Explain under what circumstances the LED "dome" is fragile?

[OneBigDay]

I have read a lot of posts in the past few months were people are complaining about the LED domes being knocked off. Usually this is not accompanied by a full explanation of how this happened. I am wondering if this is only something to be concerned about if you are doing mods and pulling the PIL apart, or if this is a more widespread problem. I am not talking about the case where people are removing the dome on purpose.

My observations so far seem to be this is more common with Luminous LEDs, and it also seems to be happening mostly when people are trying to focus drop-in reflectors or doing emitter swaps (mods). It seems that actually touching the dome is the shortest path to knocking it off. This is kind of the crux of my question - is the dome still somewhat fragile even if you do not touch it?

A lot of marketing hype has been put out there that LEDs are "virtually indestructable". If the optic/dome is an integral part of the LED package (which I believe it is), then how indestructible is the whole package in practical use?

I would like to hear the subject matter experts explain why is the dome fragile at all and how much does this vary between different emitters? I would also like to hear peoples comments or experiences with actual use cases in the following scenarios - which I would hope is normal use and would NOT result in a broken dome.

1) Weapons lights (can the impact from firing a weapon remove the dome?)
2) Bicycle use (say handlebar mounted on a hardtail bike on a rough trail, could this result in the dome coming loose?)
3) Accidental drop of a flashlight onto a hard surface where the host comes out reasonably ok.
4) Normal holster or bag use where the flashlight might take a few indirect hits but nothing purposeful or abusive.
5) Simple handling of drop-ins (moving between hosts, in/out of storage, etc)
6) Epoxy aging. Anybody familiar with CD rot? Your precious music/data is archived forever, unless of course the CD itself starts to break down over time. I know LEDs in flashlights are a relatively new technology, but I wonder how the dome bonding agents will hold up over time.

Any comments and/or experiences appreciated.

 

[carrot]

I have never managed to destroy a single LED, and I am very tough on my lights. I've been carrying the same Seoul P4-based light for the past 2 years and I've dropped it, thrown it, fell on it, you name it I've done it, and the LED is fine (so is the rest of it, thanks for asking). The Seoul P4 are also recognized as one of the more fragile power LEDs on the market, to boot. So I'd say, they're only fragile if they aren't encased in their usual glass-and-reflector habitat.

 

[Qoose]

Just for kicks, I have this bare rebel LED epoxied onto a piece of sheet metal. No optics, no flashlight body, no protection except for possibly a little drop of epoxy that might laced over the dome. Let's just say it's covered in dirt and grime, been cleaned a couple times by a clorox wipe, and does it's job sitting on the front fork of a bicycle. The dome is still there, and it still looks pretty darn bright.

 

[Robin24k]

Generally speaking, LED damage usually results from modifying the light. Certain LEDs are more fragile though. The Rebel is pretty good durability-wise.

 

[Locoboy5150]

I had that happen with my Terralux TLE-5EX, as described in this thread:

http://www.candlepowerforums.com/vb/showthread.php?t=251476

When I look back, about a week before the LED lens fell off I accidentally dropped my Mini-Maglite on a motel room's bathroom floor. It was a hard ceramic tile floor. I dropped my Mini-Maglite from a height of about three feet and it landed on the edge of the bezel. The bezel was not dented and the only visible damage at the time of the accident was a small scratch on the black anodizing.

I didn't think much about the fall because as you mentioned, LEDs are marketed as being much more durable than incandescent bulbs. The actual LED itself may indeed be durable, but the complete LED assembly, including the dome/lens isn't as durable as the marketing guys make them out to be based on my one experience.

If it matters, the TLE-5EX uses a Cree XRE LED. The Cree parts were what came apart, not the Terralux parts. Terralux replaced everything for me under warranty.

 

[Illum]

I have never managed to destroy a single LED, and I am very tough on my lights. I've been carrying the same Seoul P4-based light for the past 2 years and I've dropped it, thrown it, fell on it, you name it I've done it, and the LED is fine (so is the rest of it, thanks for asking). The Seoul P4 are also recognized as one of the more fragile power LEDs on the market, to boot. So I'd say, they're only fragile if they aren't encased in their usual glass-and-reflector habitat.

you never handled LEDs by hand have you =P
CREE Domes are hard, but vulnerable to lateral shearing...or excessive force applied from the side.
SSC Domes are like jelly, they will attract dust and will shatter or fracture easily under the slightest of pressure.

to an extent, LEDs are best handled by tweezers:thumbsup:

 

[OneBigDay]

Thanks for the comments all. I think I see the picture. Locoboy5150, sounds like you had a bad experience that turned out ok - Terralux backed up their drop-in.

Generally speaking this is the conclusion I was hoping for and it sounds about right

... they're only fragile if they aren't encased in their usual glass-and-reflector habitat.

Although probably impossible to comment on at this point, I am skeptical that these silicones and epoxy will hold up well over time. Not being a chemical engineer my skepticism rules over any empirical evidence or real knowledge on the topic. I also realize the flashlight (along with 1000 other electronic gadgets) is considered a commodity and disposable to some degree. It's hard to feel this way immediately after you've dropped 50-200 bones on a flashlight, but hey what can you do? :shrug: In the end, "the dome came off" may be just another reason in the long list of reasons to buy another light. I hope not though.

 

[carrot]

If it was actually a problem you'd see threads about it. I haven't. There are LED lights that have been in service for years without issue.