STEM与日常科技·英语30篇（7）
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How Motion Sensors Trigger Streetlights at Dusk
运动传感器如何在黄昏时自动点亮路灯
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Streetlights now turn on automatically when motion sensors detect movement.
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These sensors use infrared technology to sense heat changes from passing people or cars.
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They also rely on ambient light levels to decide whether it is truly dusk.
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A built-in photocell measures surrounding brightness and activates the system only in low light.
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Once triggered, the sensor sends a signal to the lamp’s control circuit within milliseconds.
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This avoids unnecessary energy use during daylight or when no one is nearby.
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Modern versions combine motion detection with timers to extend lighting only for short durations.
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Engineers design them to ignore small animals while responding reliably to humans.
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The entire process requires less than five watts of standby power per unit.
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This smart automation helps cities cut electricity use by up to thirty percent.