Ah ha! It’s actually a Locus that merges the BBL and the Daylight Locus. Very cool. It does so by using the 5000k-4000k region to transition.
But… WHY? If the Daylight Locus is more green than the BBL, what is the supposed advantage of “merging” them this way? To say it another way: What light source is anyone measuring that they’d want to skew the “results” in this way?
Are you seriously complaining about the color of daylight? The advantages are numerous for technical and non-technical reasons. We evolved under daylight. We want our lighting to agree with daylight. Not have some weird discrepancy.
I understand that our eyes are naturally matched to daylight. But, why merge the lines? What advantage is it in scientific testing of “fluorescent” lights, including LEDs? The two lines exist already, and can be measured against, so what does this add that we need?
EDIT: BTW, I’m not complaining about daylight. That would be silly! 
I love these new below BBL LEDs for photography!!!
Again, studies pretty clearly demonstrate we don’t want that. It’s extremely useful to have a proper daylight reference in many situations, but it doesn’t mean it’s what people want for general lighting, especially at night. User preference is much more important than achieving the one true neutral tint.
Ain’t that the truth. Looks just like a 219B SW45K to me 
I think you are confusing rosy with warm. Warm light is awesome at night. But it’s still neutral.
If what Bob said doesn’t make sense, you may be confused. But this is not a bad thing. Being confused can be a very useful thing, if one is able to recognize it.
One day, students went into their physics class and the teacher showed them a large thick metal plate with one end very close to a fire and the other end a couple meters away. The teacher instructed the students to feel the metal plate, and they felt that the end near the fire was cooler while the end away from the fire was warmer. So the teacher asked the students to write down a guess about why.
Some students wrote things like “because of how metal conducts heat” or “because of how air moves”, but no one wrote “this doesn’t make sense” or “this seems impossible”. So no one got the right answer… which was that, just before the students came into the room, the teacher had turned the plate around.
The students failed because they did not notice their confusion, and thus ignored the most important clue they had.
Usually, when one is confused, it means that one has a false belief or a false assumption. The sensible way to respond to confusion is by trying to identify what that false belief is… and get rid of it.
In this case, I think the confusion may be caused by the false belief that humans in general want artificial lighting to be identical to daylight (or at least on the blackbody line). The available data on this topic indicates that most people actually do not want this, and instead prefer something a bit more rosy in tint. A perfect blackbody radiator may be ideal in a mathematical sense, but that does not mean it produces an ideal lighting spectrum for human use.
Or perhaps the confusion may be caused by the false assumption that Bob doesn’t know what he’s talking about. But he does, and he’s not confusing duv with CCT.
You are know TK, I’m getting tired of you deleting the relevant parts of my quotes to make me look confused. Let me quote that properly for you to read again.
Arguing opinions with opinionated people, why bother. Different people have different preferences regardless of if one is talking about CCT or Duv. Are these studies more than just surveys anyways?
My apologies. I may have left out another important bit too, and should quote it in case it was missed earlier.
It’s an interesting study, and I recommend reading the entire thing since it’s written in a very accessible manner compared to most research results. The findings are summed up pretty well below though:
Yes. People on average seem to find true daylight less preferable than a slightly rosy alternative.
In cases where there is no ambient light from the sun, like a flashlight in a dark house, yea I would believe most people prefer BBL to daylight if that’s what the studies/surveys say. But for the majority of use cases there will be daylight bleeding into the artificial lighting. Like street lights experience. Or houses with windows. Or security lighting. And when you have a BBL based light in one area, and it shifts into a daylight based light (the sun) weirdness happens. Sure, that weirdness goes away when the sun completely sets. But is it worth it? Who cares, because it is just a locus, and you can still have personal preference.
Before commenting any further, everyone should read this article carefully. It explains the NIST and other research into colour perception and preference TK and I are discussing and how it has influenced ANSI colour standards. Not only were very negative Duvs strongly preferred at all CCTs by most test subjects, but the cutoff for even perceiving a tint as white is also much lower at 4000K and below. For most people, a perfectly neutral Duv is not preferable after becoming accustomed to the light source. That doesn’t mean there shouldn’t be any neutral lighting, or that a daylight reference isn’t useful, but user preference is ultimately what matters.
I think we posted at the same time Bob_McBob. Yea I could believe that your vision could shift that far in a completely dark room. But daylight blends in from everywhere in our daily lives.
These two experiments on 18 and 21 people appear to just be a way of requesting further funding and research for a more comprehensive study. While I don’t doubt people prefer negative Duv (to what extent who knows) this article is far from gospel and highlights that people like TK are still “not average” and apparently neither are people who prefer something closer to the BBL.
I understand that it can be frustrating when things don’t quite line up. Humans evolved on this planet, so human vision should be perfectly aligned with this planet’s natural light source. But it’s not… and that’s okay. Almost nothing ever lines up perfectly. The universe is an incomprehensibly vast gallery of slightly-tilted paintings.
In the past, I’ve asked many non flashlight folks to get their opinion on which beam color they prefer the most. If the CCT is about the same, EVERYONE ALWAYS say they like the below BBL tint more than On the BBL and they dislike the above BBL tint. Sunlight is above the BBL and to me only looks great only when the intensity is high and does not look good when only a faint amount of daylight gets in the house. However, no flashlight can achieve lumen output anywhere close to sunlight so for most cases during night time, I can confidently say the majority will prefer negative duv.
My ideal is slightly rosy with DUV between –0.002 to –0.005. 219B SW45K measures –0.01x on turbo, which is a bit too pink but I still prefer it over a positive BBL. In fact everyone I showed my 219B sw45k flashlights to like the tint better than any on or above bbl 4000K-5000K flashlights.
Why, exactly, are we invoking merely statistical studies here, especially ones with all of sixteen people as subjects? If these studies are meaningful, it is to lighting marketers, not consumers. As the researchers clearly point out, “Color preference or perceived color is subjective. It depends on the light level, the surrounding environment, or even the observer’s cultural background.” So in what way are preference statistics relevant to what you or I like, or to the relative chromaticity merits of the SST-20 versus the 219B (which is how this discussion started)?
Edited to remove my own confusion between “perceived whiteness” and “preferrred tint.”
Ok I stepped away to take some pics.
If we light the right side with “daylight” and the left with rosy, our eyes need to pick a white balance. They pick daylight, and make the left side red-tinted.
Now if our brain sees the rosy side as white, but there is daylight too, the daylight looks green. And again this is weird.
But if we have matching light sources, there is only one white point and all is white.
So unless you can eliminate the daylight from the sky, you are forced to agree with it.
And yes, if you do eliminate the daylight, there is a preference for a rosy lights, but you don’t really notice it’s rosy after you adjust.