LED Light and Sensor Technology

Combination of photosensitive sensor and LED lamp

Wind and solar LED street lights are highly intelligent and unattended road lighting fixtures that use wind and sunlight to generate electricity and use batteries to store energy. Therefore, automatic energy management is very important. Photosensitive sensors are ideal electronic sensors that can control the automatic switching of circuits due to changes in illumination during daylight and darkness (sunrise and sunset). Figure 2 shows the appearance of a photosensitive sensor. Figure 3 is a photosensitive resistor board of a photosensitive sensor, which is very sensitive to the brightness of light. Figure 4 is a basic principle diagram of photoelectric conversion.

The photosensitive sensor can automatically control the opening and closing of the mall's LED lighting fixtures according to the weather, time period and region. In bright daytime, the power consumption is reduced by reducing its output power. Compared with the use of fluorescent lamps, a convenience store with a store area of ​​200m2 can reduce the power consumption by up to 53%. The life span is also up to about 50,000-100,000 hours. Generally speaking, the life span of LED lighting fixtures is about 40,000 hours; the color of the light can also be changed in RGB to make the mall lighting more colorful and the atmosphere more lively; compared with the original blue LED with $ phosphor, the purple LED with red, green and blue phosphor has a higher color rendering.

Infrared sensor and LED lamp combination

Infrared sensors work by detecting infrared rays emitted by the human body. The main principle is: the infrared rays of about 10um emitted by the human body are enhanced by the Fresnel filter lens and then transmitted to the pyroelectric element PIR. When a person moves, the emission position of the infrared radiation will change, and the element will lose its charge balance, and the pyroelectric effect will occur to release the charge outward. The infrared sensor (PIR) converts the change of infrared radiation energy passing through the Fresnel filter lens into an electrical signal, that is, 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 a human body enters the detection area, the pyroelectric infrared sensor senses 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 there is really someone or other infrared source entering the detection area.

Passive infrared sensors have three key components: Fresnel filter lens, pyroelectric infrared sensor (PIR) and matching low noise amplifier. Fresnel lens has two functions: one is focusing, that is, refracting the pyroelectric infrared signal on the PIR; the other is to divide the detection area into several bright and dark areas, so that the moving objects (people) entering the detection area can produce changing pyroelectric infrared signals on the PIR in the form of temperature changes. 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 through it to increase its sensitivity. The output signal can be used to drive the electronic switch to realize the switch control of the LED lighting circuit. Figure 5 is the appearance of the infrared sensor, and Figure 6 is the internal structure and internal circuit diagram of the infrared sensor. Figure 7 shows an LED lighting fixture with an infrared sensor. This is an E27 standard screw-type lamp. Its power supply range is AC180V-250V (50/60Hz). The infrared sensor detection range is about 3M-15M. Its standard product IFS-Bulb 3W lamp reaches 80 lm, and 5W lamp reaches 140 lm. An infrared sensor is embedded in the central part of the LED light source module. Once the infrared sensor detects a person's body temperature, the LED bulb will automatically turn on and off within 50 seconds. It is suitable for any indoor application, such as corridors, storage rooms, stairs and hall entrances.

Figure 5: Appearance of infrared sensor

Figure 6: Internal structure and circuit diagram of infrared sensor

Ultrasonic sensors, which are similar to infrared sensors, have been used more and more in the automatic detection of moving objects in recent years. Ultrasonic sensors mainly use the Doppler principle to emit high-frequency ultrasonic waves that exceed the human body's perception through crystal oscillators. Generally, 25-40kHz waves are selected, and then the control module detects the frequency of the reflected wave. If there is an object moving in the area, the frequency of the reflected wave will fluctuate slightly, that is, the Doppler effect, which is used to determine the movement of objects in the lighting area, thereby achieving the purpose of controlling the switch. Figure 8 is an application solution for the combination of ultrasonic sensors and microprocessors.

Ultrasonic waves have longitudinal oscillation characteristics, and can propagate in gases, liquids, and solids at different speeds. They also have refraction and reflection phenomena. When propagated in the air, their frequency is low and they decay quickly, while in solids and liquids, they decay less and propagate farther. Ultrasonic sensors use these characteristics of ultrasonic waves. Ultrasonic sensors have the characteristics of a large sensitive range, no visual blind spots, and no interference from obstacles. This technology has been used in the commercial and security fields for more than 25 years and has been proven to be the most effective method for detecting the movement of small objects. Therefore, the system composed of LED lamps can sensitively control the switch.

Figure 8: Application of ultrasonic sensor and microprocessor

Due to the high sensitivity of ultrasonic sensors, air vibrations, ventilation, heating and cooling systems, and movement in the surrounding space can cause false triggering of ultrasonic sensors, so ultrasonic sensors need to be calibrated in a timely manner.

Temperature sensor NTC has been widely used for over-temperature protection of LED lamps at an early stage. If LED lamps use high-power LED light sources, they must use multi-wing aluminum heat sinks. Since the space of LED lamps for indoor lighting is very small, the heat dissipation problem is still one of the biggest technical bottlenecks. If the heat dissipation of LED lamps is not satisfactory, the LED light source will cause early light decay due to overheating. After the LED lamp is turned on, the heat will also accumulate to the lamp head due to the automatic rise of hot air, affecting the life of the power supply (Figure 9). Therefore, when designing LED lamps, an NTC can be placed close to the aluminum heat sink near the LED light source to collect the temperature of the lamp in real time. When the temperature of the lamp cup aluminum heat sink rises, this circuit can be used to automatically reduce the output current of the constant current source to cool the lamp; when the temperature of the lamp cup aluminum heat sink rises to the limit setting value, the LED power supply is automatically turned off to achieve over-temperature protection of the lamp. When the temperature drops, the lamp is automatically turned on again (Figure 10).

Figure 10: NTC overtemperature protection scheme

Conclusion

Because LED lamps are complete electronic products, with the diversification of LED lamp structures, the expansion of applications, and more creativity and innovation in the design of LED lighting fixtures, more sensors will be combined and applied in the systems of LED lighting and lighting projects. A new era of intelligent LED lighting is coming, and human lighting life will become brighter and more comfortable.