The TI Light Probe is a budget light probe for measuring relative brightness. It senses both IR and visible light. The reading reported is a relative number between 0 and 1. Its low cost and ease of use make it an excellent choice for elementary and middle school.
The Vernier Light Sensor is also available, offers greater accuracy and measures three different illumination ranges.
Experiments and Lab Ideas
Elementary Science with Vernier (6)
Includes student instructions, teacher tips, safety information, and sample data.