The Right White Light

Brian Lawler

2

We live with metamerism. It skulks around and tricks us into seeing things that aren’t as they appear. Or maybe it tries to get us to see things that don’t appear as they are. Whatever it does, I looked it up in Webster’s dictionary and here is what that esteemed reference book says:
“Metamerism n. (1877) the condition of having, or the stage of evolutionary development characterized by a body made up of metameres”
So, following that link, I found metameres (just one listing up):
“Metamere n. (1877) any of a linear series of primitively similar segments into which the body of a higher invertebrate or vertebrate is divisible”
So, I suppose that a metameric vertebrate is one that can be divided up into subparts: head, torso, legs and arms. I can imagine being metamerized by the sudden failure of an airplane, for example, with the flight attendant saying, “In the unlikely event of metamerism, your seat cushion can be used as a flotation* device.”
This, of course, has nothing to do with the metamerism to which I refer, a completely different metamerism which is described (by me) as the effect of different lighting conditions causing a varying appearance of a color on a printed sheet. I don’t know why this definition is not in my dictionary. And, since I’m being dictionaric…**
To wit: Under one lighting situation it looks great; under another lighting situation it looks awful.
Consider the (Light) Source
This really happens, and the results can be serious, often leading to disgruntlement*** on the part of our customers. What I mean here is that when customers don’t like the way it looks in their viewing conditions, the job has to be revised until it meets their standards. Metamerism has commercial consequences that are significant and troublesome.
This is why we have viewing booths and lighting standards – and it’s a good thing! Without a standard for viewing and receiving customer approval of a proof or press sheet under standard lighting conditions, we’re beyond hope.
When one considers the lighting considerations of the world, and of customer offices and homes, it’s no wonder that lighting standards exist.
I found eight different types of fluorescent lamps at Sylvania’s web site (I suspect that there are even more in its commercial listings). Sylvania lists: Cool White Fluorescent, Cool White Energy Saver Fluorescent, Economy Cool White Fluorescent, DESIGNER® Warm White Fluorescent, Warm White DELUXE Fluorescent, Warm White Fluorescent, and Warm White Energy Saver tubes.
Hmmmm. Which should I get? I fluoresce with frustration!
The same printed piece, when viewed under these various light sources, will look quite different. We call this metamerism. And, a printed product that suffers from too much metamerism is one that will cause you a great deal of grief in the real world of printing and publishing.
Unless you have a viewing booth with industry standard lighting.
ISO to the Rescue!
The International Standards Organization (ISO) has prepared a new lighting standard for the printing and publishing (technically photographic) industries. Called ISO 3664, the standard brings the entire world into compliance with one (yes, only one!) reflective viewing standard (5,000° K) and a number of other recommendations for viewing images on computer monitors and original images in a lighting booth or transparency viewer. Once printers worldwide adopt the standard, a proof made in Lisboa, Portugal and approved in proper viewing conditions in Rochester, Minnesota can be printed in Mumbai, India with success. Everyone will be using the same viewing conditions and should see the same thing.
The new ISO standard, approved March 21, 2000, will become The Law of the graphic arts industry.
As long as customers and printers use the same lighting standard, the issue of metamerism will be minimized in the approval of proofs and the production of printing. This does not mean that the problem of metamerism will disappear, only that the viewing standard for viewing images will have been equalized worldwide.
Metameric Meltdown
My recent memorable experience with metamerism occurred in Dallas, Texas in March. I was in the final stages of preparing for an all-day seminar on color management. We had printed corrected samples of test photos on two printing machines — one was the Tektronix Phaser 780 (my favorite pre-prepress printer) the other was a Hewlett-Packard 2500 DesignJet wide-format ink-jet printer (reputed to be the best in its class for color quality).
The objective was to demonstrate to an audience that color management actually works. It seemed like a simple challenge, and I had told my sponsors that if we couldn’t make it work in this seminar, we were all in the wrong business. After hours of preparation and profile-building, we made proofs to demonstrate our success.
Or lack thereof.
The proofs looked significantly different. I was unnerved and exhausted. Not sure of the route to take, I just sat down and closed my eyes for a few minutes. When I reopened them I looked at the ceiling — voila! The lighting in this particular hotel ballroom was a combination of incandescent (with dimmers) and fluorescent tubes. We were being foiled by metamerism!
One of our sponsors was GTI, maker of a viewing booth specifically for the electronic publishing industry. They had sent a unit called SoftView to the seminar. We unpacked the GTI unit, put our print samples in, and turned the lights on. Lo and behold, the two images matched almost perfectly. I was thrilled! I was not amazed, but I was relieved that the two were measurably, scientifically and certifiably “very similar.”
Our objective was met, and we (finally) got some rest before our all-day event the following morning.
Laying Down the Law
I decided not to change anything in our demonstration. Metamerism is a fact of commercial life, and to be able to demonstrate a metameric failure in the circumstances of the seminar was a Big Plus. Not only would it be possible to show the effects of metamerism, it would be possible to demonstrate how to solve the problem with a viewing booth of proper design.
My seminar was actually improved by the bad lighting in the room – and the availability of the GTI light booth. At the end of the day I held up the samples and proclaimed them to be matches — yet everyone could see they were not. Then I invited those in attendance to look at the same proofs in the GTI booth, and they were similarly impressed by the effect of metamerism and the quality of the view when viewed on industry-standard lighting.
A member of my audience asked, “Why, if we always view printed products in room light or office light, do we need a viewing booth to approve the proof?”
Obviously we don’t have 5,000° K lighting in our offices, stadiums and homes, but we cannot predict exactly where anything will be viewed, so we have a standard for viewing and approval of all printed products. That standard allows for the approval of a printed product despite the fact that it will usually be used in different lighting circumstances.
There is no rule that says you must print for 5,000° Kelvin. You are welcome to create art that is lighter or warmer or anything. But, you must approve the color under the standard viewing conditions. That’s The Law
Metameric Failure
One of the clever things I have acquired in my career is a lighting device that demonstrates metamerism (or lack thereof). I use it in my seminars to demonstrate how lighting changes the appearance of objects and printed samples.
Made by Tailored Lighting, Inc., it is a device with a variable light source. By moving a slider, you can change the color temperature of the light from indoor to daylight and everything in between. Used in carpet and paint stores, it is an amazing tool for demonstrating metamerism. My only wish is that it would have a Kelvin meter to indicate the color temperature while you are experimenting.
The Graphic Arts Technical Foundation has a commercial product to show metamerism. Called the GATF/RHTEM Light Indicator for Correct Viewing, you view it in 5,000° K lighting conditions and it appears to be a single bar of purplish color. When you view the same strip under incandescent lighting, the bar becomes several bars of two different colors, exhibiting metameric failure due to lighting. These little strips are useful for demonstrating that the viewing booth lighting is right (or wrong). And, it’s a great educational tool.
So, next time you are faced with the classic problem of colors not matching in the office (but they matched in the printing plant!), you can ascribe it to metameric failure. At least you know the definition of the word, and you know that you can’t do much about it except accept it.
(And I’m off to the dictionary for the definitions of accept and except!).