Lumileds Luxeon V, test of a 4000K 70CRI emitter

Dang, dang, dang…
The other one went bad too…

Both never saw more than 3 Amperes and never ran hot, but both are bad now, same problem… (see picture in my previous post)
I was about to order a couple more, but i’m not going to now.

So i want to ask you who have a Luxeon V in use to check out how it looks on a white wall focussed with a lens.

I guess that I am lucky thusfar, I have used the Luxeon V in 4 builds sofar and they all do not show this. All on moonlight, left to right: E2L, D4, VG10, S8-clone. Btw, you can see PWM in three, they have a BLF-A6 driver, the D4 uses higher frequency PWM probably.

I bought some Luxeon V’s , I don’t have a lens to try with but here is a couple of photos through a welding glass :
X6 (left) D4 (center) Sofirn C8 (right)

It’s the best picture I could take by they seem uniformly lit when I check under the magnifying glass, they have not been spared in any way they are both used with a FET driver and a Sony VTC6’s.

It looks like some blue light seeps through at the underside of your faulty led and that gets me to the following hypothesis: can it be that the dome had some sideways force and has party detached from the die? With the phosfor coming off with the dome (like with all new leds except the SST-40), the air in between die and phosfor prevents part of the light to enter the phosfor (various surface reflections) and escape back into the die or sideways. The phosfor above the detached part would appear darker then.

Looks like the defect has not manifested in the 4 in my Q8 yet. These poor guys got reflowed no less than 8 times. I have 6 more that I'm trying to figure out what to use them for. I'll report if any of them have the half dying issue. I have to say it again. I just love the tint and beam pattern with this emitter. The below pic is bottom of Ramp Mode.

Same here: several Luxeon V damaged the same way, but they got higher currents. The typical appearance as can be seen in Jerommels photos: about the third part (rectangle shaped) at one side of the die is darker.
Note: this is not always visible in low moonlight level! It can better be seen at higher currents through some filter (I use a writable DVD for this purpose).

Edit:
My LEDs were only mounted in reflector lights, so a force to the side of the LED is unlikely.

I will try the same picture tonight with the 4 lights on max. With some 10.500 lumen pointing at the ceiling I hope that no one will be disturbed :open_mouth:

The pictures I posted is taken on max output, I have build two quads and two reflector lights, I can’t see any irregularity’s in the die output in any of them.

I have been running them all hard and hot with FET drivers and VTC6’s and VTC5A’s.

Still trying to figure out if this is a random thing going on:
At what temperature do you reflow, Jerommel/Flashy Mike?

I haven’t reflowed them by myself, got them mounted on MCPCB, just like Jerommel (I guess).

That should be very ok, I trust led4powers reflows way better than my own.

I got them reflowed on 4040 boards too.
Very well done reflow indeed.

That’s the weird thing.
When you test them with very low current, it looks fine.

No mechanical damage on mine either.
The picture does show a small slightly blueish area, but that’s because of a sloppy, hastily put together aspheric test set up.

No, it’s just a sloppy set up, the lens was at a slight angle. Prism like tint shift effect.

Seem like the failures are most likely a manufacturing defect (as opposed to a design defect) as mine have been tortured with excessive handling and heat from reflows and high current. Took a pic in Turbo mode under welding googles:

EDIT: I just reread the above posts at the problematic emitters. I missed that one was working fine and then went bad. Seems unlikely to be a manufacturing defect when that is considered. Djozz's hypothesis makes a lot of sense. Would be informative to see how evenly the failed emitters lighted up with the domes completely removed.

If I remember right maximum current decreased also when the LED got damaged. Don’t have a flawless LED currently for comparison.

^

When you look at that emitter from the sides that the thermal pads extend out to, do you see indication that there is adequate solder between the emitter's thermal pad and the base?

EDIT: That may not work. The thermal pads don't extend all the way to the edge. Probably the best that could be done is to unreflow the emitter and see if it appears there is an adequate amount of solder on the thermal pad.

Checked 2 boards, there was no excessive solder on the visible ends of the center pad. So I unsoldered the LEDs and there is solder on the center pads of LED and board.

^

Thanks for checking. We expected that based on who reflowed the emitter, but it would have explained the drop in current and damage to your emitter if you had found otherwise.

If you don't think you will ever use that emitter in its current state, you could try a hot dedome. I would do it by reflowing it back onto a base. Before it cools (but after solder locks up), lift off the dome with a pick. The dome might break up. If it does, just try to lift of as many pieces as you can while trying to not remove phosphor. If you do remove phosphor, that is ok, but you will be left with a UV or Royal Blue emitter. After the emitter cools and you hook it up, put on some UV/Blue eye protection (if you lost phosphor) and power the emitter up. If the light is now evenly spread across the die, djozz's theory is correct (i.e. There was some separation of the dome from the phosphor) and you now have a dedomed Luxeon V.

Because?
What if the chip wasn’t properly soldered to its 4040 base?

You can hypothesise all you wish, but the LEDs were not mechanically abused, only saw 3 Amperes max.
The blueishness is only there in the picture because i had the little aspheric a bit askew.
You can see on the opposite side the yellow sticks out.
(I thought i explained that already…)

@ImA4Wheelr:
I might try that when I find the time but that wouldn’t explain the lower maximum current after the damage, I guess. I don’t know how this LED is build but I rather suspect some broken electrical connection in the LED. My damaged LEDs look exactly like the one shown by Jerommel, and with a separated dome I would expect some variation.