A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it. A semiconductor is made of a positively charged and a negatively charged component. The positive layer has openings or holes for electrons while the negative layer has free electrons floating around in it. The flow of electrons from the negative to the positive layer is activated when an electric charge strikes the semiconductor. As the electrons flow into the positively charged openings or holes, they emit light. What this all means is that a diode produces light when a charge, or power, is applied to it. As a result of the charge, the electrons want to move and this movement creates light.
An incandescent bulb works when electricity flows through a filament or small wire. The filament or small wire gets so hot that it glows and emits light.