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Point of Equal Energy represent achromatic light, but is itneutral?

R

Roger Breton

At x=0.333 and y=0.333 is the point of equal energy, with a correlated color
temperature of 5470 degree Kelvin. Is this point really 'achromatic' for the
1931 Standard Observer? Can you say that a light of this chromaticity
largely evokes an achromatic sensation in the brain? And does that color of
light bear any relationship, physically, with solar light?

Roger Breton
 
J

Jacek Zagaja

At x=0.333 and y=0.333 is the point ... Is this point really
'achromatic' for the 1931 Standard Observer?

Good question! May I ask from mine ?

- Two light sources CIE E and A evaluated in the same time in field of
view by standard observer. E Illuminant will be seen as blue as D
Illuminant then? It is possble to build a solution filter (for E from
A (I've found for B nad C)?

Stay well -- Jack.
 
R

Roger Breton

Gernot,
both D65 and D50 are not on the curve for the Planck radiator,
they are slightly above.
EE is slightly below, roughly between D50 and D65.
http://www.fho-emden.de/~hoffmann/coltemp18102003.pdf

Therefore I guess that EE would look neutral, like D50 or D65,
if shown isolated.
A CONVERSION of a D65 image to EE, shown on a D65 monitor,
would produce a clearly visible shift.

Fig.2(1.2.1) in Wyszecki&Stiles shows that the curve for vary-
ing daylight doesn´t pass the EE point.

Best regards --Gernot Hoffmann

I guess the EE point is just an artificial theoretical construct, then, if
it does not have some kind of physical correlate?

Is it just out of Plank's Blackbody Locus? Something you calculate with
temperature of a blackbody?

Anyone ever constructed an EE real source? Probably not. How frustrating is
this CIE system of abstractions where you're asked to believe, blindly, in
some mathematical dogmas...

Mit freudlichen grußen,

Roger Breton
 
T

TKM

Roger Breton said:
Gernot,


I guess the EE point is just an artificial theoretical construct, then, if
it does not have some kind of physical correlate?

Is it just out of Plank's Blackbody Locus? Something you calculate with
temperature of a blackbody?

Anyone ever constructed an EE real source? Probably not. How frustrating is
this CIE system of abstractions where you're asked to believe, blindly, in
some mathematical dogmas...

Mit freudlichen grußen,

Roger Breton

Feel free to invent something better. We certainly need it in the color
area of lighting :)

There's no particular significance visually to the EE point and since it's
off the black body curve, it's not likely that nature will provide us with
such light.

Terry McGowan
 
R

Roger Breton

Feel free to invent something better. We certainly need it in the color
area of lighting :)

Well, I'd like to. But I don't have enough electrical, physical and material
knowledge.
There's no particular significance visually to the EE point

Ah! Thank you. That's what I was after, whether there was any visual
significance to it. I understand now its significance is purely
mathematical. In wonder what Dean Judd would have to say it, if he ever
wrote a passage about its significance at all?
  and since it's
off the black body curve, it's not likely that nature will provide us with
such light.

Terry McGowan

I realize now that the EE point plots below the blackbody curve. Thank you.
Still, that does not quench my conceptual curiosity. I sense, perhaps
naively, that the EE could have some theoretical value beyond a simple
geometrical by-product of normalizing XYZ to zyz? Perhaps there is a
relationship between EE and the sensation of white in our brain? That's my
naïve intuition.

What bugs me, conceptually, is the idea of 'white' as a sensation, an
empfindung. I guess there is no such thing as 'absolute white', white as an
achromatic color is always *relative*, always a function of our state of
adaptation and the surrounding field (perhaps an oversimplification?). Maybe
what I'd need to do is to research the field of physchophysics to see what
research, if any, were ever done on the 'impression of white', especially in
relation with correlated color temperature or the blacbody locus, if such
thing is possible. My hypothesis is that, yes, there is a relationship
between the two. And it is be based on the quality of natural sun light. My
view is that the SPD of the direct sunlight is what I believe we're all
fundamentally adapted to, after zillion of years bathing in it, and this
quality of light has long passed into our "collective unconscious" to become
our reference for white sensation -- nothing else in nature comes close to
replicating the quality of direct sunlight for sheer white impression
(that's probably what makes it so difficult, industrially, to reproduce it).

Now, I remember reading on this list someone saying that this type of light
was slighthly yellowish in appearance. OK. Does that mean that, for normal
adaptation, the brain accepts this illuminant as our 'reference white' --
regardless of where we are on the earth? I know we discount the illuminant
but off all the illuminant we could be discounting for would one closest to
EE be the one we would be discounting 'the least' for? Because it would be
closest to, what, natural direct sunlight?

I'd be curious what Albert Munsell thouth about the quality of direct
sunlight for sheer colourfulness power (thank you Bob Hunt)? To anyone's
knowledge, has he ever written about anything than his system?

Maybe I ought to find a physchophysics newsgroup. Is there one?

Regards,

Roger Breton
 
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