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Light Sensors

LDRs, photodiodes, phototransistors and digital lux sensors.

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  • LDR (photoresistor) — resistance falls from MΩ in the dark to ~1 kΩ in bright light; slow (tens of ms), non-linear; read with a voltage divider.
  • Photodiode — fast and linear current output.
  • Phototransistor — a photodiode with built-in gain; used in IR receivers and optocouplers.
  • Digital ambient light sensors (BH1750, TSL2591, VEML7700) — report lux over I2C, matched to human eye response.

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