Light Intensity Sensor

Introduction

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