What are photoresistors?

What are photoresistors?


A Photo resistor, that is  also known as light dependent resistors (LDR), is a light sensitive device used to sense  the presence or absence of light and can also be used to measure light intensity  . When its  dark, their resistance is very high,  up to 1MΩ and in light their resistance drops dramatically to a few ohms, depending on the intensity of light. LDRs  sensitivity  varies with the wavelength of the light and known as non linear devices.

Analog Applications:

  • Camera Exposure control
  • Auto slide focus – dual cell
  • Photocopy machines – density of toner
  • Colorimetric Test Equipment
  • Densitometer
  • Electronics scales – dual cell
  • Automatic gain control – modulated light source
  • Automated Rear View Mirror

Digital Applications:

  • Automatic Headlight Dimmer
  • Nightlight control
  • Oil burner flame out
  • Streetlight control
  • Absence / Presence (Beam breaker)
  • Position sensor

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