Blackbody Radiation, Incandescent Bulbs and LED Detectors

The study of the quantum world often begins with blackbody radiation and Planck’s quantization hypothesis. While incandescent light bulbs have long provided light sources that closely approximate black bodies, the classroom investigation of this phenomenon can be limited by the need for spectrometers.¹ In this paper I examine the use of incandescent light bulbs to study blackbody radiation, and the use of LEDs as photodetectors to provide an accessible alternative to spectrometers. The dependence of the power radiated by a blackbody on the fourth power of the temperature is shown, as well as the dependence of the intensity of blackbody radiation as a function of temperature at discrete wavelengths in the visible and infrared portions of the spectrum.