Digital Prints

■ Waterfastness (for waterfastness and outdoor durability: the drip test, the pour test, the
standing water evaporation test, the standing water plus gentle wipe test, and the water
smear test) (See Figure 5.5.)
■ Humidity-fastness
■ Fingerprint Test (for handling damage)
■ Chemical and Biological Stability (to test resistance to attack by chemicals and biological
agents)
Choosing the Light
Chapter 5 ■ Determining Print Permanence 159
One big debate around lightfastness testing is this: What type of light source should be used in the testing? Here’s a quick rundown of the three
main choices.
Fluorescent has been the favorite of the major testing organizations and manufacturers for years, but it has obvious flaws, including not accurately
simulating most indoor lighting conditions due to its unusual spectral power distribution (see accompanying illustration). Fluorescent is
useful for prints destined for display exclusively in stores or offices, but many doubt its appropriateness otherwise.
Natural sunlight is the original light source, and because it covers the spectral range with ultraviolet, visible, and infrared radiation, many
use it for testing. Some, however, question its validity since added variables (like heat) are introduced. Also, natural sunlight may vary from
season to season.
Xenon arc lamp testing is done with a special device (see illustration on page 161 and Figure 5.9 in this chapter) that provides the best available
approximation of full-spectrum sunlight. Using filters to simulate either sunlight through a window or direct outdoor exposure to sunlight, the
other advantages of xenon arc testing are that the variables can be controlled, and the results are fast. The main disadvantage is the cost of the
expensive machines.
What’s the answer? ASTM’s approach is to specify in their D4303 standard that at least two of four different light-source conditions be tested and
then compared: filtered xenon to simulate daylight, outdoor sunlight in Arizona, outdoor sunlight in Florida, and special fluorescent lamps (these
may be removed in the next version of the standard). (See more about ASTM’s testing standards next).
The spectral power distributions
(SPDs) of three common light sources:
sunlight through glass (gray), xenon arc
(red), and cool white fluorescent (blue).
Note how closely the sunlight and
xenon match yet how different the
fluorescent is.
Courtesy of Q-Panel Lab Products