Matching Critical Solar UV
Atlas Right Light® filters for Ci and Xenotest® accelerated weathering instruments provide the closest match to natural solar radiation in the critical UV wavelength region.
UV radiation from the sun is the most critical stress factor for photodegradation of polymers. In the so-called “cut-on” wavelength region, a few nanometers may make a significant difference in ageing of sensitive materials.
Therefore, matching the worst-case solar reference spectrum in the UV as good as technically possible is critical for realistic, correlating, and reproducible laboratory weathering testing. Since the mid 1950’s, xenon-arc lamps combined with optical daylight filters have been and still are the most reliable light source for this purpose.
The Right Light Story
Many optical filter systems produce a spectral irradiance distribution similar to natural sunlight. However, the existing standards have been allowing relatively wide tolerances, also in the critical UV region. In several cases, this variability in testing spectra reduced both reproducibility and correlation.
To better reproduce ageing behavior of paints in South Florida, a new standard, ASTM D7869 for transportation coatings, was published in 2014. One of the key improvements was the introduction of a new filter system: Right Light®, developed by Atlas in cooperation with automotive OEM’s
Comparison of Right Light (Daylight Type I), Daylight Type II, and solar radiation in the UV
Standards
The superior “Right Light” spectrum in ASTM D7869 was quickly adopted by the PV industry: In 2017, IEC TS 62788-7-2 on weathering tests of polymeric PV materials specified Right Light®.
Today, an increasing number of international standards such as ASTM D3794-16 for coil coatings, ISO 18768-1 and 2 for organic coatings on aluminum, as well as OEM specifications for automotive and consumer electronic applications refer to the Right Light® filter or comparable daylight filter types.
For improved reproducibility of laboratory weathering tests, ASTM and ISO have split their daylight spectral requirement for xenon light sources into two more narrowly defined types:
• Daylight Type I: UV cut-on very similar to natural solar radiation. Right Light® falls into this category.
• Daylight Type II: slightly lower UV cut-on compared to natural solar radiation. Examples are the legacy Boro S/Boro S or XENOCHROME 300 filters.
Meanwhile, Daylight Type I and Type II have been included into the basic weathering standards ISO 4892-2 for plastics, ISO 16747-2 for coatings, and ASTM G155 for various materials.
Right Light for Ci Weather-Ometers® and Xenotest®
Right Light® filters are available for Xenotest® 440 and 220+. Ci Weather-Ometers® can be equipped with two variants:
• Right Light® / Quartz: for “normal” weathering tests
• Right Light® / CIRA Coated Quartz: for lower test specimen temperatures
More Information
A brand new technical guide on Right Light® provides further details on this filter system. For more information about ASTM D7869 and other relevant standards, Atlas offers a technical guide as well as a recorded online seminar on automotive exterior and interior testing.
Furthermore, the Atlas Knowledge Center provides numerous video tutorials,technical documents and a training schedule.