Semiconductor materials are at the core of electronics. Most electronic devices are made of semiconductors. The operation of these components is well described by quantum physics which is often a difficult concept for students to understand. One of the intrinsic parameters of semiconductors is their bandgap energy E[subscript g]. In the case of light-emitting diodes (LEDs) E[subscript g] fixes the colour of the light emitted by the diodes. In this article we propose an experiment to compare E[subscript g] of a green LED obtained by both electrical and optical measurements. The two slightly different results can be explained by the theoretical knowledge of students on solid physics and the internal structure of electronic devices.