MIT physicists developed an LED that emits more light energy than the electrical energy consumed. These LEDs supplement electrical energy with heat from the surrounding environment. Unfortunately this has only been observed at very low power levels.
The researchers chose a light-emitting diode with a small band gap, and applied such small voltages that it acted like a normal resistor. With each halving of the voltage, they reduced the electrical power by a factor of 4, even though the number of electrons, and thus the light power emitted, dropped by only a factor of 2. Decreasing the input power to 30 pW, the team detected nearly 70 pW of emitted light. The extra energy comes from lattice vibrations, so the device should be cooled slightly, as occurs in thermoelectric coolers.