We propose some experiences, using spectrometric measurements, to show students how different media and different light sources have different behavior. We start by measuring several light sources with the help of a fiber optic spectrometer. This device allows us to demonstrate how different white-light sources can be distinguish by the wavelengths that compounds the source. In other words, the visible spectrum. Even monochromatic light sources, which have the same color when observed by the naked eye, can be characterized. With this experience, we want to study several materials by means of the measurements of the reflectance and transmittance. To do that, we propose the characterization of some light sources and the observation of how their spectra change when the light is transmitted or reflected by the material. It is important to remark how the fiber or propagation media can affect the source spectra. We show the method to characterize the light source in conjunction with the optical fiber. This experience is performed with students inside the unit entitled “Radiometry and Photometry” of the subject of “Fundamentals of Engineering Optics”, basic subject included in the second course for obtaining a Degree in Telecommunication Engineering and “Optical Image Acquisition and Processing”, from the Master in Robotics-Automatics, both taught at the University of Alicante.