The industry has made tremendous progress over the last five years in the performance of inkjet inks and media. There is now a host of wide-format printer systems capable of delivering photographic-image quality and color, and many specialty inks capable of achieving photographic lightfastness/fade resistance. The dilemma, however, has been that in order to provide great color, lightfastness had to be compromised – or vice versa.

Service providers have had to select inks for specific jobs based on the application, and a trade-off had to be made between initial image quality and durability over time. As a result, a different ink set may have to be loaded into the printer to run a subsequent job, costing valuable production time and labor – and wasting media and ink in the process.

An additional issue facing the industry has been agreement on a common way of assessing product performance. Kodak has long advocated a complete view of performance that includes ambient environmental effects such as temperature, relative humidity, and airborne pollutants in addition to light fade data. Although not a complete picture, we believe that in instances where light intensity is a dominant factor to overall performance a limited "light-only" view of product performance can be a useful reference point when making product comparisons.

In the commercial segment, few end users need or see value in display prints that last for tens or hundreds of years. In the midst of all the claims and confusion about fade resistance and lightfastness, most professional / commercial customers simply want to be sure that the materials they specify last as long as possible without unnecessarily forcing trade-offs in color density, cost or productivity. At Kodak Professional, we believe we have achieved the solution – a single, affordable solution – to this dilemma.

Kodak Professional Enhanced Imaging Lightfast-Plus inks and media provide a single solution that delivers both color equal to the best competitive inks and industry leading lightfastness. These new inks and media effectively eliminate need for constant ink changeovers and time-consuming printer calibration. The service provider does not have to compromise one desired trait for another, and now can achieve great image quality and color that lasts. Data from our research indicate that Kodak Professional EI Lightfast-Plus inks last two and a half times as long as the acknowledged leader for color fastness, yet retains the highest image quality.

Traditionally, printer manufacturers have provided hardware-based image-quality solutions that excelled in terms of color reproduction. Ink companies experienced in dyes have principally focused on providing lightfast solutions. But Kodak scientists, with their detailed understanding of color and image science, have combined more than 70 years of experience in innovative colorant technology with the knowledge gained over 100 years of making photographic media.

As a result, Kodak Professional’s newest inks employ patented dyes that provide great color and offer world-class performance in terms of lightfastness/fade resistance. Kodak has invented more than 30,000 dyes just for imaging over the years. We invent, develop, and manufacture these inkjet dyes the same way we do the dyes for our world-class film products – with both color and light stability in mind. Components are created and calibrated to provide a complete system/solution, not merely a collection of products, to provide the best available option for professional imaging labs and service bureaus.

As noted previously, until now, ink and paper combinations have been optimized either for color reproduction or lightfastness. Traditionally, manufacturers of inks with a high level of lightfastness have been required to trade off superior color gamut. Therefore, it’s important to understand the differences and interrelationship of these two attributes.

In achieving their results – Kodak Professional EI Lightfast-Plus inks deliver both lightfastness and color gamut without compromise – Kodak scientists made two critical breakthroughs in developing these new inks and media. They also have been awarded patents (U.S. Patents 5,997,622 and 6,001,161) in recognition of their efforts. When used in combination with the Kodak Professional 4700 series wide-format inkjet printers, these inks and media provide a unique, top-performing combination of lightfastness and color gamut.

Color gamut represents the breadth of colors and the number of discrete colors that a particular combination of printer, ink, media, and RIP (Raster Image Processor) can achieve. End users sometimes complain about "out of gamut" errors. These occur when a given color is simply not available from the selected "system." The RIP compensates by printing another color that the system can achieve, but this substitute may have lower density or the wrong hue.

Measuring color gamut is not simple, and expressing the results can be even more challenging. Color gamut can be expressed in several different ways (Appendix 1). It can be measured in terms of two-dimensional a*b* color space (as an area that represents the scope of gamut covered), or in three-dimensional CIE L*a*b* space. Kodak created a proprietary three-dimensional measure in this space,which uniquely factors in lightness as well as a* (green-magenta axis) and b* (yellow-blue axis).

We are confident this three-dimensional approach defines gamut more precisely, and we will refer to it in this presentation. But because of the confidential nature of this proprietary methodology, we will express color gamut in terms of the two-dimensional a*b* color space that is more familiar to most readers. Although these two-dimensional plots can be misleading at times (in that they ignore lightness), they offer a more simple expression of color gamut and reflect how most people in the industry view and interpret it.

Examination of the color gamut comparison graph in Figure 1 clearly shows that Kodak Professional EI Lightfast-Plus inks offer a larger gamut over the leading competitor. In addition, the plots show these inks to have enhanced reds, purples, and blues as indicated by the additional gamut areas in the lower right-hand portion of the plots.

Figure 1

Figure 2 shows a comparison of the calculation of the total color gamut three-dimensional volumes by the proprietary method mentioned above. This method provides a single quantitative measure of color gamut, and shows that the Kodak Professional EI Lightfast-Plus inks have a much larger color gamut than the leading competitor.

Figure 2

Although the results in Figure 2 appear to be more straightforward, they should be looked at in conjunction with the two-dimensional graph, which better illustrates specific areas of strength or weakness. A more complete understanding of color gamut requires that these measures be used together to characterize its overall scope and nuances.

For an inkjet print, the assessment of "print life" usually involves a highly subjective process. The life of a print can depend on any number of factors:

intended application

color density of the original image

determining whether the print is exposed to direct sunlight or daylight

duration of that exposure

use of a filtered or unfiltered light source

measuring the loss of print density or fading the customer expects and will accept

In addition, the effects of humidity, heat, air pollution or other environmental factors can also degrade the realized life of customer prints. Given this variety of conditions and applications and the subjective nature of individual assessments, it is extremely difficult for manufacturers, service providers, and end users to uniformly estimate and assess print life. Yet this is precisely what service providers must know to make sound business decisions.

Kodak research scientists and the Kodak Professional product team have worked to identify a process for evaluating and measuring inkjet print performance in the higher-intensity, large-format commercial display market. While not an absolute measure of print life, this approach provides a controlled way to document the relative performance of competing technologies. ¹ Rather than varying numerous variables in terms of duration of exposure, light energy values, and direct/indirect exposure, we used a comparative approach that applies a standard ANSI methodology (Appendix 2) and enables a controlled test of individual combinations of inks and media.

While there are many contrived answers to the question of print life, we advocate employing a fact-based, objective method to produce results so that a fair comparison can be made. Given the controlled nature of the tests, results can be compared directly across different manufacturers’ offerings. This approach offers a useful tool to evaluate and select appropriate technologies without the potential for confusion in terms of variations in exposure conditions (direct/indirect), light energy values or duration to arrive at a desired result. A direct comparison of performance provides a legitimate way for fabricators to make informed choices both today and over time, and to offer the best value to the end users of these products.

Things start to get confusing when projections are made regarding print life. It is critical to note that there is not yet an industry standard for lightfastness/fade resistance testing. So many of the claims that end users encounter in the trade media have been calculated using different failure criteria, varying test lighting conditions, and individual assumptions about lighting conditions for a specific application.

For example, most experts assume the common commercial display conditions in a mall, store or other retail location to be 450 lux of light exposure, for 12 hours a day, under fluorescent light. ² Rather than waiting for the results of lightfastness testing in real-time, manufacturers have employed accelerated testing to speed their learning. This approach is based on the assumption that fading is a function of exposure (E), and that exposure is the product of intensity (I) and duration (t).

By increasing the intensity of the light (I), testers are able to deliver higher exposure levels in the same amount of time, thereby accelerating the impact of exposure. The high-intensity bulbs typically used in most accelerated tests, and the type used in our accelerated testing, produce 50,000 lux. To further accelerate results, images were exposed to this level of intensity for 24 hours a day. If we make the assumption that the image fades reciprocally (see below), one day in a high-intensity test chamber under these assumed display conditions is equal to 222 days in real life.

Taking the number of days in the high-intensity test chamber until failure, and converting them into years as calculated above, we find that the print made with Kodak Professional EI Lightfast-Plus inks has an estimated print life of at least 33 years. In comparison, the leading competitor lasts only 13 years. On the basis of this direct comparison, Kodak Professional EI Lightfast-Plus inks and media outperformed the acknowledged industry leader for lightfastness – lasting 2.5 times as long.

But what if the light intensity at the retail location is different? Suppose the print is in a location where the light exposure is less, or the store simply has lower intensity bulbs or covers on the lights? Some manufacturers have assumed indoor display conditions with a light intensity as low as 200 lux in their calculations of print life (called "Low-Intensity Commercial Display"). What happens to the print life under these conditions? Our calculation from above needs to change to account for the lower daily light exposure.

With this modification, we now find that inkjet prints using Kodak Professional EI Lightfast-Plus inks have an estimated life of 75 years, while the leading lightfast competitor lasts 29 years. Figure 3 below summarizes these results graphically.

Figure 3

One final consideration is the use of filtered vs unfiltered light. The test methodology we employed used unfiltered light, exposing the inks and media to the maximum amount of light from the high-intensity source. Many other predictors of print life test their prints using Plexiglas™-filtered light or under glass, which can filter out some of the light, reducing exposure and extending the predicted life of their prints by 2-3x. ³ Using such an approach, it may be possible to derive durability claims of 150 to more than 200 years for the Kodak Professional EI Lightfast-Plus inks and media tested.

So how many years do prints last? It all depends. As we’ve noted, the variables it depends upon are highly subjective and extremely sensitive. Given the leverage provided by the high-intensity test light, which may be greater than 100x the actual environmental conditions, even modest changes in individual variables or assumptions can greatly skew projected lifetime results. This latitude can lead to performance claims that are at best confusing and at worst misleading to end users.

An additional issue is the underlying assumption that the relationship of light exposure and fading is reciprocal and, therefore, the results of accelerated tests are easily projected to actual use conditions. If the print reacts reciprocally, that means the amount of fade the print undergoes is related only to the total amount of light that reaches its surface, and not to the intensity of the light source or the duration of exposure. Deviation from this behavior is called reciprocity failure in the literature. ⁴ If reciprocity holds, then these accelerated tests will accurately predict the print life. If not, then these tests can produce erroneous results when converting the amount of fading to actual years.

In addition, in the lower-intensity extrapolations, there has been no accounting for the effects of thermal degradation, which become increasingly important, and could become more limiting than lightfastness as ambient illumination intensity is reduced.

So claiming a print life in years is difficult and potentially misleading. Estimated life statements are "all over the board." Manufacturers seem able to justify these differences by pointing to "concrete" test results without satisfactorily acknowledging the sensitivity of these projections to the formulae they are using to calculate their estimates. (Appendix 3)

An alternative approach to judging print life that avoids the issues of converting accelerated data into print-life estimates in years is to simply compare prints exposed to the same conditions. Such a controlled test provides a direct, objective comparison of fade resistance. Because these results are not factored in any way and a standard measure of density is used to assess "failure," there is little or no room for subjectivity in the results.

Kodak Professional supports testing inkjet prints using test conditions that most closely match the way customers actually display prints, and advocates using failure criteria that are common in the industry. A leading independent testing service ⁵ has evaluated Kodak Professional’s combination of inks and glossy inkjet papers, following the guidelines set forth in ANSI/NAPM IT9.9, 1996. We believe this is a method that will ultimately prevail, as it provides a legitimate basis for industry-wide indoor light fade testing in the higher intensity, large-format commercial market.

Figure 4

Using the same methodology, results of our "relative comparison" testing include those of the leading competitor, long considered the benchmark for lightfastness in inkjet prints. The failure criteria used standard measures explained in Appendix 2. They were applied consistently to both samples and include a combination of primary color and secondary color fade. Total exposure was measured until a predetermined color-density end point was achieved. The data supporting Figure 4 show the relative results of these tests: Kodak Professional EI Lightfast-Plus inkjet prints last 2.5 times longer than the leading competitor, the previous de facto standard for inkjet durability – and delivered best-in-class color gamut as well.

We have reviewed various methods for measuring color gamut and lightfastness, and have pointed out those methods we feel best provide customers with a legitimate way to compare product performance.

This paper has demonstrated some of the ways in which it is possible to derive print-life claims in excess of 100 years, essentially by adjusting test conditions and environmental assumptions. Many of the values for assumptions used to support claims in the trade press fall outside of expected values for typical applications. Such examples include the use of filtered light, light under glass or "low intensity" light sources of 200 lux. These assumptions could misrepresent the actual performance of the product to end users.

Based on side-by-side controlled testing and direct comparisons, Kodak Professional demonstrates first-in-class performance in terms of lightfastness, and delivers color gamut that is at least equivalent to the most colorful inks in the industry (inkjet prints produced on a Kodak Professional 4700 series inkjet printer using EI Lightfast-Plus inks).

We have discussed in creating these products, how Kodak Professional has leveraged Kodak’s proprietary knowledge and experience in image science to the benefit of our customers.

We have demonstrated that Kodak Professional can save imaging labs and service providers time and money – and most importantly deliver best-in-class inkjet prints that will far exceed end user requirements for image quality and durability.

Finally, we have established that there is no longer a need to trade off color gamut for lightfastness. Imaging labs, service providers, and end users no longer have to compromise if they use Kodak Professional Enhanced Imaging Lightfast inks and media in a Kodak Professional 4700 Series Inkjet Printer.

1 Kodak scientists continue to work on better methods of defining print life encompassing all of these variables, and we intend to work with industry bodies to standardize those definitions. 2 Consumer storage and display conditions could be dramatically different. 3 Bugner and Suminski, Proc. IS&Ts NIP 16, 2000; and Carmody, Evans, and Robinson, Proc. IS&Ts NIP 16, 2000. 4 James, The Theory of the Photographic Process, 4th Ed., p133. 5 Data from independent tests performed at the Image Permanence Institute at Rochester Institute of Technology.