The video discusses how streetlights know when to turn on and off. The host dissects a photocell light control, which contains a light sensor (photoresistor) and a thyristor that acts as a power switch. The photoresistor's resistance changes with light, and when it's dark, the resistance is high, allowing the thyristor to activate and turn on the light. When light hits the photoresistor, its resistance falls, and the thyristor doesn't activate, keeping the light off.
The host also examines a more robust version of the photocell light control, commonly used for streetlights. This version uses a thermostatic switch, a heater circuit, and a photoresistor. When it's dark, the heater is off, and the switch is closed, allowing the light to turn on. When light hits the photoresistor, the heater turns on, warming up the thermostatic switch, which opens and turns off the light.
The host notes that this design is different from older versions, which used a bimetallic bar and a spring-loaded switch contact. The new design is simpler and more cost-effective. The host also discusses the possibility of using microcontrollers and software to control the light, but notes that this approach has its own trade-offs, such as the need for a power supply and the potential for software issues.
Overall, the video showcases the creative and sometimes unconventional ways that electronic components can be used to solve real-world problems.
Here are the key facts extracted from the text:
1. A photocell light control is a device that uses a light sensor to turn lights on and off.
2. The light sensor is usually a photoresistor, also known as a light-dependent resistor (LDR).
3. The photoresistor changes its electrical resistance based on the amount of light that hits it.
4. When the photoresistor is exposed to light, its resistance decreases, allowing more electric current to flow through it.
5. The photoresistor is often used in a circuit with a thyristor, a semiconductor that acts as a power switch.
6. The thyristor is normally closed, but when it receives a control input, it opens and interrupts the circuit.
7. The circuit also includes a resistor that provides a path for current to flow to the thyristor's gate.
8. When the photoresistor is in high resistance (i.e., it's dark), the resistor provides enough current to activate the thyristor, allowing the light to turn on.
9. When the photoresistor's resistance falls (i.e., it's light), the resistor's current is bypassed, and the thyristor doesn't receive enough current to activate, so the light stays off.
10. Some photocontrols use a thermostatic switch, which opens when it gets too hot.
11. The thermostatic switch is often used in conjunction with a heater circuit that gets hotter when more light hits the photoresistor.
12. The heater circuit is usually powered by a small amount of current that flows through the photoresistor when it's exposed to light.
13. When the heater circuit gets hot enough, the thermostatic switch opens, interrupting the circuit and turning off the light.
14. Some photocontrols use a bimetallic strip that bends when it heats up, actuating a switch.
15. Photocontrols can be used to control streetlights, which often have a high power consumption.
16. Older photocontrols may use a different mechanism, such as a bimetallic bar, to actuate a switch.
17. Modern photocontrols often use a simpler design with fewer components.
18. Photocontrols can be designed to control multiple lights at once.
19. Some photocontrols use a microcontroller to introduce hysteresis and improve performance.
20. However, microcontroller-based solutions may have higher costs and be more prone to failure due to environmental factors.
21. Photocontrols can be designed to consume minimal power while still providing reliable performance.
22. The power consumption of photocontrols can be minimized by using a single control unit to control multiple lights.
23. Photocontrols can be designed to provide a delay between the time the light is turned on and the time it is turned off.
24. The delay can be useful in preventing the light from turning on and off rapidly due to changes in lighting conditions.
25. Photocontrols can be designed to provide hysteresis, which prevents the light from turning on and off rapidly due to small changes in lighting conditions.