Light Intensity Sensor


A light sensor is a device for measuring the intensity or brightness of light. One of the most common and least expensive detectors that can be used when building a light sensor is a photoresistor. Photoresistors, also called light detecting resistors (LDR) are made from cadmium sulfide (CdS) cells that are sensitive to visible and near infrared light. The resistance of a CdS cell varies inversely with the amount of light incident upon it – bright light causes a low resistance between the two leads of the cell while low light results in a higher resistance. When a photoresistor is placed in a voltage-divider circuit, proportional changes in light intensity can be measured with the Vernier Analog Breadboard Cable.

Design Objectives

  • Build a sensor to measure changes in light intensity
  • Build a voltage-divider circuit with a photoresistor
  • Use a Vernier Analog Breadboard Cable to make the necessary connections between the light sensor circuit and the lab interface
  • Convert voltage values to a proportional measure of light


  • photoresistor
  • 5 kΩ resistor
  • breadboard
  • jumper wires

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Includes construction, software setup, calibration, and troubleshooting instructions.

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About STEM Sensor Projects

Buid your own sensors (BYOS) give students the opportunity to build their own detectors and measurement devices. Students will assemble an electronic circuit and then use Logger Pro software to convert an electrical signal to proper measurement units.

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