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VEX Light Sensor

Light Sensor

P/N: 276-2158

The Light Sensor uses a photocell that allows your robot to detect and react to light. With the light sensor, you can program a whole new range of capabilities to your robot. A Programming Kit is needed to change the program in the VEX Controller.

  • Analog input of light levels
  • Usable range of 0 to 6 feet
  • Find dark or bright areas
  • Create more autonomous function

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Function: The Light Sensor enables a robot to detect light. Robots can be programmed to have a specific reaction if a certain amount of light is detected. The Light Sensor uses a cadmium sulfosolenide (CdS) photoconductive photocell. The CdS photocell is a photo resistor, meaning that its resistance value changes based on the amount of incident light.

Uses: Design a simple tracker that follows the beam of a flashlight, or use a light sensor to help your robot to avoid getting stuck under furniture by making it steer away from shadows. You can even give your robot color vision by putting colored filters on different light sensors!

Benefits: The light sensor can give the robot vision and make it easier for it to operate autonomously.

The Light Sensor allows the robot to follow a light source, such as a beam of light from a flash light or similar. The Light Sensor is placed on the top section of the robot or on a lower section that is not covered. Figure 2 shows the sensor placement. This sensor can be used to help the robot avoid getting stuck under furniture. The Light Sensor can enable your robot to detect and follow a beam of light, or avoid getting stuck underneath furniture by avoiding shadows.

Figure 2. (a) Bumper Switch Placement; (b) Placement Close-Up

Figure 3 shows Squarebot following a light source placed above it. In conjunction with clever programming, it can be used to conserve battery power by shutting down the robot in the absence of light. In conjunction with filters, the robot can be given color vision to detect various colors.

Figure 3. Squarebot following a light source

The Light Sensor can detect distance accurately from 0-6ft away, depending on the intensity of the light source and the intensity of the ambient light. Consider the following example. It is easier to see a flashlight in the dark than it is outside on a sunny day. This applies to light sensors just like it does to humans. Light Sensors can only detect visible lights, just like humans. It can see everything we can see, and cannot see things we cannot see as well, such as infrared and ultraviolet light.

Technical Specifications

  • (1) Light Sensor
    • All VEX microcontrollers
    • 3-Wire Extension Cables


    • Type: Light

    3-Wire Cable
    Connect to an analog input

    • Black: Ground
    • Red: +5V
    • White: Control Signal
  • Sensor: cadmium sulfosolenide (CdS) photoconductive photocell
  • Sensor Type: photo-resistor
  • Actual Weight (one item, no packaging): 0.026 lbs (11.8 grams)