Street lamp is a tool to provide road or traffic lighting. In order to save energy, a kind of street lamp with "energy-saving" function came into being. This kind of street lamp doesn't shine during the day. At night, when someone or car passes by, it will automatically light up and go out after a period of time. What's the reason?
There is a kind of resistance that is very sensitive to light. People call it "photosensitive resistance". When the brightness of the environment changes, the resistance of the photoresist will become smaller. Later, in order to be convenient, people made use of this characteristic of the photoresist to make an electronic device called "brightness (illumination) sensor", which will detect the brightness of the environment. Through this sensor, the brightness of the external environment is known, so that the street lamp can be lit at night.
However, even at night, it is not necessary to keep the street lights on all the time, as long as the lights are on when someone or a car passes by. When people pass by, there will be footsteps, and when the car passes by, there will be the "buzzing" sound of the engine. Similarly, there is a sensor that is sensitive to sound. This sensor can make street lights light up only when people pass by.
Frequently switching on and off the lamp will greatly shorten the service life of the bulb. For this kind of inductive street lamp, if it is installed on the roadside, it will not take long for the bulb to break because it is frequently switched on and off. The service life of the lamp can be maintained only by reducing the number of times of switching the lamp. What's the solution? The electronic engineer can set the timing function for the street lamp, so that after the street lamp is turned on, keep the street lamp on for a long enough time, and then turn off the street lamp after confirming that no one or car has passed.
For many mobile phones, if you look carefully, you will find that the brightness of the mobile phone screen changes indoors and outdoors. In the dark, the screen is slightly darker; In the bright place, the screen will be slightly brighter. In fact, this is the same truth.