STEM与日常科技·英语30篇（7）

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运动传感器如何在黄昏时自动点亮路灯

Streetlights now turn on automatically when motion sensors detect movement.
These sensors use infrared technology to sense heat changes from passing people or cars.
They also rely on ambient light levels to decide whether it is truly dusk.
A built-in photocell measures surrounding brightness and activates the system only in low light.
Once triggered, the sensor sends a signal to the lamp’s control circuit within milliseconds.
This avoids unnecessary energy use during daylight or when no one is nearby.
Modern versions combine motion detection with timers to extend lighting only for short durations.
Engineers design them to ignore small animals while responding reliably to humans.
The entire process requires less than five watts of standby power per unit.
This smart automation helps cities cut electricity use by up to thirty percent.