An app note (PDF) from KEMET on coupling two high lifetime devices: LEDs and Supercapacitors.
Light emitting diodes, or LEDs, have come to prominence in recent years in conventional lighting applications including flash lights, street lamps, traffic lights and emergency lighting. Their advantages over incandescent and compact fluorescent light sources include greater robustness, higher energy efficiency and a longer lifetime. Due to the constantly falling prices of LEDs, they are also now becoming more economical in the long term than traditional light sources.
Supercapacitors are high lifetime, high power devices that store relatively little energy compared to a battery. The low power requirements of LEDs means that a reasonably sized supercapacitor power source can still provide several hours of lighting on a single charge, while the high lifetime and low-temperature performance advantage over batteries is maintained. The emergence of 3.0 V supercapacitor cells as well as hybrids only strengthens the case for their use in LED applications due to the higher amount of energy stored in these new supercapacitor types. Supercapacitors are also free of lead, mercury, and cadmium, which eases any environmental concerns that may arise over the course of their long term use and eventual disposal/recycling.