A student laboratory experiment to investigate the intrinsic and extrinsic bandgaps, dopant materials, and diode design in light-emitting diodes (LEDs) is presented. The LED intrinsic bandgap is determined by passing a small constant current through the diode and recording the junction voltage variation with temperature. A second visible wavelength emission method is used to determine the active bandgap for comparative purposes. The active bandgap data is used along with literature values to interpolate the ratio of elemental dopant atoms in the LED semiconductor. This work also discusses the fundamentals of bandgap theory, LEDs, and diode design and how these experimental measurements correlate to the diode structure and dopant material used to manipulate the bandgap energy and observed emission profile. Suggested questions are provided in the supplemental materials to help students further explore and understand the topic. While this laboratory experiment was created for upper level undergraduates, it can be revised and simplified for use in high school and introductory level undergraduate courses.