Why use "Gummy Bear" domes when Lumileds seems to have gotten it right?

Just wondering why a manufacturer would turn to "Gummy Bear" domes on an LED when other companies like Lumileds seem to have gotten it right with the much clearer acrylic domes?? Seems like a step back in opinion, especially when the Seoul P4 seems to be a superior part in terms of overall output. I just can't help but think how many more extra lumens could be squeezed out of this part by using a more efficient and clearer dome.

What are your thoughts on this, and what do you think the justification was for this move?

Re: Why use Gummy bears domes when Lumileds seems to have gotten it right?

I would guess there are clear design reasons for this that are not apparent to the individual user. For example most of the big users seem to use a lens rather than a reflector. It's cheaper for any number of reasons.
A gummy bear might allow lower tolarences on the lens and a better interface.

Find somebody who buys 100,000 of these a week and you might get an answer.

Re: Why use Gummy bears domes when Lumileds seems to have gotten it right?

The luxeon K2 is a gummy dome.
The luxeon acrylic dome will yellow with age/UV exposure. The SSC P4 says not to expose to UV, so I assume it has the same issue...

Re: Why use Gummy bears domes when Lumileds seems to have gotten it right?

Just grabbed a K2 led, and yes, it is a soft dome.
But not really gummy bear gummy.
Lumileds seems to have done good on that one.
Not sure why Seoul couldn't do as good as Lumileds did.
It's when the dome is gummy enough to attract a lot of dust is when there is a problem.

Re: Why use Gummy bears domes when Lumileds seems to have gotten it right?

Mike Painter said:

A gummy bear might allow lower tolarences on the lens and a better interface.

Find somebody who buys 100,000 of these a week and you might get an answer.

Click to expand...

Mike might be onto something here, maybe the soft lens moulds itself to the optic.
Norm

Show me a LED that is SMD compliant that has an acrylic dome or lens. As already stated, Lumiled's latest and greatest has gone to a soft silicone dome in the K2; well latest anyway.

It seems to me that the "good" LED's either have some type of glass or a gummy protection over the die. :shrug: I really like the XR-E package and the materials used with it. I feel the Seoul needs some special attention but it deserves such attention.

Nice thing is that the K2 doesn't act like a dust magnet.

The soft silicone domes are reflow compatible. Acrylic melts.

I finally realized the other item the Seoul P4 reminded me of, I have a lint roller that is sticky, much the same way, but it doesn't attract dust right out of the air like the Seoul P4 does.

Anyhow, all one has to do is to use them in a sealed light, and carefully wipe it a few times, right before installation into a sealed light. I've been wondering if the dust falls off if you dip it into a cup of Isopropyl Alcohol- something to try when I get a chance.

I think the gummy lens is the least of SSC's worries.

65535 said:

I think the gummy lens is the least of SSC's worries.

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Care to elaborate?

I think the gummy dome has something to do with the use of lens. When a lens joins with the dome it pretty much is able to mold with it and make the lens apart of the LED and thus helps with light extraction. That's my guess.

Just exactly what are the other "worries"?
You can't come out here and make a statement of this nature and expect to not be asked this question. Please be exact and detailed with your response or nobody will take you seriously. A pointer to another thread will not cut it BTW. First hand information is a plus here.

Call me crazy but I have a feeling that this choice has more to do with cost than almost anything else. Remember, they make these things by the 10's of thousands. When manufacturing electronics on this scale pennies can make a huge difference to the bottom line cost of manufacturing of a product. If a glass dome (and it's associated processes) costs 2.4 cents more than a gel dome and the real world performance is close to equal then a company is going to go with the less expensive process and or material. This can have a big impact on the bottom line of a growing company.
yaesumofo
Yaesumofo

65535 said:

I think the gummy lens is the least of SSC's worries.

Click to expand...

yaesumofo said:

A pointer to another thread will not cut it BTW.

Click to expand...

Why not? The information about SSC's poor design and assembly is available in other threads.

Why not? Because it is nothing new. and certainly does nothing to support his position.
I don't agree that SSC parts suffer from poor design or assembly. The sample size that the "other threads" are discussing, is way too small to base sweeping statements like yours ("poor design and assembly") upon to have them substantiated.
It is way too early to tell.

Yaesumofo
BTW I doubt that companies like SureFire would bet their success upon parts which are of "poor design and assembly"
I just don't see that happening.

chevrofreak said:

Why not? The information about SSC's poor design and assembly is available in other threads.

Click to expand...

silicon has much better thermal conductivity than epoxy resin.

I seriosuly doubt that there is any significant amount of heat dissipated through the dome. The primary thermal path is through the heat sink slug. Any additional heat dissiapted via the dome is purely coincedental and is hardly influential.

As Newbie said, a silicone dome will allow the devices to be reflow soldered.

tebore said:

Care to elaborate?

I think the gummy dome has something to do with the use of lens. When a lens joins with the dome it pretty much is able to mold with it and make the lens apart of the LED and thus helps with light extraction. That's my guess.

Click to expand...

That does sound plausible to me.. but i have to tell you that i would be pretty afraid to drop this into a flashlight that has an optic which screws down onto the LED. What happens when the LED dome and the Flashlight optic mate with each other? No real sign of contact since it's soft, and i would certainly be afraid of twisting the dome off. Anyone experience this before? I have just ordered 3 of these though so i should have a better understanding of the real world drawbacks or benefits to this type of dome. (for my needs anway..)

The theory of allowing for reflow soldering does also make allot of sense to me as well.

I think it is a refractive index matching thing. More light out the front of the assy.


Thurmond

you guys do realize that the Cree has a gummy too? It just has a hard outer shell. Under that shell is a gummy and the shell doesn't really stop the gummy from being damaged. I accidentally pressed down on the dome of a Cree emitter I was installing in a light, and some of the gummy material splooged out around the edges of the hard plastic shell The LED still lights up fine but I'm sure the beam is screwed up now by the mooshed up / no longer clear gummy material inside.

I was having bad luck that night though I guess because I also was soldering a Cree emitter onto something, and somehow the heat caused the metal ring to fall off... along with the whole lens. So I had a little ceramic emitter board with a naked LED die on it. It still lit up though, the light coming out of it seemed more yellow somehow.

Re: Why use Gummy bears domes when Lumileds seems to have gotten it right?

Mike Painter said:

I would guess there are clear design reasons for this that are not apparent to the individual user. For example most of the big users seem to use a lens rather than a reflector. It's cheaper for any number of reasons.
A gummy bear might allow lower tolarences on the lens and a better interface.

Find somebody who buys 100,000 of these a week and you might get an answer.

Click to expand...

The light extraction closes on perfection, if you use a silicone lens, and mold it around the LED in a similar silicone material.

Hellbore, are you talking about the XR-E? The XR-E uses a solid glass lens with a very soft gel inside. I seen from other posts and my own findings. I don't know about any of the other Cree parts, though.

I like the fact that was stated earlier. It is designed to be reflow soldered. It also gives you some added protection when you are soldering near the LED and you bump your soldering iron against the gummy dome of the K2 and SSC P4. It has saved the clarity on many of my LEDs so far. I have massed up the beams of some older Luxeons when I accidentally touched the iron against the dome. They also add some flexibility to the LED so some force on the dome does not totally mess up the LED bond wires and phosphor or cause the beam to be permanently distorted (like the Cree XR-E and some Luxeons, as we have found). I tried hammering a dud K2 with some pliers in an earlier experiment, and I didn't see any damage whatsoever. As you put some more force (and possibly frustration out) on the dome, it will mess it up though. Never tried it on a live one yet.

I have also heard that it helps dissipate heat a bit better than the acrylic domes. Just think, when you touch a K2 or P4 what is on at full power, you can feel the heat. That heat, although I agree isn't much, could be trapped in the LED dome like the older LEDs. I know the slug is designed to dissipate the heat, but the dome helps some. Any extra heat dissipation couldn't hurt, right?

I like it, but that is my opinion.


-Tony

Here's something to consider.

See the Cree XR-E star below. It had pressure on it during packaging and/or shipping, as you can see from the bag it was in.





Now if some pressure cycling can cause separation of layers, and subsequent loss of lumens, why wouldn't the cycling of heat potentially cause a similar delamination between materials?

P.S. The seller has taken responsibility and is sending a replacement