Nichia 219C, testing a 5000K 83CRI emitter, comparing with a XP-G2 S4 2B and other leds

^ Damn djozz. Beautiful craftsmanship there. Congrats and thank for all the tips you just gave. Looking forward to hearing more about how this dedomed emitter works for you.

Not only the skilled surgery, but check out the macro photography!

Anybody know if it will be offered in 4500 or 4000k? I suppose I could just shave the dome until I get the tint I want… Does shaving affect the CRI at all?

welight (=Cutter) said that they will have the 4000K 83CRI soon

in stock now

Are they on the website?

A bit disappointing result. I built the sliced Nichia 219C above into a UF-1504, with the prototype LD2 driver (that still acts funny when mode changing with the clicky, but high setting works). The current through the Nichia was 5.85A (long live the low Vf), about what the driver is supposed to deliver when in regulation, and close to the ideal current for the led for maximum output. According to the graph of the OP, the output of the Nichia 219C at 5.85A should be about the same as the output of the XP-G2 S4 2B at 4.4A. n10sivern measured this XP-G2 S4 2B led in a UF-1504 at 458kcd where the current was 3.8A. So if this Nichia would perform as well as a dedomed XP-G2, the throw should be above 458kcd, say 480. But what I just measured was just 296kcd, that is 40% less, way less than what any of the normal variations, like lens quality, bin, focus can explain . So this sliced led does not behave like a dedomed Cree led for whatever reason. (or something else is wrong, I ruined the led somehow, I don't know).

The beam is nice enough, a perfect evenly illuminated square (with some 'corona' around it caused by diffused light through the leftover silicone at the side of the die) of very nice tint, but what counts in the end is sheer throw of course. A quick beamshot (not completely sharp focussed):

Has anybody tested or have theories on the affect of shaving or dedoming on CRI?

I still have a couple 5000k sitting on my desk, but I prefer 4500k. I’d be awesome if shaving can get the tint there, but pointless if I lose the High CRI in the process.

I’m guessing it has to do with the surface quality of the sliced face scattering the light coming from the LED. Thoughts?

Essentially like a dirty dome? I know I have seen threads of people polishing sliced domes.

Of the (many, various) 80+ CRI leds that I dedomed thusfar, dedoming makes the tint warmer but the tint always stayed nice, and colour reproduction stayed good. I can not measure CRI, so it is a guess, but I think CRI is not much ruined by dedoming.

This shaved Nichia 219C led I guess at 4500K, so it had a limited tint shift (may or may not have something to do with the quality of the dedoming effect)

My gut tells me that CRI is the product of the phosphors used, therefore unaffected by dome slicing. But obviously the dome has an affect on tint, so…… I wonder if MEM has tools for measuring CRI….

A lot of high-CRI led have the magic high-CRI producing fairy dust mixed into the dome material. I saw some microscope shots of some Nichia LEDs where red granules were embedded in the dome.

Yes they are

We do a lot of spectral testing here for customers, as a comparative point. When you test with and without a secondary optic you can get up to 300Kelvin shift, the logic would say a dome on a led is a primary optic so the same shifts should be expected

Djozz, they are the same dome style as a 219B, correct? Very similar? I have dedomed a few 219Bs, they can fool you. Nichia has a clear-coat layer ON the phosphor. It’s perfect after the de-dome, to explain what I mean, the die looks like one of these CREEs after a de-dome (picture below), making you believe there’s extra material stuck on because it’s glossy—I found it to be filled with phosphor. You do not want to remove the glossy layer after the dome, then.

I use a 2-step de-dome procedure now that is a chemical de-dome in about 4 hours, I did a time-lapse video showing the dome detach right around 4-5 hours if done with a fast solvent followed by a slow solvent because of varying plastic types in the dome. I first attack the base glue, then swell the dome until it pops by itself. No slitting, I do not touch the dome.

MEM, in your opinion should the CRI be unaffected by dedoming or slicing as long as we don’t remove that layer you described?

Sorry, I had completely missed where you had asked about CRI measurement before I last posted. I have a tendency to catch the start/end of threads when I’m in a hurry to read. I need BLF-subscribed posts on a 24/7 audio translated PA stream that I can listen to as they come in over horn speakers throughout my home and shop. :bigsmile:

OK, to explain this, you must first understand how difficult it can be for one to fully explain. Even the simple answer of a yes or no, it’s always dependent on a few different refractive properties, phosphor thickness, bonding, sealing layer contour, etc etc. IMO, I think a good de-dome is still going to change CCT noticeably enough. However if you read on…

We deal with two primary rating systems: CCT & CRI. We expect CCT to directly impact CRI-rating, in some reasonably predictable fashion. People go as far to assume this is an automatic change and the two are linked. We know CCT will change with a de-dome, and that means a CRI change. Well, technically that is not true. CRI is independent.

About the CRI, first of all. The latest “news flash” of high-lux LEDs that also have a “high CRI” rating is something we mostly have not been used to seeing or hearing about—especially when our focus gets affixed on CREE LEDs and their numbers. These trends tend to form opinions about CRI with some mistruths involved about de-doming. I would highly recommend that you read this webinar from OSRAM Opto, about the entire nature of CRI, and newer CRI rating types which exist (Ra, R9), that take things like color saturation into consideration, as well. This PDF will help many better understand how “CRI” is developed, what “CRI” actually is telling us, and also how effective the CRI rating system can and cannot be across the large scope of all available LED choices out there.

The PDF webinar is for download here: CRI Sources Explained

So even though intensity increases, and CCT will change, the same colors are technically still there in the LED. Those individual wavelength regions are further influenced by lens design, such as if the lens collimates all available colors at the same image projection without throwing some color away, due to aberration, for example.

I have a method I feel might possibly work. I have a 50”x50” fresnel lens in a frame, with a white wall near the back. The effect is interesting, because the fresnel seems to take on the full tint of the projection, and it is this displayed, like a TV channel. So I’ve wondered about the Adobe CIE color system combined with “RAW” photos. Let’s say I aim the camera so that the entire image is the fresnel lens lit by an LED projection, the photo should measure the tint, to some degree better than a human eye I would expect. This data can then be seen in Adobe. So I would setup, take a few baseline images, then de-dome, redo the test, and see what Adobe says the new CIE data is composed of. Seem or sound logical? I haven’t tried this yet, until I realized how well the entire surface took on the tint, even if hit by a 3x3” square of light, the entire lens still glows evenly. I could do some tests, but I haven’t thought this all the way through, so I don’t know if it truly is a good idea to start doing. I suppose it’s better than catching the pure hotspot alone in a photo and trying to analyze that—then other tints are involved (from small objects, wall reflections, etc) and would create erroneous (though possibly minute) extra color data.

I will try it, but must get some bezels turned out right now. Cerakote runs in the morning. Won’t be tonight.


I think I understood most of that. I’ll be interested in the results if you do decide to do some kind of test.

However, maybe I should just convince myself that slicing the 219c’s dome will actually improve the CRI, then live in blissful ignorance of the fact that I am probably wrong. It’s all in the head.

I can say this much. A solvent de-dome provides much cleaner and more repeatable de-domes (especially on hard to do emitters, apparently Nichia for those doing “hot” de-domes). CRI should not grow higher necessarily. CCT just drops in kelvin. This doesn’t expand the color range to include any more red, for example, or any more colors, just slightly changes their ratio. This is why I posted the PDF.

A LED dome is made to take on heat and stay bonded to the phosphor (to extent). It’s not made to resist solvent. Attack it at the weakest link in the chain. Only makes sense. A dome has enough buoyancy to “pop” after a swell, and lift itself right off with a very small swirl of the fluid if still attached anywhere. If you’re not having this happen, something isn’t right. Like I said, I never slit domes, that is to finish, or to provide a de-dome aid. The plastic is highly porous when in solvent, slits aren’t needed and will possibly negate from the desired “full dome” lift.

After a de-dome, untouched by tools/razer, a full dome lies at the glass bottom: