Xenon arc weathering testing is widely used to evaluate how materials respond to simulated sunlight, heat, humidity, and moisture. Two of the most commonly referenced standards in this field are ASTM G155 and ISO 4892-2.

Although both standards use xenon arc light sources to simulate the effects of natural sunlight, they are not identical. Understanding their differences is important when selecting a Xenon Arc Weathering Tester, establishing test conditions, and comparing results from different laboratories.

I. What Is ASTM G155?

ASTM G155 – Standard Practice for Operating Xenon Arc Lamp Apparatus for Exposure of Materials establishes the basic principles and operating procedures for xenon arc exposure equipment. The current ASTM edition is ASTM G155-25.

The standard describes the use of optically filtered xenon arc lamps under controlled environmental conditions. Depending on the application, exposure can include light, heat, humidity, and water.

An important point is that ASTM G155 is primarily an apparatus and exposure practice. By itself, it does not prescribe one universal exposure condition or provide a specific pass/fail result. The appropriate exposure conditions and methods for evaluating material changes are generally defined by the relevant material-specific standard or specification.

II. What Is ISO 4892-2?

ISO 4892-2:2013 – Plastics — Methods of exposure to laboratory light sources — Part 2: Xenon-arc lamps specifies methods for exposing specimens to xenon-arc light in the presence of moisture.

The purpose is to reproduce weathering effects associated with actual end-use exposure to daylight or daylight filtered through window glass. Controlled conditions can include temperature, humidity, wetting, irradiance, and different xenon-arc lamp filter combinations. ISO states that the 2013 edition was reviewed and confirmed in 2023 and remains current, with an amendment concerning the classification of daylight filters published in 2021.

Unlike the broader material exposure concept of ASTM G155, ISO 4892-2 is specifically located within the plastics standards series.

III. ASTM G155 and ISO 4892-2: What Do They Have in Common?

The two standards have a strong technical relationship. Both use filtered xenon arc radiation to simulate the effects of natural sunlight and both address controlled environmental exposure involving factors such as temperature and moisture.

ASTM itself states that ASTM G155 is technically similar to ISO 4892-2, as well as several other international xenon-arc exposure standards.

Both standards emphasize that the test result depends not simply on the xenon lamp itself, but on controlled exposure conditions. Important factors include the optical filter system, irradiance, temperature, humidity, wetting or water exposure, and the condition of the equipment.

IV. The Main Difference: Scope and Application

The biggest difference is scope.

ASTM G155 is a general practice for operating xenon arc lamp apparatus for exposure of materials. It provides principles and procedures for obtaining, measuring, and controlling exposure conditions. It is intended to be used together with material-specific test methods or specifications.

ISO 4892-2 is specifically part of the ISO series for plastics and provides methods for exposing plastic specimens to xenon-arc light under controlled conditions.

Therefore, choosing between the two should not simply be based on which standard is considered “better.” The correct standard depends on the material being tested, the applicable product specification, and the required exposure conditions.

V. Can ASTM G155 and ISO 4892-2 Results Be Compared Directly?

Not necessarily.

Even though the two standards address closely related xenon-arc exposure technology, a test duration in one standard should not automatically be treated as equivalent to the same duration in the other.

Exposure conditions must be considered as a complete set. Differences in irradiance, filter configuration, temperature, humidity, water spray, and exposure cycle can affect material degradation.

ASTM G155 also emphasizes the importance of reporting the specific operating conditions because variations within permitted conditions can lead to variations in results.

For this reason, when comparing test results from different laboratories, it is important to confirm not only the standard number but also the actual exposure parameters.

VI. Which Standard Should You Use?

The answer depends primarily on the material and the applicable product standard.

For plastics and polymer materials, ISO 4892-2 is a commonly referenced international method, while ASTM G155 is widely used as the xenon arc exposure practice in ASTM-based testing programs.

For products covered by a specific ASTM or ISO material standard, the material-specific standard should normally determine the required exposure conditions. For example, ASTM has separate xenon-arc practices for particular materials and applications, which operate in conjunction with ASTM G155.

For geotextiles and geosynthetic materials, the applicable product-specific standard should be checked carefully rather than selecting ASTM G155 or ISO 4892-2 solely because both use xenon arc lamps.

VII. Conclusion

ASTM G155 and ISO 4892-2 are closely related xenon arc weathering standards, but they should not be regarded as completely interchangeable.

ASTM G155 is a broader practice covering the operation and control of xenon arc exposure equipment for materials, while ISO 4892-2 provides xenon-arc exposure methods specifically within the plastics testing framework. Both standards emphasize controlled radiation and environmental exposure, but the actual test conditions should always be selected according to the material and applicable product requirements.

For laboratories and manufacturers, understanding the differences between these standards can help ensure that the Xenon Arc Weathering Tester is configured correctly and that test results are meaningful, reproducible, and suitable for the intended application.