Nitecore D11.2 suddenly changed to yellow tint

I have a ~2 week old D11.2 which suddenly developed an extremely yellow tint overnight. Previously, the beam was cool white, about the same as the IFE2. According to Nitecore's website, both lights have an R5 emitter, which makes sense as the output looked about the same (apart from brightness).

Here are the things I've tried so far:
- Changed the battery: The D11.2 has been using the same Eneloop AA since when I got it, so I thought the battery may be low. Fresh Eneloop has the same tint and brightness (hooray regulation!), and the battery runs another single AA R2 light identically to the fresh battery. This leads me to conclude that the battery is not at fault.

- Cleaned all of the threads and contacts: I cleaned all of the lube off the threads and piston and make sure the contacts were clean and shiny to see if there was anything affecting the circuit, but the results are the same. I don't have access to a multimeter at the moment to perform any measurements, but I presume they are functioning as they should.

Is there anything that would cause the tint of the LED to suddenly change? The light still ramps up/down as it should, so it doesn't seem like it is the driver. I'm at a loss as to why the light would become yellow overnight and any thoughts or explanations would be appreciated. I'll take some pictures to illustrate the change as soon as I can.

Thanks!

Does the LED itself look any different ie any discolorations? Usually LEDs shift blue if overdriven or overheat. So how yellow is it?

LED and beam comparison; D11.2 vs IFE2

The LED itself is only a touch less yellow compared to the one in the IFE2 (assuming that the R5 in both were initially identical): http://i.imgur.com/cj8P1.jpg
The D11.2 is on the left, IFE2 on the right.

The beam is much yellower (or is that a green tint?) than the IFE2. Originally they were the same tint. I had to take this picture at mid-brightness in order to not saturate the camera sensor, and I adjusted the contrast/saturation on-camera to visually match what I saw: http://i.imgur.com/T5dcx.jpg

I apologize for the picture quality- they were taken with my phone. I'll take better pictures later today when I have access to a better camera. Thanks for helping me out!

Re: LED and beam comparison; D11.2 vs IFE2

Sorry I can't offer any help with your problem. I will say my experience with Nitecore and Jetbeam products have been very poor with 4 out of 7 lights failing. Only one while still in warranty. Only two of the seven continue to work properly.

Guess I'm a little slow but Jetbeam/Nitecore no longer fall in my purchase window no matter how much I like the design.

Re: LED and beam comparison; D11.2 vs IFE2

I had a Fenix E11 which had a very green / yellow tint. When I took it apart I noticed that the dome over the LED was damaged. I wondered if the problem with the dome had anything to do with the colour of the beam?
This is the E11 compared to a 'normal' flashlight:




I also had a Nitecore EZAA which developed a fault with the LED over a period of about 4 weeks from new. When switched off it looked perfectly normal, but when switched on and the LED projected onto a wall through a lens, there was a black 'burnt?' area across the centre of the LED itself. This didn't affect the colour but did reduce the output and seemed to get worse over time.


So it may be that the LED has a fault, even if you can't see it.

I cleaned a light with contact cleaner and damaged the led. It ended up with a similar color tint so it may be the led phosphor breaking down

New photos, status update

As promised, some better photos.
http://imgur.com/5Dhyo - beam shots at full brightness
http://imgur.com/QQiR2 - beam shots at lowest brightness
http://imgur.com/IixM2 - emitter comparison; neither emitter is perfectly centered

I contacted customer service1​ and got a response with an RMA number within 15 minutes. I explored the idea of doing a neutral-white emitter swap, but a quick search didn't turn up enough resources to the point of confidence that it was feasible or I could find all the parts in a timely manner. I'll be sending it off tomorrow for an exchange.

Follow-ups to suggestions in the thread:
The best explanation for what happened was the LED was somehow damaged. I'm not sure how, though; during the day, it's either in my pocket or in use for a few minutes at a time. At night, it sits on a nightstand (standing up). The yellow issue exhibited itself before I cleaned off the contacts, and I used a paper towel and a cotton swab to wipe off the residue. Furthermore, the driver module is more or less sealed from the inside and I haven't tried to disassemble it (if it ain't broke2​). The LED to my knowledge has never been overdriven since the only power source was an Eneloop. In any case, the seller has already offered an exchange.

[1] I couldn't find a rule that clearly stated whether merchants could be named. If someone can confirm that I may, I will mention who has this great customer service.
[2] The engineer's corollary: If it ain't broke, it doesn't have enough features.

Update: Got the replacement in the mail today. It appears to be one of the older D11.2 variants with the 'V.2' stenciled on the side.

Some differences between my original one and the replacement:

• The tint is cooler/purplish more than the original one, even when compared against another R5. Variance is to be expected.
• The lens doesn't have the purplish coating on it.
• The button/piston sits further out to the point that the top of the o-ring gap is slightly visible outside of the housing. It is also easier to press1​.
• The head is ever-so-slightly thinner as a snug fitting bottle cap diffuser barely stays on.

Straight out of the box, it's clear that the replacement has previously been used. While HA was spotless, there were a couple of what appeared to be hot glue strands on the body2​. The piston end also had some scratches and a pinhole dent. Internally, the contact ring has a substantial amount of wear on it, to the point that the gold-colored plating has worn down to the silver base beneath and there are several dents exposing the aluminum on the inside of the head. The base of the piston button has a ring of vertical wear lines from button presses.

The wear on my original D11.2 was practically zero after two weeks of moderate use, so I can't even begin to estimate just how long the replacement was previously used. It remains to be seen whether the replacement is truly a revision 2 without the parasitic drain, but for all intents and purposes the replacement is a functional light. I am a bit displeased that a previously new, two-week old flashlight which developed a defect would be exchanged for one in a much older condition.

Edit: Adding additional information:
Photos for the interested: http://imgur.com/a/KnmY8#0

[1] This may be due to the spring and piston having previously been broken in
[2] The strands may in fact be from the foam insert. Similar threads were observed at the bottom of the cutout.

That's not good, I would definitely return it. You paid for a brand new light, you should receive a brand new light. Could you please let us know the vendor so I know not to purchase from them?

I will, in due time. I want to be as impartial as I can and give the vendor a chance to respond. I received the replacement on Saturday and sent them an email today (Sunday). I am not expecting a reply until 2 business days later, even though they responded within 15 minutes the first time.

I urge everyone following this thread to be patient and not make any rash judgements until we know the full story. I am giving them the benefit of the doubt, as the replacement light was in full retail packaging with the manual, warranty card, and even the desiccant pack in the light itself. Unfortunately, I didn't have the foresight to mark the one I returned to see if they just swapped it in. I do know that the packaging is not the same since a folded 'features' booklet wasn't attached to the replacement.

Be patient, and I will update with the vendor's response or in two days at the latest.

Received an email this morning with an RMA number to send the light back so they can look into it. The customer service representative who replied was confused as they do not ship used products.

Are you in UK by any chance? I had a similar problem with a light I returned. I worry that it is to easy with some packaging just to swap the lights over. The clamshell packaging is obviously more tamper proof and I admit I feel happier if a light is delivered in clamshell as I know it won't have been returned to vendor previously.

Also my Nitecore has no visible serial number so a 'swap' for a previously returned light would be easier for an unscrupulous dealer. Not sure why Nitecore don't number all their lights - even my relatively cheap Olight i2 and Fenix E01 have serial numbers on the heads.

I'm in the USA. It's also possible that it was a new to the vendor since it was a retrofit D11.2 (head shows D11, has V.2 stenciled on the body after the fact) and they received it that way from Nitecore.

Regardless, the box showed signs that it had been opened before. The box itself is a clear printed plastic and is quite brittle and easy to tear, and the corner of the box was already slightly torn.

We'll see how the second exchange goes and what they turn up when they look into the issue.