As seen from the data presented above we can conclude that
the LED life time depends very strongly on the temperature and
driving current conditions under which the LED is operated. If
we take into account that a higher current leads to a higher
junction temperature, we can speak from the effect of intrinsic
heat. This is generated from two sources – the LED die and the
phosphor layer. It is important to examine which parts of the
LED package cause luminous flux degradation. An interesting
study is to measure the thermal resistance of the LED during the
test and try to find out if there is some correlation between
luminous flux decay and increase of the thermal resistance R .
th.