Explaining the Differences Between Type I and Type II Daylight Filters

Atlas produced a daylight filter system for xenon-arc weathering a few years ago, which was a closer simulation to natural solar radiation compared to any of the filter systems on the market.

Explaining the Differences Between Type I and Type II Daylight Filters

Image Credit: Atlas Material Testing Technology LLC

The technology is called the Right Light™ filter. This filter system was initially deployed in the standardization of the ASTM D7869 method for transportation coatings. For photochemical deterioration, the solar UV cut-on is an important factor.

While the Right Light™ filters significantly differ from the conventionally used Boro-S/Boro-S type filter systems, each of these daylight filter configurations meets the same guidance of popular standards, for example, ISO 16474-2, ISO 4892-2 and ASTM G155.

The Problem

The types of daylight filters used are not differentiated in the standards ISO 16474-2, ISO 4892-2 and ASTM G155.

This frequently resulted in conflicting test results for materials that are sensitive to short wavelength UV radiation beneath the solar UV cut-on when various daylight filters were employed for the same kind of measurement.

To clarify, Atlas recognized the possible inconsistencies and influenced the inclusion of novel types of daylight filters in the international standards. The first committee was ISO/TC 61/SC 6 “Plastics - Ageing, chemical and environmental resistance” which adopted this and recently published the following document:

ISO 4892-2:2013/Amd 1:2021(en) Plastics - Methods of exposure to laboratory light sources - Part 2: Xenon-arc lamps - AMENDMENT 1: Classification of daylight filters.

The Solution

The category of Type I daylight filters is now used to include filters with a close similarity to natural solar radiation, such as filters that meet the standards of ASTM D7869. The Boro-S/Boro-S filters conventionally featured in Ci instruments are now categorized as Type II daylight filters.

Explaining the Differences Between Type I and Type II Daylight Filters

Image Credit: Atlas Material Testing Technology LLC

In a collaborative approach, the committee's ISO TC 35/SC 9 (Test methods for varnishes and paints, ISO 16474-2) and ASTM G03 (General weathering, ASTM G155) will soon align, reducing the concern about various specifications for daylight filters in different committees.

The goal of these revisions was not to argue that type I filters are superior to type II filters, although it is clear that type I is more practical.

The aim was to make users understand that the results may be inconsistent if a range of daylight filter types are utilized and to highlight that it is best to use the same type of filter for comparisons between different tests.

How Does this affect Weathering Testing?

The same filters can be used as before, in line with ASTM G155, ISO 16474-2, or ISO 4892-2.

The only recommendation is to explain which type of daylight filter has been employed in the test report. Understanding the daylight filter type utilized enhances the repeatability and comparability of weathering testing.

Explaining the Differences Between Type I and Type II Daylight Filters

Image Credit: Atlas Material Testing Technology LLC

For more information on the Atlas Right Light™ filter, contact ATLAS today.

Acknowledgments

Produced from materials originally authored by Dr. Florian Feil from Atlas Materials Testing.

Click here to download the Technical Note

This information has been sourced, reviewed and adapted from materials provided by Atlas Material Testing Technology LLC.

For more information on this source, please visit Atlas Material Testing Technology LLC.

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