Yeah, my D25’s(D25C Nichia 219A and D25A XM-L2 4300K NW) are effected too. I think it is more the reflector causing the problem though. I still like the lights overall, they are far from the worst light purchase I have made. Hopefully they will use the new AR coating and different reflector designs on all models going forward. They are one of the only (non-budget)companies using descent emitters these days. I particularly like that they now offer the 219C SW40 R9050 in some models.
Just did some tests again as I remembered I had figured out it wasn’t the lens on the D25’s causing the problem. It is definitely not the AR coating, it is the reflector design. I think this is the case on many lights. The AR coating isn’t always the issue(although it can be), it is the reflector. It could be the geometry of it or the reflective coating used, I’m not sure. Maybe this is why the D4 doesn’t have this issue? It doesn’t use a reflector.
Agreed on the quality of Klarus’ AR coating. I have a Klarus XT12S, and while the tint isn’t my favorite (Klarus, why no NW options???) there is basically zero visible tint shift.
Tachead, the UCL comes in a small set of sizes. Most of our lights there just isn’t a choice, it’s UCLp or nothing. Like the 104mm I recently special ordered from Chris…. 
I’ve heard that the reflector can cause tint issues, but I’ve never actually seen it happen. I suspect it’s a different type of tint issue. Like, a combination of emitter and reflector can produce sort of a rainbow beam where different areas have different shades. I usually refer to this as the Cree rainbow, since it’s significantly more noticeable on Cree emitters (especially the most recent ones like XP-G3). It also tends to make the center of the hotspot yellow with XP-L HI emitters. This type of issue can usually be resolved or at least reduced by switching to an emitter where the output doesn’t change as much with emission angle.
What I see from AR coating is usually two things:
- The beam (especially hotspot) gets warmer and greener.
- The edge of the spill gets a blue halo.
The two types of issues are independent of each other. It’s possible to have a rainbow beam and a blue halo plus green hotspot.
In the case of the EagleTac (and the Olight and the Q8 and every other light I’ve tried), I managed to remove the lens… and the tint issues disappeared.
I don’t have a solution for rainbow beam issues, at least not without significantly changing the beam in other ways too. Putting a diffusion film on the lens can fix it, or using a textured reflector, or sometimes using a different brand / type of emitter.
Right, I forgot Chris only does the custom sizes in UCLp.
On my latest mod, my own DBC-05, I put a new reflector from KaiDomain with new XHP-70.2’s in it. I can see a blue reflection in the reflector when the light is in lower modes. This is one you definitely don’t want to look at in higher modes! But without a doubt the blue color is bouncing back from the AR lens, ya gotta have a lens over it though, and with a custom build sometimes glass lenses aren’t readily available. It does make me wonder how it’d perform without the AR, or glass at all for that matter. Not in a hurry to take it back apart and see if there are more lumens to be found, it’s only 60 away from 19,000 as it is!
I could test my SupFire M6 and a Q8 with and without lenses, see what the light box says… do I really want to know how much I’m losing to a lens that still has to be there? Wonder if there’s a source for high quality Schott Glass to have custom sizes cut?
I just did a test on my D25C Nichia 219A. Try it on yours. Take out the reflector and the blue halo goes away. Add the lens back but, leave out the reflector and still no blue halo. It seems to be the reflector combined with the lens that makes it the worst.
I also just tried the lens in front of a 219B 4000K and all it does is ever so slightly warm the tint. No blue or any colour added what so ever.
Tachead,
Try with the reflector but without the lens…no more blue halo, right ?
Thanks for the info/pics TK, Tac and Dale appreciated . So its not witch craft after all(or me going mad) 
Light travels from the emitter to the reflector, then collimates forward to the lens. Normally, about 5-10% would bounce back, but the AR coating changes that by allowing more light to go through — specifically more green light. Blue and red shades still mostly bounce back normally. The red+blue then hits the reflector again and bounces out at a different angle, causing a blue or purple halo.
This doesn’t mean there’s anything wrong with the reflector. It’s a side effect of how the AR coating selectively passes some frequencies more easily than others, and how it changes its response based on angle of incidence.
The effect isn’t very noticeable without a reflector because the light isn’t collimated, reflected light absorbs into the host instead of going out the front, and a bare emitter generally doesn’t have any sharp edges in its beam.
The AR coating is a bandpass filter, and the reflector bounces the band-rejected parts of the beam back out at a different angle instead of letting that light be absorbed by the host.
Yes, that’s how it looks when the AR bandpass filter is active but the rejected frequencies don’t make it out the front of the light. Slightly warmer, slightly greener, and no visible blue or purple area. The blue gets converted to heat inside the host instead of showing up as part of the beam.
Yeah, I did that too. Then the blue halo is added to the spill and not redirected to a halo. The reflector seams to be separating the blue spectrum from the emitter and putting it into the spill. The lens just redirects part of the blue spill into a halo it seems. Maybe that is the light that is reflecting off the lens instead of passing through? Maybe the lens only reflects the blue spectrum due to the AR coating used? I think that is what it is because if I shine light off the lens it casts a blue reflection. Either way, if you remove the reflector the beam is uniform with or without the lens. No more blue spill and no more blue halo. So, maybe its a poor reflector design and a poor AR coating working in conjunction lol. I don’t have another lens this size to try to see if that makes a difference. The bottom line is, this Eagletac has a crappy beam :confounded: .
Sorry for the huge derail people lol.
Cree emitters tend to emit different color temperatures at different angles. The spill is composed of light which was emitted forward (or close to forward), while the hotspot is made of light which went sideways into the reflector. This is why the hotspot is almost always a different color temperature than the spill. It’s not due to the reflector separating the blue spectrum; it’s due to the emitter emitting different frequencies at different angles. I mean, there will be some chromatic aberration from the reflector, but it’s typically a small fraction of a degree… not the 30-degree splits we see in flashlight beams.
Usually the LED’s colder wavelengths are emitted forward (into the spill area) while warmer wavelengths are emitted sideways (into the reflector and hotspot). Borrowing some pictures from maukka…
That happens without a lens. It even happens without a reflector, though it’s harder to see since the change is gradual… and without a reflector, it’ll be cold in the middle instead of warm. But with an AR lens, additional factors come into play. Not only does the lens reflectivity vary by wavelength, but the entire curve also shifts with angle of incidence. This is how antireflective coating performance looks on a graph:
At an angle of 0 degrees (red curve, hitting the glass straight-on), the green middle wavelengths pass through more easily while red and blue (especially blue) are more likely to reflect back. It then bounces off the reflector again to hit the lens at a different angle, like 40 or 50 degrees. But at that angle, the blue passes much more easily and it goes out the front of the light.
This is how it looks from the outside, in the area where the blue halo comes out.
The light path is something like this (apologies for the terrible diagram):
Without AR coating, some (even more) of the light still bounces around but it doesn’t get split by color so the re-reflected light still looks white.
And this will all change with different AR coatings.
Yup. There’s a whole niche of research and engineering devoted to finding the best antireflective materials for various purposes. Some want a very narrow bandpass and don’t care about angle of incidence, like lasers. Some want a wide and flat bandpass without angle sensitivity, like in flashlights. Wide and flat is hard to do though.
The info above is mostly about the stereotypical blue-ish AR coating used on a lot of flashlights.
I’ll have to look into it more, but whatever Hank used on the D1S seems to have opposite behavior… I think it might let cooler frequencies pass at 0 degrees while letting warmer frequencies pass at 45 degrees, which kind of cancels out the Cree rainbow effect. It makes a nice-looking beam.
You can send that D1s over here and I’ll check it out, see what’s going on with it. 
D1S??? You wouldn’t happen to know someone with a review in progress….
Hmmmmmm. The anticipation 
Are there any plan for a 26650 based D4?
It would look a lot like a DQG Tiny 26650… with likely twice the output - like a mini Q8.
With a 26350 tube it would look quite fat though…
26650 twice the output, how you that be possible? 26650 are not double of 18650 in power.
You think with a 26650 you will have 150W (double of 75W) of output in an ultra tiny body?