LEDs do not like high temperatures.
One of the few ways you can damage an LED is by applying too much heat.
LEDs do not like to be at temperatures above 250 degrees for more than a few seconds. If you overheat an LED when soldering you will reduce its life-span, or may even cause it to fail immediately.
Solder melts at a little over 200 degrees, but your soldering iron will heat your LED up much higher if you don't take it off the soldered joint as soon as possible.