I have to agree with Jim Kasson on this one...
Maybe. Keep in mind that any Kelvin value is a range of colors. D65 is a specific color, 6500K is a range. The type of lighting too can play a huge role. A 6500K Fluorescent with the spiky spectrum may produce a vastly different color appearance than a Solux with a similar spec for Kelvin. Add OBA's into the mix, you'll soon find that such values are not really useful. Getting a screen to print match is and often, differing values end up producing this goal.
Perhaps you misstated yourself. Techno-geek Warning
* Skip this section if you aren't into technical discussions, you won't miss any real-world information!
Since you are wanting to be SO specific, both D50 and 5000K refer to spectrums of visible light. D50 is part of the Standard Illuminant series D standard. It is, "A standard illuminant (which) is a theoretical source of visible light
with a profile (its spectral power distribution
) which is published
" (emphasis mine)(1).
I can see how someone can confuse D50 as being a specific color because of the chart below:
The D65, D50, etc. "spots" on the CIE X,Y "horse shoe" is a transformation of a spectrum power distribution (SPD) (from ~300-700nm, the visible light spectrum) to a specific point in the CIE XY color space "horse shoe"(2).
For all practical purposes, saying that D50 and 5000K (for print) are equivalent is essentially correct due to the nature of their SPD's being almost a match. In fact, in the Wikipedia article on Illuminant D65(3) it says:
"As any standard illuminant is represented as a table of averaged
spectrophotometric data, any light source which statistically has
the same relative spectral power distribution (SPD) can be considered
a D65 light source. There are no actual D65 light sources, only
"[D65] is intended to represent average daylight and has a correlated colour temperature
of approximately 6500 K."
You can see the relationship between different series D Illuminants and their relative black body correlated color temperatures (from 4000K to 25000K) in the chart below:
Because of this, D50 and 5000K are essentially (statistically) the same. I want to repeat that while there are D50 and 5000K "dots" on the CIE XY horse shoe, which appear as specific "colors", these values represent a transform of SPD's of light colors (wavelengths) to force it to fit into a two dimensional, XY, diagram and it is only the spectrum of colors that creates "white" because "white" is NOT a color frequency (like it is implied in the CIE XY diagram), it is a combination of colors (i.e. a spectrum of colors).
This is why they call 5000K a "correlated color temperature" to D50. Frankly, trying to match spectrums is a rather overwhelming and confusing idea to most non technicians, as opposed to "only" have to match a specific color temperature, even if that color temperature does imply a matching spectrum.
Functionally, this means that any 5000K light source will work as a viewing source for proofing prints!SoLux
* You can skip this section if you are more interested in real world light booths...
No pre-press or print shops I have seen or know of use any type of incandescent light source. Not even something like the SoLux 3500K, 4100K, or 4700K halogen light source.
While I have perused the SoLux web site and see they are big with art galleries/museums, we need to keep in mind that art galleries are far different than print shops.
By definition, art galleries are interested in (1) presenting an artistic
representation of something (e.g. the artistic representation might be a painting) and (2) protecting that representation from potential damage (e.g. from lighting sources). So while SoLux's products may be very appropriate for viewing original art, that is very different from accurate (and consistent between locations) reproduction of reflective source materials (and their relative spectral power distributions) and avoiding metamerismic errors in reproduction
that, for example, pre-press and print shops must do.
As a practical matter, to get even lighting, you would have to have a number of incandescent lights to cover any reasonable light booth area and they produce A LOT of heat. Many pre-press viewing booths are on press floors which are not air conditioned. Because of this, many get VERY hot during the summer months and an incandescent light booth (effectively a heating oven with ~90% of its energy being converted to heat) would be impractical.
While early florescent lights did have some nasty "spiky spectrums" (the infamous "green cast" problem), this is much less of an issue now. Even over the last 10 years, manufacturers have gotten much better at matching the necessary phosphors to get a usable spectrum of light at any particular color temperature. Practically, this means that a Home Depot 5000K florescent bulb, a specialty "full spectrum" florescent bulb, and the $5000+ Xrite SpectraLight III lighting booth will produce the same results.
Also, SoLux's emphasis is on CRI accuracy, which may or may not accurately represent the relative spectral power distributions of a printed proof or its source standard, D50. As Jim mentioned, there are many metamers of the Illuminant series D standards as represented in the CIE XY diagram, but only one that is used as the correct SPD in the D50 standard. Depending on the SPD of these alternative spectrums they may or may not be practically different.
Also, you shouldn't confuse Color Rendering Index (CRI), which is based on Illuminant series F lighting values(1) with equivalents to Illuminant series D SPD values.In The Real World***** This is the section you should pay attention to if you want to duplicate what pre-press (including magazines and newspapers) and print shops (even ad agencies) are using in the real world!
In the real world, pre-press and prints shops where they are comparing the press prints vs. the digital proofs (95+%) is done with 5000K florescent lights in a viewing box. 5000K florescent lights are the standard.
Because of this, even if the SoLux (and other) lights were "more accurate" SPD representations, they will still be different than what is used in the vast majority of lighting booths (and transparency light tables)... 5000K florescent lights. You can verify this for yourself by visiting a few local print shops to see what they are using. There is likely far more of a difference between a halogen 4700K (300 degrees Kelvin off the standard) light source and a super high quality light booth (e.g. Xrite SpectraLight III at $5000+(5),(6)) than there is between a Home Depot 5000K florescent and that same light booth.
Even if there were no effective difference between the three, there are cost considerations that make florescent lighting the preferred choice (equipment and electrical).
It is both relatively easy and inexpensive to make your own print proofing light booth using florescent lighting. I would imagine that someone with some tools, time, and imagination could make a serviceable light booth with 2', 3', or 4' (depending on size of proofs) florescent light fixtures for <$250 (certainly less than $500). "All you need" is some plywood (box); 2x4's (legs and structure to nail the plywood to); reflective white (without coloration) siding and/or paint ("white" should reflect almost all of the light that hits it so just about any "pure white" should work); one or more two-bulb florescent fixtures; ; miscellaneous wiring, switch(es), nails, screws, etc.; and a bit of time.Back to the OP's initial questions/problem
Anyway, back to the OP's problem: How can he be sure that his customers will view his work in the way he intends them to?
First, which he already appears to have in hand, is to have a calibrated monitor which he uses to make any necessary adjustments so that his work meets his artistic/aesthetic requirements regarding appearance (assuming compositional issues were resolved at the time of taking the pictures).
Second, he needs to have a way to ensure that when his customers print his work so that what they see is substantially what he is seeing on his end. To that second end, I suggested (a) ensuring that he was viewing his printed results in a 5000K light booth/environment and (b) to send a copy of his printed proof along with the digital file so they can ensure that their printed and/or ripped/pre-press results match his proof. Because most print proof lighting booths use florescent lighting, it behooves him to use florescent lighting in his booth as well. Of course, I say "booth", when that may only mean an overhead florescent light fixture (two to four 2'-4' 5000K florescent bulbs) in a light controlled, white walled room.
The pre-press industry has been dealing with these issues for longer than you or I have and it is well known/understood how to set up a proper viewing environment, even on the cheap. Other Stuff
Frankly, I hadn't intended to get into this level of detail. I had thought people would not have started "picking fly manure out of the pepper" (you end up with all fly manure and no pepper) and used it as the basis for establishing how to properly go about setting up a viewing/proofing environment and/or workflow so the OP could ensure his customers saw his work as he did, especially if he doesn't have a photospectrometer. While theoretically interesting, this discussion probably doesn't help the OP with his goal.
Oh, an additional point. @digitaldog - You mentioned that, "Getting a screen to print match is and often, differing values end up producing this goal." The issue you are describing is one of metamerism of which lighting is only one component.
"The appearance of surface colors is defined by the product
of the spectral reflectance curve (paper/inks - Scott) of the
material and the spectral emittance curve of the light source
shining on it. As a result, the color of surfaces depends on
the light source used to illuminate them."(4)
Overcoming just the difference between emmissive light (monitor) and reflected light (print) can be difficult. From the sound of it though, letting Photoshop handle the color may be part of the problem, especially if he also has the OS/printer handling it (a "double whammy"), which could result in the over saturation problem he describes. One or the other probably need to be turned off, maybe even both.
Perhaps you can suggest a workflow that can help him with this process?
Finally, regarding why the original poster's pictures look more "washed out" on the web I can think of a couple reasons.
First, is the web browser color managed (I believe the latest version of Safari is)? Some are capable, but not all of those have color management turned on (Firefox).
Second, does he know that the destination is not recompressing them and/or doing additional processing that is changing its appearance. Even something as small as sharpening and/or recompression (to change the compression ratio) can have a detrimental effect on the appearance of photographs. I wonder if he has tried bringing those photos back into Photoshop to see if they still look washed out compared to the original? If so, the problem is on the other end. If not, then the problem is probably browser related.
If anyone has references that could correct a misunderstanding I have I would, sincerely, like to see those references!
(under Illuminant series D)