Diodes, specifically light-emitting diodes (LEDs), emit light when current flows through them, but not all diodes have this capability. In devices that convert AC to DC, standard diodes do not shine brightly; they function primarily as rectifiers. The discussion clarifies that only LEDs are designed to emit light, while other diode types serve different purposes. The mention of various diode types highlights the diversity in diode functionality beyond light emission. Understanding these distinctions is crucial for applications involving diodes in electronic circuits.