I wanted to add that NEW green LEDs use InGaN but older ones did not (they were GaP or GaInP or AlGaP). See http://en.wikipedia.org/wiki/LED#Colors_and_materials On Fri, Jul 4, 2014 at 7:19 PM, Sean Breheny wrote: > > 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, the= re > were really only IR, Red, Orange, Yellow, and Green LEDs. There were a fe= w > 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 pe= r > 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 le= d > 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 solarizatio= n >> of the plastic or whatever else is used to cover the LED chip itself. T= his >> 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 .