how do the streetlights turn on automatically at night? - solar street light with battery

On the fl Stone, a bird sits in the light and turns it on every night before going to bed.
In modern street lamps, when the amount of light falls below a certain threshold, a small circuit replaces the bird and turns on the light. A common light-
The sensing element is a photo of hydrogen sulfide-
Resistors, also known as CdS batteries. A photo-
The resistance changes its resistance according to the amount of light that hits it.
When a lot of light hits it, its resistance is almost zero. -
Its electrical conduction is very good.
It has a high resistance when no light shines on it-
It has a poor supply of electricity.
In a very simple circuit, you can connect the CdS unit directly to the relay (
Understand the working principle of the relay)
In this way, a large amount of light will power the magnet, and a small amount of light will not.
Normally, however, when the light hits the CdS battery, it cannot generate enough current to activate the relay.
Therefore, you need to add transistors to amplify the current flowing through the CdS unit.
A typical circuit may be like this: if a small amount of current flows from the emitter to the base, then a large amount of current flows from the emitter to the collector.
In other words, if the base is grounded, it turns the "switch "(
Path from transmitter to collector)
In this chart.
Therefore, when the light shines on the photoelectric tube, it turns on the transistor to power on the magnet of the relay, thus turning off the light.
The photoelectric tube has a high resistance when it is dark that day, so there will be no current flowing through the base and the relay will not be activated-
The light is on.
The circuit may be a bit more advanced under real street lights, but not a lot.
It has CdS units, transistors and relays, but it may require more than one transistor depending on the size of the relay.
It's really a very simple circuit!