Most common Luxeon failures??

I have been searching old posts and notice that Luxeons are very sturdy however they do sometimes fail.
Can someone give me a little information on the most common types of failures?...I am mainly referring to the 1 and 3 watt Luxeons.
I have often read where luxeons fail after being dropped with one of the leads being broken off or actually shifting on the board. Is this the most common failure and if so what lights are mostly immune to this?
I remember my friend Owen receiving his older model LongBow and he removed the head where we were looking at the circuit board. The entire board appeared to be sealed in a thick,hard epoxy with nothing at all exposed. The epoxy was filled all the way to the very base of the emitter thus covering up the leads with epoxy also.
Is this type of potting done in an effort to prevent this type of failure..(dropping)
I thought it was a pretty neat set up and was curious why it was built this way.
So if you have had any Luxeons fail what were the causes and what could be done better to prevent the failures?

The most common failure is probabbly due to the owner trying to fix what ain't broke! /ubbthreads/images/graemlins/grinser2.gif

i find they fail right after the smoke leaves them
do something to keep the smoke in, and they should last forever

reversed polarity with enough voltage... poof! /ubbthreads/images/graemlins/crazy.gif

I'm glad to say that I and others have dropped my luxeon lights while they were on and they kept going strong. (Hey, that rhymes. /ubbthreads/images/graemlins/grinser2.gif)

Those lights were my XM-3, it took a hard fool onto the conrete and my Lux III mag also took a hard hit. I've yet to have a luxeon fail.

I'd say the most common cause is probably overcurrent causing a failure of the bond wires. At about 3A of current, the bond wires burn open like a fuse. I have repaired several Luxeons with this failure (it was a big pain). The Luxeon III and one Luxeon I continued to work normally. However, the remaining Luxeon I would not emit any light with less than 200mA of current. So there is also some damage to the die that goes with the bond wire fusing.

My Costo 1w 2AA dropped about 2ft onto it's bezel on a concrete sidewalk and died. It appears that something came loose inside the "pill". The LED istelf works fine with battery voltage applied directly to it and another "pill" works fine in this light body.

I realize many people experiment with different combinations and have sometimes smoked a Luxeon. I was reading old posts and noticed many stated that their Luxeons quit working after some form of drop or impact.
I was mainly concerned with failures resulting from a weakness with the Luxeon when used normally or within specs.
With all things considered within specs are the actual thin leads the most weak part of the Luxeon?
I see many claims from makers who say the Luxeon never blows and will last a lifetime if ran within specs. This is good however if some fail when dropped is it usually the lead wires being sheared away.
I have been bitten by the Luxeon bug long ago and am simply wondering what the main weakness is of the Luxeon. Basically if the user runs the light within specs would impact be the biggest concern?...And if a drop or impact was the biggest concern is this why LongBow decided to surround their Luxeon and board completly with epoxy?

Hello Robocop,

I have a BB400 that was installed in an AA Mini Mag that was dropped onto concrete. The lens on the LED came loose. It still lights up, but it is very blue and is no longer focused.

I was surprised that it still works.

Tom

I have had 1 dead Luxeon so far. It was a Luxeon 1 star in a Chinese made flashlight (yes, it was a real Luxeon, not a copy /ubbthreads/images/graemlins/wink.gif ) and when I disassembled the flashlight, the lens got off the LED. It didn't work anymore...

Never had a failure because of overvoltage or too many ampère. I've tested Luxeon 1's at 5 V and Luxeon 3's at 1.5 A, but they still work. Of course I did those test for only a few seconds, because the LED became very very hot /ubbthreads/images/graemlins/tongue.gif

I have seen the LongBow pot the entire assembly and now noticed mt Pelican M6 is a very sturdy design. The board is sealed and the Luxeon is recessed inside the heatsink. The only thing visible is the top of the Luxeon dome.
It seems to me that some designs would be more resistant to failure from a drop than others. The LongBow and pelican have the design I like and just look very solid.
The way the Pelican M6 is made it seems like the dome could not really move if it were dropped. Is the pelican design made to transfer heat better or is this design for protection from a drop or impact?