Light fastness

 

 

Principle
A test specimen taken from the laminate under test is exposed to daylight simulated by the filtered light of one or more xenon arc lamp(s). The effect on the color of the specimen, at a specified radiant exposure, is assessed by the contrast between the exposed and unexposed portions of the test specimen. The radiant exposure is determined both instrumentally, and by assessing the effect on
blue wool references which are exposed simultaneously.
Daylight spectral distribution is specified as decorative laminates may, in certain applications, be exposed to direct daylight through open windows.

Apparatus
1. A test device, as specified in EN ISO 4892-1 and EN ISO 4892-2, equipped with:
– one or more xenon arc lamp(s) filtered to provide a spectral energy distribution which closely approximates to that of solar radiance.
– stainless steel specimen holders, in the form of an open frame, which provide the test specimens with a solid backing;
– a black-standard thermometer according to EN ISO 4892-1;
– a photoelectronic sensor according to EN ISO 9370 to measure the irradiance and the radiant exposure at the specimen surface in the wavelength range 300 nm to 400 nm, or 340 nm.
2. Conditioning chamber, in accordance with EN ISO 291, with a standard atmosphere of (23 ± 2) °C and relative humidity (50 ± 5) %.
3. Viewing enclosure, having a matt interior colour corresponding approximately to Munsell N5.
It shall be equipped with an artificial light source, located at the top, simulating average north sky daylight (e.g. tungsten-halogen incandescent lamps) and generating a colour temperature of (6500 ± 200) K and at least 800 lux on the surface of the specimen. The viewing enclosure shall be placed in a position where the surrounding lighting conditions will not affect the visual assessment of
the specimen.

Test specimen
One test specimen shall be prepared in accordance with EN ISO 4892-1.It shall be representative of the laminate to be tested, cut to the size required for the specimen holder used, and appropriate for the method of assessment after exposure.

Procedure
The test specimen and a set of blue wool references 5, 6 and 7 (according to ISO 105-B02) shall be exposed simultaneously. Blue wool references 5 and 7 are included to provide confirmation that wool reference 6 has degraded to the specified degree of contrast.
Using opaque stainless steel covers, shield approximately one half of both the test specimen and the set of blue wool references.
Carry out the test in accordance with EN ISO 4892-2 with the following operating conditions:
– irradiance at the test specimen surface in the wavelength range 300 to 400 nm :(60 ± 3) W/m2; or at wavelength 340 nm :(0,5 ± 0,03) W/m2
– black-standard temperature :(65 ± 3) °C
– relative humidity:(50 ± 5) %
Discontinue the exposure when the contrast between the exposed and unexposed portions of the blue wool reference 6 is equal to grade 4 on the grey scale, as defined in ISO 105-A02 (see note 1).
Measure and record the radiant exposure (300 to 400 nm, or 340 nm).
Remove the test specimen from the apparatus, take off the cover, and leave the specimen for (24 ± 2) h in dark conditions in the conditioning chamber to prevent extraneous darkening and/or phototropism.

Assessment and expression of results
Place the test specimen in the viewing enclosure.
Examine the surface of the test specimen with the naked eye, corrected if necessary, at a distance of approximately 50 cm for any change in colour, assessing the contrast between the exposed and unexposed portions of the test specimen in terms of a grade on the grey scale according to ISO 105-A02.
The light fastness of the test specimen is expressed in terms of the contrast being greater than, equal to or less than grade 4 of the grey scale.