GTI Print Booth

[petercorb]

I am about to invest in a light booth for print to screen evaluation. I have always used D65 as a WP and have my screen luminance quite low at about 85. I work in a room painted neutral gray and use a single D50 fluorescent about 8 meters away for ambient light, the latter does not reflect in my screen at all.
Reading various experts related to this subject - as usual opinions vary.
Andrew Rodney: D65 or Native WP with a D50 light source in his personal GTI. Jeff Schewe D65 WP, D65 light booth: John Cone D50 WP and D50 GTI booth.
I have to import into South Africa so can't afford to make a mistake, if there is such a thing
Your advice would be appreciated.

[digitaldog]

I am about to invest in a light booth for print to screen evaluation. I have always used D65 as a WP and have my screen luminance quite low at about 85. I work in a room painted neutral gray and use a single D50 fluorescent about 8 meters away for ambient light, the latter does not reflect in my screen at all.
Reading various experts related to this subject - as usual opinions vary.
Andrew Rodney: D65 or Native WP with a D50 light source in his personal GTI. Jeff Schewe D65 WP, D65 light booth: John Cone D50 WP and D50 GTI booth.
I have to import into South Africa so can't afford to make a mistake, if there is such a thing
Your advice would be appreciated.

The number per se are meaningless! The only true D50 or D65 illuminant is 93 million miles away. These Standard Illuminants were produced by averaging measurements made world wide, over many months using different instruments. GTI booth's are great but they use Fluorescent bulbs and their spectrum isn't anything like daylight. Case in point is the spectrum of the GTI booth below.
Pick a viewing booth or make one based on your needs and don't worry about the number's specialization as you'll find YMMV and the calibration of the display white point to match may be numerically far different. Displays have differing backlight technology, as do the viewing booths. Solux and GTI have advantages and disadvantages. Solux has a much smoother spectrum but produce heat and are harder to control. GTI is great if you work with others using the same technology which is very common in prepress.

Andrew Rodney: D65 or Native WP with a D50 light source in his personal GTI.

That's my recommendation solely as a starting point, the values probably will not be the same for you. FWIW, my GTI booth at 80% matches my Luster prints with a white point of 5750K using a SpectraView PA272W which utilizes a GB-R LED and their software. The same booth with the same print might need a completely different setting if using a different display, say with a CCFL backlight. Your Mileage Will Vary!

[earlybird]

Is it true that ordinary incandescent lights have a CRI near 100?

[digitaldog]

Is it true that ordinary incandescent lights have a CRI near 100?

Don't know, could measure it in BableColor and produce a report but it doesn't really matter. CRI is a lousy metric!

[earlybird]

I do not know why you say that CRI is a lousy metric. I am not prepared to argue the point and I welcome an explanation of your perspective.

I can say that I have found that lighting with a better CRI rating seems to provide the most natural looking white balances when I adjust our electronic cameras to white balance. The professional "photography" grade florescent and LED instruments we use do not provide the same natural results that we get when white balancing with tungsten, HMI, or sunlight.

I know that CRI doesn't provide enough info with regards to selecting ideal lighting for prints and reflective light, but it does provide some clues as to why some lighting may be less than ideal for viewing anything critically. The low CRI rated light sources don't seem like great choices.

[howardm]

Not meaning to steal the thread but has any comparison been done between the GTI and the JustNormlicht booths?

[digitaldog]

I do not know why you say that CRI is a lousy metric. I am not prepared to argue the point and I welcome an explanation of your perspective.

Sure. CRI, it's a bit of a kludge to make a light source appear to be closer to daylight for marketing and light manufacturers. CRI was developed in large part to aid in the sales of Fluorescent tubes. The metric is produced using BCRA tiles to compare under a reference light source but only eight or there abouts. That's too small a set of tiles. That make it easy to create a spectrum that will render the 8-14 tiles and doesn't tell us that the light source is full spectrum. It doesn't tell us how the other colors will render. My understanding is there are two reference sources; Tungsten for warm bulbs and D50 for cool ones: Above and below 4000K. That means that a normal tungsten bulb and perfect daylight both have a CRI of 100! As such, a high CRI is a decent gauge of how well a light will preform in your home but not such a great indicator of how well it will work for photography and proofing. Both a Solux 48 and a "full spectrum" tube from Home Depot may have a CRI of 97. I can assure you the Home Depot bulb has a giant mercury spike and some spectral dead spots.

[digitaldog]

Not meaning to steal the thread but has any comparison been done between the GTI and the JustNormlicht booths?

I've got an old, portable JustNormlicht viewing box, I could measure it. But I suspect it is not really an apples to apples comprising to the GTI Soft-View I have.

[howardm]

Thanks for the offer but don't bother.

[Doug Gray]

If anyone wants to see the effect of fluorescent lighting on prints you can select an illuminant spectrum when making a profile then cross render the image.

Convert normally using RI or PI as preferred, then convert back using RI with the fluorescent illuminant profile. Use one of the spectrum standards or a spectrum capture if you don't have a matching standard .  The image will now look like the picture would appear under that fluorescent light.

Then just switch back and forth to see the effects. It can be pretty large. It's also a way to see how good a supposedly high CRI illuminant really is with your own print.

[Schewe]

Jeff Schewe D65 WP, D65 light booth

I needed ti change my bulbs and when ordering I got the D65 on a lark to test (I also got backup D50 bulbs). However, I found I got a better screen to print match with the D65 bulbs and using native WP for the displays. Note, I'm using the earler NECs. In the near future (when I upgrade may computers) I'll be replacing my NECs with the current line and I might end up changing my mind about native WB...

YMMV, there are no magic bullets...

[petercorb]

Interesting; the supplier here in SA pushed me yesterday to place my order before Christmas so I did what Mr. Schewe did, I ordered a D65 kit along with the standard D50 - about 12% extra, no brainer really!

I use a NEC PA272W-BK-SV (alongside my old Dell U2713H as a second screen) so it will be interesting to compare the two spectrums with my set-up.

"YMMV, there are no magic bullets..."

Of course not, every set-up is unique.

[earlybird]

It seems like a small HMI instrument would be an ideal choice for a light box.

[BradSmith]

Earlybird,
And what, might I ask, is an HMI instrument?

[earlybird]

Hi Brad,
 An HMI light (a.k.a. instrument) is an arc light commonly used as continuous lighting when daylight balance, even spectrum, and high efficiency is desired.

 They are expensive to purchase but the light quality is very nice.

 Here is an explanation: https://en.wikipedia.org/wiki/Hydrargyrum_medium-arc_iodide_lamp

 There are no florescent tubes, (regardless of stated CRI) that even come close in terms of even color rendition.

 We regularly use such lights for motion picture and photographic work. Now that I am learning about how seriously print makers take the lighting that they use when reviewing a print it seems to me that HMI lighting (with a protective UV filter) is an excellent candidate for the task.

 The downside is that the price is many times as expensive compared to all the other options.

[Schewe]

It seems like a small HMI instrument would be an ideal choice for a light box.

Not really...HMI's are notorious for sub-optimal spectral responses. Yes, in general, one can correct for the imbalances but HMIs are not a magic bullet. Do you really want to spend that much money to get a viewing light that is rather tweaky or do you want to get a viewing environment that provides meaningful representations like the GTI? (guess what my answer would be–get the GTI, not an HMI for print viewing).

[petercorb]

Some further information regarding my original post.

On the very last page of "Real World - Color Managemenot" - which I am sure you have all read cover to cover... There is a GATF RHEM light indicator. This small removable pink/purple-ish patch is printed with two inks that produce a metameric match under D50 light.

The author tells us that different D50 simulators have different spectra and that some may cause slight striping when the patch is viewed under such various simulators. The latter (the author tells us) is normally not a concern but if obvious stripes are visible then your lighting isn't suitable for critical color work - quite an emphatic statement for such a simple test !

I took my patch to my printing room and viewed it under my "so-called" D50 lights which is my working and print evaluation lighting and the stripes are very slightly visible.

It will be interesting to view the patch when I get my GTI and compare D50 and D65.

Has anyone used this patch or have any experience using this patch?

[Dale Villeponteaux]

Further re: "I do not know why you say that CRI is a lousy metric. I am not prepared to argue the point and I welcome an explanation of your perspective."

From an older thread: http://www.olino.org/us/articles/2015/03/07/color-quality-scale-cqs-measuring-the-color-quality-of-light-sources

Regards,
Dale

[earlybird]

Further re: "I do not know why you say that CRI is a lousy metric. I am not prepared to argue the point and I welcome an explanation of your perspective."

From an older thread: http://www.olino.org/us/articles/2015/03/07/color-quality-scale-cqs-measuring-the-color-quality-of-light-sources

Regards,
Dale

Yes, I haven't thought much about how manufacturers can manipulate light output to achieve high CRI ratings for marketing purposes.

I have previously thought about how CRI info is useful to gaffers who want to avoid, or recommend avoiding, bad lighting. After reading the articles, I can appreciate that my habit of regarding photographic grade fluorescent lighting, which is often rated at CRI 95, as mis-rated has probably been mistaken. Now I understand that fluorescent lighting can be both accurately rated at CRI 95 and be bad lighting at the same time.

[earlybird]

Not really...HMI's are notorious for sub-optimal spectral responses. Yes, in general, one can correct for the imbalances but HMIs are not a magic bullet. Do you really want to spend that much money to get a viewing light that is rather tweaky or do you want to get a viewing environment that provides meaningful representations like the GTI? (guess what my answer would be–get the GTI, not an HMI for print viewing).

How about Xenon?