduces common-mode interference, making the device less sensitive to nearby electric fields. However, in this configuration, the sensor cannot measure absolute temperature and is therefore used only for motion detection. When a PIR sensor is configured in a differential mode, it specifically becomes applicable as a motion detector device. In this mode, when a movement is detected within the "line of sight" of the sensor, a pair of complementary pulses[4] are processed at the output pin of the sensor. In order to implement this output signal for a practical triggering of a load such as a relay or a data logger, or an alarm, the differential signal is rectified using a bridge rectifier and fed to a transistorize
- [24] US10757787B2_-_LED_security_light_with_integrated_motion_sensor__9db299cf — patent
source passage
PIR light bulb. To remedy the loss of the adjustable feature of the detection direction, the inventor of the above related art further disclosed a technology in U.S. Pat. No. 8,123,379B2 granted Feb. 28, 2012 in which a Fresnel lens detection head is redesigned to become an eyeball construction such that the Fresnel lens detection head becomes angle adjustable. It only improves the detection capacity of the PIR light bulb to a limited extent because the fundamental issue is still the conflicting constraint of choosing an adequate dimension of the Fresnel lens between maximizing a detection scope and minimizing the shadow effect blocked by the PIR motion sensing unit positioned in the central space of the PIR light bulb. The PIR motion sensor reacts only to a moving IR source or a moving heat radiation object. A fixed heat source, even with a time variation in its intensity, does not trigger the PIR motion sensor to generate a PIR motion signal. For such reason, when the PIR motion sensor and an LED array are arranged together behind a light diffuser, the heat generated from LEDs will not affect a normal function of the PIR motion sensor in principle. Since there is no virtual need to maintain a direct touch connection between the Fresnel lens and the PIR motion sensor, it is hence feasible to knock down conventional one-piece structure of the PIR motion sensing unit into two mutually separated and remotely located components without affecting the functional performance of the
- [25] US8232909B2_-_Doppler_radar_motion_detector_for_an_outdoor__bfcc35d2 — patent
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of motion detection in an outdoor environment. More specifically, the invention relates to apparatus and methods for using Doppler radar in a motion detection application for an outdoor light fixture. Traditional motion-sensing products use passive infrared (PIR) sensors to recognize moving heat sources, such as people, animals, or car engines. PIR sensors have been the standard technology used in outdoor motion-sensing products for years, and the effectiveness of PIR sensors is typically determined by the design of the motion-sensing apparatus, the quality of the components used in making the motion sensing apparatus, and the current weather conditions. Rain, and wind-blown leaves and branches cause false positives, or false tripping, of a typical PIR motion sensor. Further, the typical PIR motion sensor performs differently in heat than it does in cold. Therefore, depending on where a user lives geographically, climate can have an effect on the performance of the PIR motion sensor and accordingly the fixture. In cold climates people are generally wearing insulated coats. The outer surface of the coat can be a similar temperature to the surrounding environment, thereby making it difficult to detect a person's motion. On the other hand, in warm climates, a person body temperature while walking across a paved driveway may be the same temperature or substantially close to the same temperature as the pavement, thereby making it difficult for the PIR sensors to detect motion. Ano
and water temperatures to protect their crops against frost or increase their catch from the sea. Even El Niño phenomena can be spotted. Using color-digitized techniques, the gray-shaded thermal images can be converted to color for easier identification of desired information. The main water vapour channel at 6.40 to 7.08 μm can be imaged by some weather satellites and shows the amount of moisture in the atmosphere. In the field of climatology, atmospheric infrared radiation is monitored to detect trends in the energy exchange between the Earth and the atmosphere. These trends provide information on long-term changes in Earth's climate. It is one of the primary parameters studied in research into global warming, together with solar radiation. A pyrgeometer is utilized in this field of research to perform continuous outdoor measurements. This is a broadband infrared radiometer with sensitivity for infrared radiation between approximately 4.5 μm and 50 μm. Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components, including mirrors, lenses and solid state digital detectors. For this reason it is classified as part of optical astronomy. To form an image, the components of an infrared telescope need to be carefully shielded from heat sources, and the detectors are chilled using liquid helium. The sensitivity of Earth-based infrared telescopes is significantly limited by water vapor in the atmosphere, which absorbs a portion of th
# Passive infrared sensor – Wikipedia Source: Blog/Web URL: https://en.wikipedia.org/wiki/Passive_infrared_sensor Author: Date: 2005-05-31 A passive infrared sensor (PIR sensor) is an electronic device that measures infrared (IR) radiation emitted by objects in its field of view. They are most commonly used in motion detectors, including security alarms and automatic lighting systems. PIR sensors detect general movement but do not provide information on the source of motion; for that purpose, an imaging IR sensor is required. PIR sensors are often referred to simply as "PIR", or sometimes "PID" (passive infrared detector). The term "passive" indicates that the device does not emit energy, but detects infrared radiation (heat) emitted or reflected by objects. All objects with a temperature above absolute zero emit heat energy in the form of electromagnetic radiation. Usually this radiation isn't visible to the human eye because it radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose. A PIR-based motion detector is used to sense movement of people, animals, or other objects. They are commonly used in burglar alarms and automatically activated lighting systems. A PIR sensor detects changes in the amount of infrared radiation impinging upon it, which varies depending on the temperature and surface characteristics of objects in its field of view.[2] When an object, such as a person, passes in front of a background (e.g. a wall)
intrusion detected by one of a plurality of PIR light bulbs pointing to different directions can trigger all PIR light bulbs to be turned on synchronously. According to the present disclosure, an LED lamp housing accommodating a Fresnel lens, a PIR motion sensor, an LED light emitting unit and a power control circuitry is configured with a two-piece housing construction divided into a first part housing and a second part housing. The first part housing serves both as a light diffuser and as a cover to protect the operating components inside the LED lamp housing. The Fresnel lens is designed to incorporate with the first part housing in two ways. The first way is to build the Fresnel lens in the light diffuser to integrate with the surface of the first part housing to collect IR ray signals generated from an intruder. The second way is to install a separate piece of Fresnel lens positioned behind the first part housing. The Fresnel lens positioned behind the first part housing can be made with a clear IR ray receptive material to avoid any shadow effect, preferably using HDPE (high density polyethylene) which performs an excellent physical reception feature to an infrared ray. Both ways can successfully collect and converge IR ray signals remotely on a focal point in a central space of the second part housing where PIR motion sensor is positioned to receive condensed IR ray signals. The second part housing accommodates all other operating components except the Fresnel lens. Th
(PIR) motion sensor, which detects changes in far infrared radiation (8-14 micron wavelength) due to temperature differences between an object (e.g. a human) and its background environment. – PIR passive infrared – motion sensors Upon detection, motion sensors generally transmit an indication to a host system, which may in turn activate an intrusion “alarm”, change room lighting, open a door, or perform some other function. – One way to provide motion sensing capabilities is to provide an infrared camera. Motion in the monitored space can be tracked easily by observing the output of the camera. However, such cameras are expensive. Hence, the need for simple, relatively inexpensive PIR motion sensors, using, e.g., simple pyroelectric detectors. Because the detectors can be a significant part of the cost (5-10%) of a typical PIR motion sensor, most PIR motion sensors employ only one or two such detectors. – a typical PIR motion sensor is designed with multiple optical components (e.g. lenses or mirrors). Each component of such “compound optics” focuses the infrared radiation from objects within a respective sub-volume of the monitored space into an image appearing over the detector. – the monitored sub-volumes can be interleaved with non-monitored sub-volumes, so that a radiation producing target (e.g., a human) passing from sub-volume to sub-volume causes a “target radiation/background radiation/target radiation” pattern at the detector. In the case of humans, this pattern cau
the PIR not be placed in such a position that an HVAC vent would blow hot or cold air onto the surface of the plastic which covers the housing's window. Although air has very low emissivity (emits very small amounts of infrared energy), the air blowing on the plastic window cover could change the plastic's temperature enough to trigger a false alarm. Sensors are also often designed to "ignore" domestic pets, such as dogs or cats, by setting a higher sensitivity threshold, or by ensuring that the floor of the room remains out of focus. Since PIR sensors have ranges of up to 10 meters (30 feet), a single detector placed near the entrance is typically all that is necessary for rooms with only a single entrance. PIR-based security systems are also viable in outdoor security and motion-sensitive lighting; one advantage is their low power draw, which allows them to be solar-powered.[6] Designs have been implemented in which a PIR circuit measures the temperature of a remote object.[7] In such a circuit, a non-differential PIR output is used. The output signal is evaluated according to a calibration for the IR spectrum of a specific type of matter to be observed. By this means, relatively accurate and precise temperature measurements may be obtained remotely. Without calibration to the type of material being observed, a PIR thermometer device is able to measure changes in IR emission which correspond directly to temperature changes, but the actual temperature values cannot be calcul
second part housing accommodates all other operating components except the Fresnel lens. – the PIR motion sensor is positioned in the center space of the second part housing at the focal point to receive converged IR ray signals collected by the remotely located Fresnel lens in the first part housing space and is further surrounded by light emitting LEDs with a heat dissipating sink, the PIR motion sensor together with an IR ray signal detection circuitry is packaged with a heat insulating material to protect the PIR motion sensor and the IR ray signal detection circuitry from exposing to an unexpected high temperature environment which could affect the sensitivity of the PIR motion sensor and the IR ray signal detection circuitry. – the PIR motion sensor together with the IR ray signal detection circuitry is not much taller in construction than the surrounding LEDs, and therefore, it does not create any shadow effect. – the first part housing and the second part housing are fastened together through a connection mechanism. – the first part housing and the second part housing could be coupled and fastened by twisting a threaded construction respectively designed on the connecting edges of the first part housing and the second part housing or by using an ultrasonic welding technology. – the first part housing and the second part housing could be coupled and fastened together by screws or any similar means. – the connection mechanism can be any other method which can fasten the
of the detector. – the approach or movement of the object typically changes the thermal or long wavelength radiation 52 sensed by the detector which results in an electric signal which can be amplified by amplifier 60. – the PIR sensor (detector) is preferably arranged as described in U.S. Pat. No. 3,958,118 issued to the inventor hereof with a lens system 54 which focuses the infrared rays on the detector 50. – the PIR sensor uses a minimal amount of current (power consumption of about 10 microwatts) and is designed to operate on the low voltage supplied by the rechargeable battery. Indeed, in U.S. Pat. No. – the signal output by the PIR detector 50 is amplified by amplifier 60, and fed to the light control logic and timing circuit 70. – Light control logic and timing circuit 70 preferably includes the resistance of the photocell 80 as a part of a control circuit which functions to prevent the system from turning on lamp 40 unless the dual requirements of low background light level (i.e darkness) sensed by the photocell 80, and the detection of a moving object sensed by PIR detector 50 are met. In this manner, the battery charge is maintained, as charge is not wasted by lighting lamp 40 during the daytime. – the adjustable timer 74 part of the light control logic and timing circuit 70 which is indicated as a potentiometer, but which may take any of numerous forms well known in the arts, is utilized to limit the drain on battery 30. – timer 74 closes the circuit between the b
over distances exceeding 30 metres (100 feet). There are also designs with reversible orientation mirrors, allowing either broad coverage (around 110°) or narrow "curtain" coverage, as well as models with individually selectable segments to shape the coverage. Pairs of sensor elements may be wired as opposite inputs to a differential amplifier. In this configuration, the PIR signals cancel each other, removing the average temperature of the field of view from the output; an increase of IR energy across the entire sensor is self-cancelling and will not trigger the device. This helps reduce false detections caused by brief flashes of light or field-wide illumination (although sustained high energy exposure may still saturate the sensor). The differential arrangement also reduces common-mode interference, making the device less sensitive to nearby electric fields. However, in this configuration, the sensor cannot measure absolute temperature and is therefore used only for motion detection. When a PIR sensor is configured in a differential mode, it specifically becomes applicable as a motion detector device. In this mode, when a movement is detected within the "line of sight" of the sensor, a pair of complementary pulses[4] are processed at the output pin of the sensor. In order to implement this output signal for a practical triggering of a load such as a relay or a data logger, or an alarm, the differential signal is rectified using a bridge rectifier and fed to a transistorize
PIR light bulb. To remedy the loss of the adjustable feature of the detection direction, the inventor of the above related art further disclosed a technology in U.S. Pat. No. 8,123,379B2 granted Feb. 28, 2012 in which a Fresnel lens detection head is redesigned to become an eyeball construction such that the Fresnel lens detection head becomes angle adjustable. It only improves the detection capacity of the PIR light bulb to a limited extent because the fundamental issue is still the conflicting constraint of choosing an adequate dimension of the Fresnel lens between maximizing a detection scope and minimizing the shadow effect blocked by the PIR motion sensing unit positioned in the central space of the PIR light bulb. The PIR motion sensor reacts only to a moving IR source or a moving heat radiation object. A fixed heat source, even with a time variation in its intensity, does not trigger the PIR motion sensor to generate a PIR motion signal. For such reason, when the PIR motion sensor and an LED array are arranged together behind a light diffuser, the heat generated from LEDs will not affect a normal function of the PIR motion sensor in principle. Since there is no virtual need to maintain a direct touch connection between the Fresnel lens and the PIR motion sensor, it is hence feasible to knock down conventional one-piece structure of the PIR motion sensing unit into two mutually separated and remotely located components without affecting the functional performance of the
of motion detection in an outdoor environment. More specifically, the invention relates to apparatus and methods for using Doppler radar in a motion detection application for an outdoor light fixture. Traditional motion-sensing products use passive infrared (PIR) sensors to recognize moving heat sources, such as people, animals, or car engines. PIR sensors have been the standard technology used in outdoor motion-sensing products for years, and the effectiveness of PIR sensors is typically determined by the design of the motion-sensing apparatus, the quality of the components used in making the motion sensing apparatus, and the current weather conditions. Rain, and wind-blown leaves and branches cause false positives, or false tripping, of a typical PIR motion sensor. Further, the typical PIR motion sensor performs differently in heat than it does in cold. Therefore, depending on where a user lives geographically, climate can have an effect on the performance of the PIR motion sensor and accordingly the fixture. In cold climates people are generally wearing insulated coats. The outer surface of the coat can be a similar temperature to the surrounding environment, thereby making it difficult to detect a person's motion. On the other hand, in warm climates, a person body temperature while walking across a paved driveway may be the same temperature or substantially close to the same temperature as the pavement, thereby making it difficult for the PIR sensors to detect motion. Ano