I think that there were rapid developments in LEDs in the mid 1990s which changed the technology used for several types of LEDs. Prior to then, there were really only IR, Red, Orange, Yellow, and Green LEDs. There were a few Blue ones but they were very dim and expensive. There were no "super-bright" LEDs in the modern sense. I believe that some of the new materials (InGaN being one) which were developed then allowed not only cheap, high-brightness blue LEDs but also allowed the light output of the other colors to be drastically increased. I think there was a trade-off made, however, in terms of life. It seems to me that 1980s LEDs last practically forever but are very dim, whereas newer ones which are MUCH higher light output (both in terms of light output per mA of current AND in maximum achievable light output) have a service life measured in the 10s of thousands of hours at typical operating currents. I don't have an overall explanation but it really does seem to me that something changed in the way LEDs were made in the mid 1990s which has led to much faster darkening/ageing effects in LEDs. On Fri, Jul 4, 2014 at 5:48 PM, Robert Dvoracek wrote: > Green LEDs would be expected to age in the same way if it is the wafer > itself that is aging since they are essentially made from the same thing > (InGaN). It could be that the shorter wavelength is causing solarization > of the plastic or whatever else is used to cover the LED chip itself. Th= is > is especially seen in UV emitters that have plastic encapsulation. > > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .