Meaning and use
Light resistance or weather resistance over a specific time period is associated with certain types of printed matter, such as magazine and book covers, posters and billboards, greeting cards and packaging. Since a print’s ability to withstand color changes is a function of the spectral power distribution of the light source to which it is exposed, it is important to evaluate light resistance under conditions suitable for the end use.

The accelerated procedures covered in these exposure methods provide a way to quickly assess light or weather resistance under laboratory conditions. The test results are very useful for specification acceptance and quality control between producers and users.

Xenon arc lamps with a proper filtration system exhibit spectral power distributions closer to daylight than carbon arcs. In turn, accelerated tests using xenon arc devices correlated better with exposure to natural light than accelerated tests using carbon arc devices.

To accommodate variations in light intensity between days, seasons, locations, or instruments, exposure duration is recommended to be expressed as radiation exposure in a particular bandpass, rather than time. In either case, the inclusion of appropriate controls helps minimize the impact of changes in test conditions.

Color change is not a linear function of exposure duration. The method of choice for determining light or weather resistance is to expose the print to multiple intervals and assess the time or radiation exposure required to obtain the specified color difference.

ASTM D3424-2011 “Assessment of Relative Sun Fastness and Weather Resistance of Printed Matter”

For a given printing ink, light resistance and weather resistance, or both, depend on the type of substrate, the film thickness of the print, and the printing area (solid vs. screen). It is therefore important that the properties of the test and control specimens correspond to what is expected under actual conditions of use.

Note 2 – Specifications D4302, D5067 and D5098 provide useful guidance for the light resistance of several types of artist pigments after 1260 MJ/m 2 Total window glass filtered solar radiation exposure (equivalent to about 2 or 3 months of exposure to window glass filtered solar radiation at a 45 degree inclination according to practice G24). However, due to the significant differences between the printing inks and the artist’s colors, especially in terms of the film thickness applied, it cannot be assumed that the light resistance classes of the printing ink films containing these pigments will be comparable to those indicated in the three specifications.

Radius
1.1 This standard describes procedures for determining the relative light and weather resistance of printed matter under the following conditions, which involve exposure to natural light or accelerated procedures in the laboratory:

1.1.1 Method 1 – Sunlight behind window glass

1.1.2 Method 2 – Outdoor Weathering,

1.1.3 Method 3 – Xenon arc device with window glass filter for simulating daylight behind window glass

1.1.4 Method 4 – Simulation of outdoor weathering with a water jet and daylight filter for xenon arc installations,

1.1.5 Method 7 – Fluorescent lighting device combined with window filtering daylight to simulate indoor fluorescent lighting.

1.1.6 Method 8 – Fluorescent lighting device operated with fluorescent cold white light to simulate indoor fluorescent lighting.

ASTM D3424-2011 “Assessment of Relative Sun Fastness and Weather Resistance of Printed Matter”

Note 1 – Previous versions of this standard included methods 5 and 6 based on closed carbon arc exposure. These methods are described in Appendix X1. The spectral irradiance of a closed carbon arc is a very poor simulation of solar radiation, the emission of a window glass filtering solar radiation, or a lamp used for indoor lighting. In addition, closed carbon arc devices are no longer readily available or commonly used.

1.2 These methods require a suitable print or other control (reference standard) to be run with the test sample. Color changes due to exposure conditions can be assessed by visual inspection or instrumental measurements.

1.3 These methods are applicable to prints on any flat substrate, including paper, board, foil, sheet metal and plastic film, and produced by any printing process, including letterpress printing, offset lithography, flexographic printing, gravure printing and screen printing.

1.4 Values expressed in SI units shall be regarded as standard values. No other units of measurement are included in this standard.

1.5 This standard is not intended to address all safety concerns, if any, associated with its use. It is the responsibility of users of this standard to establish appropriate safety and health practices and to determine the applicability of regulatory restrictions prior to use. See Section 8 for specific hazard descriptions.