LED stands for Light Emitting Diodes. This electrical components are basically nothing but a P-N junction semiconductor device. The only difference is that when current flows through the P-N junction, it induces photon emission. This emission of photons is directly proportional to the current flow through the P-N junction. In another word, when junction current increases, the amount of light induced by emitted photons increases.
It is important to understand the limitations of driving and LED. As a P-N junction device, current flow beyond the junction breakdown will cause the junction to heat up and melts. In another hand biasing the LED with a reverse bias voltage prevents the current flow (no photon emission) unless the voltage exceeds the break down reverse voltage. In this case, LED will be permanently damaged.