light dependent resistors

• Light dependent resistor (LDR)


  Also called a light dependent resistor
• LDR


  • Has high resistance in dark conditions
  • Has low resistance in light conditions
• How LDRs can be used in circuits

  1. LDR in series with lamp

  2. Cell provides 10V potential difference

  3. In light, LDR resistance is low so potential difference across lamp is high, lamp lights up

  4. In dark, LDR resistance is high so potential difference across lamp is low, lamp dims
• Devices using LDRs


  • Mobile phone screen backlight
  • Garden lamps
• LDRs can be used to detect light and turn devices on/off accordingly