As a device for signal acquisition and electromechanical conversion, the electromechanical technology of the sensor is quite mature. In recent years, sensor technology has developed toward miniaturization, intelligence, multi-function, and low cost. Various types of sensors such as photosensitive sensors and infrared sensors can be combined with LED lighting fixtures to form an intelligent control system. The sensor converts the collected physical quantity signals into electrical signals. The integrated signals can be used to intelligentize the collected signals through AD (analog-to-digital) converters, MCUs (microcontrollers), and DA (digital-to-analog) converters, then control LED lighting’s on and off. We can use this to set various control requirements on the MCU, control the LED light switch time, brightness, color rendering, colorful changes, so as to achieve the goal of intelligent lighting control.

Light sensor

The light-sensitive sensor is an electronic sensor that controls the automatic opening and closing of the circuit due to changes in illumination when the light is bright and dark. The light sensor can automatically control the opening and closing of the LED lighting according to the weather, time period and area. In bright daylight, by reducing its output power to reduce power consumption, compared with the use of fluorescent lights, the convenience store with an area of 200 square meters can reduce power consumption by up to 53%, and its life span is about 50,000 to 100,000 hours. Under normal circumstances, the life of LED lighting fixtures is about 40,000 hours; the color of light can also use RGB (red, green and blue) colorful changes.

Infrared sensor

The infrared sensor works by detecting infrared rays emitted by the human body. The main principle is that the infrared radiation of about 10 μm emitted by the human body is enhanced by a Fresnel filter lens and focused on a pyroelectric element PIR (passive infrared) detector. When a person moves, the emission position of infrared radiation will change, the element will lose its charge balance. Then a pyroelectric effect will release the charge, and the infrared sensor will pass through the Fresnel filter lens to change the infrared radiation energy into electrical signals, ie thermoelectric conversion. When there is no human movement in the detection area of the passive infrared detector, the infrared sensor only senses the background temperature. When the human body enters the detection area, the pyroelectric infrared sensor detects the difference between the human body temperature and the background temperature through the Fresnel lens. After the signal is collected, it is compared with the existing detection data in the system to determine whether someone is actually entering the detection area such as an infrared source.

Passive infrared sensors have three key components: Fresnel filter lenses, pyroelectric infrared sensors, and matched low-noise amplifiers. The Fresnel lens has two functions: one is focusing, which refracts the pyroelectric infrared signal onto the PIR; the other is to divide the detection area into several bright and dark areas, so that moving objects or people entering the detection area Generates a pyroelectric infrared signal on the PIR in the form of a temperature change. Generally, a low-noise amplifier is also matched. When the ambient temperature on the detector rises, especially when it is close to the normal body temperature of the human body (37°C), the sensitivity of the sensor decreases, and the gain is compensated to increase its sensitivity. The output signal can be used to drive the electronic switch to achieve the switching control of the LED lighting circuit.

Ultrasonic sensor

In recent years, ultrasonic sensors similar to the application of infrared sensors have gained more applications in automatically detecting moving objects. The ultrasonic sensor mainly uses the Doppler principle to emit high-frequency ultrasonic waves that can be perceived by the human body through a crystal oscillator. Generally, 25 ~ 40kHz wave is selected, and then the control module detects the frequency of the reflected wave. If there is object movement in the area, the frequency of the reflected wave will have a slight fluctuation, that is, the Doppler effect, so as to judge the movement of the object in the illuminated area, so as to achieve the purpose of controlling the switch.

The longitudinal oscillation characteristics of ultrasonic waves can propagate in gases, liquids and solids, and their propagation speeds are different. It also has the phenomenon of refraction and reflection. It propagates in the air at a lower frequency and decays faster, while attenuating in solids and liquid smaller and farther. Ultrasonic sensors take advantage of these characteristics of ultrasound. Ultrasonic sensors have a large sensitivity range, no visual blind spots, and no interference from obstacles. They have proven to be the most effective method for detecting small object movements. Therefore, the system can be sensitively controlled with the LED lamp. Due to the high sensitivity of the ultrasonic sensor, air vibration, ventilation, heating and cooling systems, and the movement of surrounding spaces will cause the ultrasonic sensor to trigger falsely. Therefore, the ultrasonic sensor needs to be calibrated in time.

Temperature Sensor

The temperature sensor NTC (negative temperature coefficient) is widely used for LED lamps’ over-temperature protection. If LED lamps use high-power LED light sources, multi-wing aluminum heat sinks must be used. Due to the small space of LED lamps used for indoor lighting, heat dissipation is still one of the biggest technical bottlenecks.

After the LED lamp is turned on, the heat will also accumulate to the lamp head due to the automatic rise of hot air, which affects the life of the power supply. Therefore, when designing an LED luminaire, an NTC can be closely attached to the aluminum radiator near the LED light source in order to collect the temperature of the luminaire in real time. When the temperature of the aluminum radiator of the lamp cup rises, this circuit can be used to automatically reduce the output current of the constant current source to cool down the lamp; when the temperature of the aluminum radiator of the cup rises to the limit set value, the LED power is automatically turned off to achieve the lamp Over-temperature protection, when the temperature decreases, the light will be turned on automatically.

Voice-activated sensor

A sound control sensor (microphone array) consisting of a sound control sensor, an audio amplifier, a channel selection circuit, a delay-on circuit, and a thyristor control circuit. Use the sound comparison result to determine whether to start the control circuit, and use the regulator to give the original value setting of the sound control sensor. The sound control sensor constantly compares the external sound intensity with the original value. When it exceeds the original value, it transmits a “sound” signal to the control center. The sound control sensor is widely used in corridors and public lighting places.

Microwave induction sensor

The microwave induction sensor is a moving object detector designed using the principle of the Doppler effect. It detects whether the position of the object moves in a non-contact manner, and then generates corresponding switching operations. When someone enters the induction zone and meets the lighting requirements, the induction switch is automatically turned on, the load appliance starts to work, and the delay system is started. As long as the human body does not leave the sensing area, the load appliance will continue to work. When the human body leaves the sensing area, the sensor starts to calculate the delay. When the delay ends, the sensor switch automatically turns off, and the load appliances stop working.

Read more: the basic knowledges of sensors