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Author Topic: Determining viewing light brightness for print  (Read 1169 times)

Harry Lime

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Determining viewing light brightness for print
« on: April 19, 2021, 01:56:07 pm »

I have just set up my Piezo Pro system and am looking for some documentation that explains how to determine the brightness of a viewing light to review prints and matches my monitor calibration.

I am on a calibrated NEC MultiSync PA271Q set to AdobeRGB @ 85 cd/m2 / 5000k with the associated Spectraview software and probe in a dim room.

I may be able to get hold of an old GTI booth that is missing the light source. I plan on replacing the florescent with a dimmable LED light (diffused) that has a very high level of color accuracy and can be set to 5000k (cinema production light). I also have a calibrated Sekonic light meter than can measure lux, foot-candles etc.

Can someone please explain to me how this works or point me to some documentation that explains the process?

thanks in advance.
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digitaldog

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Re: Determining viewing light brightness for print
« Reply #1 on: April 19, 2021, 02:02:04 pm »

Why are my prints too dark?
A video update to a written piece on subject from 2013
In this 24 minute video, I'll cover:

Are your prints really too dark?
Display calibration and WYSIWYG
Proper print viewing conditions
Trouble shooting to get a match
Avoiding kludges that don't solve the problem

High resolution: http://digitaldog.net/files/Why_are_my_prints_too_dark.mp4
Low resolution: https://youtu.be/iS6sjZmxjY4
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #2 on: April 19, 2021, 02:08:07 pm »

Thanks, I'll have to give that a look.
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #3 on: April 19, 2021, 07:39:32 pm »

Hey Andrew

I watched your video and is very useful and explains the process clearly.

But I am still left with one question. How did you arrive at the 80% brightness setting for your GTI booth to match the LCD?

Knowing that your LCD was set to 150cd/m2 did you calculate a lux or foot candle value that you were able to reach with the GTI set to 80%

Did you just eyeball it? (which I somehow doubt given your level of expertise...)
;-)

thanks
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digitaldog

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Re: Determining viewing light brightness for print
« Reply #4 on: April 19, 2021, 07:42:02 pm »

Nope; eyeballs. Nothing wrong with that approach.
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #5 on: April 19, 2021, 08:43:00 pm »

Eyeballs it is.

Let me see if I can get this work....


Thanks
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Doug Gray

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Re: Determining viewing light brightness for print
« Reply #6 on: April 20, 2021, 01:19:46 am »

Knowing that your LCD was set to 150cd/m2 did you calculate a lux or foot candle value that you were able to reach with the GTI set to 80%

As Andrew said, this is most easily done with eyeballs. But for nerd interest, the relationship between Lux and cd/m^2 is Pi. That is, a light source that is 500 Lux directly opposite a perfect, white paper produces the equivalent of a  500/Pi or 159 cd/m^2. But papers aren't perfectly white. A good matte paper might reflect 90% of the light hitting it. Which is why, if you have such a near perfect setup and a monitor at 159 cd/m^2, when you select "show paper white" in Photoshop's soft proof, you get a brightness decrease because the paper appears to be 143 cd/m^2.

The other major complication is getting the monitor's white point chromaticity to match the hard proof light. A good profiling package will allow you to match chromaticity.
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #7 on: April 22, 2021, 10:41:16 pm »

So, here is a question.

I got my light setup and dialed in so that 500 lux, as measured by my Sekonic incident meter, are falling on the print. That visually matches my calibrated NEC MultiSync PA271Q set to AdobeRGB @ 85 cd/m2 / 5000k  very closely. (with soft proof turned on in PS)


Now here is a question.

I got my light setup and dialed in.

I have 500 lux falling on my print in my booth (as measured by my Sekonic incident meter)
That visually matches my calibrated NEC MultiSync PA271Q set to AdobeRGB @ 85 cd/m2 / 5000k very closely. (with soft proof turned on in PS)

Now here is an interesting observation.

It turns out that a reading of 500 lux (incident) falling on my print is the equivalent of shooting Tri-X @ 400 and 1/60 f2.8. That is the same exposure setting I have noticed in many museums around he world, like the Getty Center etc. It also happens to be the average illumination level I have encountered in pretty much every commercial office building, store or mall I have been in.

This brings up an interesting point.

So, now I have the monitor and review light (booth) matching.

But how does that light level of 500 lux compare to common light levels in the real world?

If we use a museum etc as a baseline and they mostly operate under the 500 lux rule, then my print would look as expected, when viewed under those lighting conditions.

I wonder if galleries strive for a similar level of illumination?
Is 500 lux (incident) an architectural standard for your average interior lighting level?

There may be something to that because over the years I have noticed that exposing at 400asa and 1/60th @ 2.8 is a very common light level in many commercial buildings, stores, offices etc. That is the equivalent of 500 lux.

The print and monitor matching is one thing. But it almost sounds like judging your print under what is the architectural standard for average light levels around the world could be of great importance. Is that figure 500 lux? From what I know a GTI viewing booth is,… 500 lux. Is 500 lux the baseline illumination level that the entire print industry judges prints under?

Am I making any sense here?
« Last Edit: April 23, 2021, 10:10:12 am by Harry Lime »
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #8 on: April 22, 2021, 10:41:51 pm »

As Andrew said, this is most easily done with eyeballs. But for nerd interest, the relationship between Lux and cd/m^2 is Pi. That is, a light source that is 500 Lux directly opposite a perfect, white paper produces the equivalent of a  500/Pi or 159 cd/m^2. But papers aren't perfectly white. A good matte paper might reflect 90% of the light hitting it. Which is why, if you have such a near perfect setup and a monitor at 159 cd/m^2, when you select "show paper white" in Photoshop's soft proof, you get a brightness decrease because the paper appears to be 143 cd/m^2.

The other major complication is getting the monitor's white point chromaticity to match the hard proof light. A good profiling package will allow you to match chromaticity.

Thanks for this, Doug

For all of those of us who went to art school, could you please write that up as a formula... :-)

thx
« Last Edit: April 22, 2021, 10:46:45 pm by Harry Lime »
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Doug Gray

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Re: Determining viewing light brightness for print
« Reply #9 on: April 23, 2021, 12:12:53 am »

For a "perfect" white matte paper, the formula for cd/m^2 (candelas per square meter) is:

cd/m^2 (sometimes called Nits) = Lux/3.14

But it's reduced a bit since no paper reflects 100% of the light that hits it.
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #10 on: April 23, 2021, 10:08:10 am »

Thanks Doug
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #11 on: April 23, 2021, 10:22:57 am »

A quick search of the internet yields this information.

Unsurprisingly there are guidelines and standards for illumination levels in buildings. And 300-500 lux is the recommended light level for exhibit spaces. It is also a common light level for general interiors.

My point is that it doesn't seem to make a lot of sense to review your print under a light level that is either too low or too high compared to the average encountered in the real world (500 lux, incident reading). Otherwise your print will not really appear as intend to the general public, in your average space.

If you judge your prints at 0200 lux (incident) they may appear too bright at 500 lux  (incident).
If you judge your prints at 1000 lux (incident) they may appear too dark at 500 lux (incident).

If you judge your prints at 0500 lux (incident) then they will probably appear as intended in most commercial spaces, including galleries.


Any thoughts?


https://www.archtoolbox.com/materials-systems/electrical/recommended-lighting-levels-in-buildings.html


Recommended Light Levels by Space

The table below provides recommended light levels from the IESNA Lighting Handbook and LPD levels from the IECC 2021 (using the Space-By-Space Method for calculations). Check your local jurisdiction for other or more stringent requirements. The US General Services Administration provides lighting levels and LPDs for US Government buildings, which can be used as a guide for other types of buildings. The LPD levels should continue to drop with subsequent codes and as LED lighting becomes more energy efficient.

The required light levels are indicated in a range because different tasks, even in the same space, require different amounts of light. In general, low contrast and detailed tasks require more light while high contrast and less detailed tasks require less light.

Please keep in mind that this chart is not comprehensive. The IESNA Lighting Handbook has pages and pages of various categories. If you have a very specific need, we recommend further research.

ROOM TYPE   LIGHT LEVEL (FOOT CANDLES)   LIGHT LEVEL (LUX)   IECC 2021 LIGHTING POWER DENSITY (WATTS PER SF)

Cafeteria - Eating   20-30 FC   200-300 lux   0.40
Classroom - General   30-50 FC   300-500 lux   0.71
Conference Room   30-50 FC   300-500 lux   0.97
Corridor - General   5-10 FC   50-100 lux   0.41
Corridor - Hospital   5-10 FC   50-100 lux   0.71
Dormitory - Living Quarters   20-30 FC   200-300 lux   0.50
Exhibit Space (Museum)   30-50 FC   300-500 lux   0.31
Gymnasium - Exercise / Workout   20-30 FC   200-300 lux   0.90
Gymnasium - Sports / Games   30-50 FC   300-500 lux   0.85
Kitchen / Food Prep   30-75 FC   300-750 lux   1.09
Laboratory (Classroom)   50-75 FC   500-750 lux   1.11
Laboratory (Professional)   75-120 FC   750-1200 lux   1.33
Library - Stacks   20-50 FC   200-500 lux   1.18
Library - Reading / Studying   30-50 FC   300-500 lux   0.96
Loading Dock   10-30 FC   100-300 lux   0.88
Lobby - Office/General   20-30 FC   200-300 lux   0.84
Locker Room   10-30 FC   100-300 lux   0.52
Lounge / Breakroom   10-30 FC   100-300 lux   0.59
Mechanical / Electrical Room   20-50 FC   200-500 lux   0.43
Office - Open   30-50 FC   300-500 lux   0.61
Office - Private / Closed   30-50 FC   300-500 lux   0.74
Parking - Interior   5-10 FC   50-100 lux   0.15
Restroom / Toilet   10-30 FC   100-300 lux   0.63
Retail Sales   20-50 FC   200-500 lux   1.05
Stairway   5-10 FC   50-100 lux   0.49
Storage Room - General   5-20 FC   50-200 lux   0.38
Workshop   30-75 FC   300-750 lux   1.26
« Last Edit: April 23, 2021, 10:51:11 am by Harry Lime »
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digitaldog

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Re: Determining viewing light brightness for print
« Reply #12 on: April 23, 2021, 10:50:55 am »

How many thousands of years have man produced art, how at over 100 years of photography this has not been a problem?

“There seems to be some perverse human characteristic that likes to make easy things difficult.” -Warren Buffett

Our eyes adapt to the illumination. Simple. The greatest Adams print will appear too dark if the only illumination is a 3watt nightlight bulb. Don't.
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JRSmit

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Re: Determining viewing light brightness for print
« Reply #13 on: April 23, 2021, 10:55:42 am »

Check internet on Arie Andries Kruithof.
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #14 on: April 23, 2021, 11:12:08 am »

How many thousands of years have man produced art, how at over 100 years of photography this has not been a problem?

Well, for thousands for years there also was no reliable and consistent interior lighting, so there wasn't much you could do about it. That's besides the point that most painters work by daylight, which naturally has a certain consistency to it.

Quote
“There seems to be some perverse human characteristic that likes to make easy things difficult.” -Warren Buffett

Our eyes adapt to the illumination. Simple. The greatest Adams print will appear too dark if the only illumination is a 3watt nightlight bulb. Don't.


True, but you are never going to see the print as Adams intended it, unless you saw it under a similar light level that he judged it under. Does that make his work any less enjoyable? Obviously not.

But Adams was a pretty smart guy and I would be very surprised if this had not crossed his mind at some point. He did exhibit widely and at some point must have noticed a discrepancy between how his prints looked back at his studio and a gallery or museum. He also had books printed in his lifetime and without a doubt he had to review and approve the reproduction of his work in these publications. As we all know he was not only a great artist, but also very technically skilled, so he would have not been ignorant of any discrepancies he was seeing and why they were occurring.

Years ago I saw a clip on TV about a very famous photographer setting up for an exhibit at a gallery and the man actually pulled out a light meter to check the brightness of the track lighting falling on the wall. It wasn't until now that it dawned on my why this person what did that.

It is certainly something I have noticed in my business. I work in post production for movies. One of the longest running gripes from directors is that the print viewed at the lab, which is calibrated to an industry standard, does not match your average theater, because the owner turned down the bulb brightness to make it last longer. This complaint has faded away, as we switched from film to digital projection, but it does go to show that some people are aware of inconsistencies in how their work is seen.


« Last Edit: April 23, 2021, 11:32:26 am by Harry Lime »
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digitaldog

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Re: Determining viewing light brightness for print
« Reply #15 on: April 23, 2021, 11:25:01 am »

Well, for thousands for years there also was no reliable and consistent interior lighting, so there wasn't much you could do about it.
Do about what? You're assuming there's a problem that AFAIK, doesn't exist.
IF you wish to match visually the display and print, doable and explained and now there's a photo below to show for the visually inclined. You are expected to use a rational kind of print illumination next to the display AND get all your ducks in order for a visual 'match'. From there, take that print and move it into any equally rational illumination (again, NOT a 3watt nightlight), it will appear fine as your eyes adapt to the illumination.
This has been the case, with just Photography long before displays existed.
Quote
True, but you are never going to see the print as Adams intended it, unless you saw it under a similar light level that he judged it under
Yes, you will.
Please dig up some text from Adam's discussing this issue for him too, if such an issue ever existed.
Quote
Years ago I saw a clip on TV about a very famous photographer setting up for an exhibit at a gallery and the man actually pulled out a light meter to check the brightness of the track lighting falling on the wall.
And that impressed you why? Is he going to take a photograph inside that gallery? A meter might indeed be useful. For anything else, it's just silly and goes back to the Buffett statement.
Quote
I work in post production for movies. One of the longest running gripes from directors is that the print viewed at the lab, which is calibrated to an industry standard, does not match your average theater, because the owner turned down the bulb brightness to make it last longer.
And if you view Adams prints under a 3watt bulb, or a black light etc, it will look awful. Don't do that. Pull out the meter? I suppose if you want to impress folks with equipment. Otherwise, this is all a very simple proposition that has been conducted for centuries.
As for how someone's work appears to others, you really want to get into a rabbit hole about human color perception, age, cataracts, surround etc? The hole is every deep.


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Frans Waterlander

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Re: Determining viewing light brightness for print
« Reply #16 on: April 23, 2021, 11:58:19 am »

Learn about color constancy!
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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #17 on: April 23, 2021, 12:01:23 pm »

Do about what? You're assuming there's a problem that AFAIK, doesn't exist.

Well, it is a problem for some. My father was a painter and the light he painted by was of concern to him. He was one of the least technical people I have ever known, an artist through and through and it even dawned on him that the way his paintings were seen was dependent on the lighting of the environment they were in. So, he painted near a very large window by daylight and was consistently frustrated by his inability to find an artificial light source that would emulate natural light. This mainly came from his desire to be able to paint all the way into the night. The old masters preferred northern day light. This is not a new concept or area of discussion.

Quote
IF you wish to match visually the display and print, doable and explained and now there's a photo below to show for the visually inclined. You are expected to use a rational kind of print illumination next to the display AND get all your ducks in order for a visual 'match'. From there, take that print and move it into any equally rational illumination (again, NOT a 3watt nightlight), it will appear fine as your eyes adapt to the illumination.
This has been the case, with just Photography long before displays existed. Yes, you will.

Yes, and it appears that the rational light level commonly found in the real world is around 500 lux (incident reading).


Quote
Please dig up some text from Adam's discussing this issue for him too, if such an issue ever existed.

I have read The Negative, The Print and many of his other writings.


Quote
And that impressed you why? Is he going to take a photograph inside that gallery? A meter might indeed be useful. For anything else, it's just silly and goes back to the Buffett statement. And if you view Adams prints under a 3watt bulb, or a black light etc, it will look awful. Don't do that. Pull out the meter? I suppose if you want to impress folks with equipment. Otherwise, this is all a very simple proposition that has been conducted for centuries.

Impressed? Hardly, and let's not be silly.

But it does go to show an awareness by the artist that they want their work seen as they intended it to be seen. It's hardly overcomplicating things to check that the light in the gallery is at a reasonable level.

There seems to be this assumption by the general public that artist are just a these untamed, mysterious creatures, that simply operate on emotion and technique never crosses their mind. Well, take it from someone who comes from a long line of artist, grew up in a family of artists and has spent an entire career working with artists. The best of them are absolute masters of technique. It's not all talent and many of them are concerned with the public seeing or hearing their work as they intended to be perceived.

Quote
As for how someone's work appears to others, you really want to get into a rabbit hole about human color perception, age, cataracts, surround etc? The hole is every deep.

Ball park figures. We're talking about a commonly found level of illumination found in the real world where your prints are going to be seen. No one is talking about running around like a lunatic with a light meter and obsessing about something with an almost infinite amount of variables that can not be controlled. But if your average exhibit space, office, store etc across the entire planet is illuminated at around 500 lux, then it is not such a crazy idea to assume that this may be a good baseline level of illumination to review your prints under.


For what it's worth, here is my work if anyone is curious to see it.

www.felidigiorgio.com

http://www.felidigiorgio.com/portfolio/0arswom08mqlpf7ftjiw1zqol49all

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Harry Lime

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Re: Determining viewing light brightness for print
« Reply #18 on: April 23, 2021, 12:08:03 pm »

Learn about color constancy!

My day job consists of digital image manipulation in a highly color calibrated environment. I have worked in post production for movies and television for the past 30 years, as a colorist and compositor for visual effects. You have probably put down your $10 for a ticket, so see some of the work I contributed to many times over. So, while I am not a color scientist, I am not completely ignorant about what we are talking about here.

But I am new to printing.
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digitaldog

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Re: Determining viewing light brightness for print
« Reply #19 on: April 23, 2021, 12:08:08 pm »

Learn about color constancy!
What have you learned?
This should be entertaining....  ;)
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