An inexpensive LED light sensor

Light irradiance measurements are important for students grappling with abstract optical phenomena such as the inverse square law,¹ polarization, diffraction, interference, and spectroscopy. A variety of commercial light sensors are available from scientific vendors such as the CI‐6504A from PASCO scientific² and the LS‐BTA from Vernier Software and Technology.³ These sensors, in combination with data acquisition interfaces, allow students to digitally record relative irradiances. Many experiments in elementary lab situations, however, do not require this level of sophistication, and a simple LED connected to a voltmeter performs admirably as a readily available and inexpensive photosensor. LEDs are frequently used in the laboratory as light sources,^4,5 but their use as photodetectors^6,7 is relatively unknown in the physics teaching community. Here we introduce a few of the basic laboratory applications of common LEDs as photosensors.