To be fair, it is true that some LED Exit sign manufacturers do overdrive their LEDs which can lead to quick reduction in brightness and even catastrophic failure. And, a major exit manufacturer did recently discover their engineer(s) had selected the wrong LED. Those signs lost a great deal of their brightness in a very short period of time. We are all human. Though mistakes can be minimized, nobody's perfect. However, these are exceptions to the performance of well designed LED exits.

The use of LEDs in EXIT signs is not in question. It is the most reliable light source available to design engineers, today. However, there are calls from some quarters for new standards which require driving LEDs within their ratings. Good idea! (simple enough). LEDs do grow dim over time (20 years), but can also be over-driven into early old age, even to catastrophic failure, in almost no time at all. 

However, there is also a push for nationally recognized testing labs to test and list which LEDs are O.K. for use in EXIT signs. This effort to minimize mistakes seems laudable enough on the surface. And, "directly or indirectly, the existence or absence of formal standards becomes an issue in every product liability case involving alleged design defects"*. However, since improvements in LEDs continue at such an impressive pace, there is also a danger that unnecessary bureaucratic testing will hinder the cutting edge design process.