LCR study concludes untinted white is not on the BlackBody locus

Kinnza · Apr 14, 2012

Dr Freyssinier from Lighting Research Center (LCR) of Rensselaer Polytechnic Institute presented at SIL 2012 the last experiment covering tint perception along all CCTs, a long needed study. Although results has been in the past suspected by experts, this is the first time it is empirically confirmed on a scientific study:

"Pure White" perceived by people, meaning light has no tint (hue), is not on the blackbody locus nor daylight phases locus (although the latter is closer and almost exact from 4100 to 5000K).

The study was performed with 20 persons (likely, more color research groups will replicate it soon) and found that when presented a white stand illuminated with 7 lights for each CCT (6 in total), answers clearly pointed out they perceive as untinted white not lights with chromaticities off the planckian locus.

For the three cooler CCTs analyzed, 6500K, 5000K and 4100K, untinted white was perceived over the BB locus, thus for people the BB locus has a purple tint at these CCTs. Not huge, untinted white selected was always the first option over the BB locus (the closer to it, but BB itself was perceived as tinted).

But for the 3 warmer CCTs (3500K, 3000K and 2700K), untinted white was perceived below the BB locus, meaning BB locus is perceived as with a green tint. So really, using BB locus or, in the practice, incandescents, as reference for untinted white has no any support, and poses and interesting dilemma about references used for color rendering metrics.

The page at LCR explaining it, with more links at the bottom: http://www.lrc.rpi.edu/programs/solidstate/assist/whitelight.asp

This is the presentation used at SIL: http://www.lrc.rpi.edu/programs/solidstate/assist/pdf/SIL-2012_FreyssinierRea_WhiteLighting.pdf

And LEDs magazine article talking about this at SIL 2012 report

Optical Inferno · Apr 18, 2012

Just noticed that in the first link on the second image on the right it mentions nothing about LED as a light source. The lines on the graph appear to be for linear fluorescent and CFL only, with the last being an all intensities.

Also...20 people means it is still very subjective. Not too sure how to go at this though...

eh4 · Oct 21, 2012

It's over my head, but based upon what I think that I understand my rule of thumb is: If there are more lumens than needed they should be tinted towards blue (say 4000+ Kelvin) while if I want to see well with a "dim" light I'm going to want a light tinted towards red (say 4000-Kelvin). And though I don't care for the tint of the mono chrome light one bit I accept the idea that if i want to see with as little light as possible then the light needs to be around 550nM "night vision" green.
Since it's more complicated and expensive to have more light than needed I tend to focus on the lower than 4000K high color rendering leds.

Btw, with minimal lumens, red still seems to give the best center of vision fine detail, another point in favor for red leaning neutral and High CRI tints, at least for small edc type lights, assuming that you will want to see details more often than maximizing peripheral threshold impulses -I think that I understand that blue/green light wins in the periphery department.
IE, Red leaning tint for maximum detail vision in center of focus, Green leaning tint for maximum shape/movement/object detection outside of center of vision -out to the very corners of your vision, and Blue tint for maximum possible lumens per watt due to the physics of led technology.

SemiMan · Oct 21, 2012

eh4 said:
It's over my head, but based upon what I think that I understand my rule of thumb is: If there are more lumens than needed they should be tinted towards blue (say 4000+ Kelvin) while if I want to see well with a "dim" light I'm going to want a light tinted towards red (say 4000-Kelvin). And though I don't care for the tint of the mono chrome light one bit I accept the idea that if i want to see with as little light as possible then the light needs to be around 550nM "night vision" green.
Since it's more complicated and expensive to have more light than needed I tend to focus on the lower than 4000K high color rendering leds.

Btw, with minimal lumens, red still seems to give the best center of vision fine detail, another point in favor for red leaning neutral and High CRI tints, at least for small edc type lights, assuming that you will want to see details more often than maximizing peripheral threshold impulses -I think that I understand that blue/green light wins in the periphery department.
IE, Red leaning tint for maximum detail vision in center of focus, Green leaning tint for maximum shape/movement/object detection outside of center of vision -out to the very corners of your vision, and Blue tint for maximum possible lumens per watt due to the physics of led technology.

Interesting article. This would explain some of the earlier studies where lower CRI LED lights were picked as preferable to incandescent high CRI sources.

That said, some of the articles talk about "preferred" but I think what they really mean is perceived as white. There is a difference.

This article could explain why I really like high CRI 4000K sources. I have a 95+ CRI 4K source. There is something really nice about it.

Semiman

THE_dAY · Oct 21, 2012

Just a thought and I don't know if this is related to the article,

I know my perception of white changes with what time of day it is.
I have different display profile settings on my laptop and will prefer the warmer settings at night.

What might look like a white screen in the morning can look too cold in the evening so I change to a warmer setting.
Then in the day the screen will look too warm and I'll change it to a cooler setting.

I wonder what was the weather like before these people walked into the study, (cold cloudy skies or a warm golden evening)?

anuragwap · Oct 30, 2012

Deleted!

AnAppleSnail · Oct 31, 2012

It seems obvious to me, since we've lived our whole history under a filtered light source, that black-body ain't the last word in lighting. Neither is CRI the last word in color rendering, since it explicitly states comparisons to black body radiators. At least CCT & CRI give one almost enough info...

LCR study concludes untinted white is not on the BlackBody locus

Kinnza

Enlightened

Optical Inferno

Enlightened

eh4

Flashlight Enthusiast

SemiMan

Banned

THE_dAY

Flashlight Enthusiast

anuragwap

Newly Enlightened

AnAppleSnail

Flashlight Enthusiast

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