Meaning and use
4.1 Because solar radiation, air temperature, relative humidity, and the amount and variety of atmospheric pollutants are constantly changing, time-elapsed exposure results can sometimes vary. Variation in results is usually reduced by timing exposure in the following ways:

4.1.1 One or more environmental parameters, such as solar radiation exposure

4.1.2 Changes in predefined properties of aged reference specimens with known properties.

4.2 Changes in temperature, humidity and atmospheric pollutants can have a significant impact on degradation caused by solar radiation. In addition, exposure at different times of the year can lead to huge differences in the rate of degradation. Different materials typically have different sensitivities to heat, moisture, and atmospheric pollutants, which could explain the difference in ranking of samples exposed to equivalent solar radiation exposure when other environmental conditions change.

4.3 As the installation method has an impact on the temperature and other parameters of the specimen during exposure, the parties to the contract shall agree upon the installation method of the specimen for the particular exposure test being considered.

ASTM G24-2021 Standard Test Method for Exposure Tests in Sunlight Through Glass

4.4 There are differences in the transmittance of various single-strength window glass in the region of 300 to 350nm. For example, at 320 nm, the transmission of seven different batches of single-strength window glass ranged from 8.4% to 26.8%. At 380 nm, the percentage transmittance ranges from 84.9% to 88.1%.

4.5 Differences in UV transmittance between different batches of glass usually persist even after sun exposure. The biggest difference in UV transmittance of window glass is in the spectral range of 300 to 320 nm.

4.6 This practice is suitable for testing the relative properties of the material at the same time after comparing the same batch of glass. Because of the differences between large amounts of glass and exposure performed at different times of the year, it is not recommended to compare the amount of degradation of materials exposed for the same duration or radiation exposure at different times, or individual fixtures using different batches of glass.

4.7 Exposure to at least one control material with known properties is recommended for each test. The composition and structure of the control material shall be similar to that of the sample, and its failure mode shall be selected to be the same as that of the material under test. It is recommended to use two control materials, one with relatively good durability and one with relatively poor durability. When control materials are used as part of a test, they should be used to compare the properties of the test material with respect to the control.

4.8 Because some materials may degasses during exposure and may contaminate other specimens, it is recommended that only similar materials be exposed to the same glass cabinet at the same time.

ASTM G24-2021 Standard Test Method for Exposure Tests in Sunlight Through Glass

Radius
1.1 This code describes procedures for exposing various materials to daylight filtered through glass in passively ventilated and unventilated enclosures. For exposure under glass enclosures with forced air circulation, see Practice G201.

1.1.1 This practice does not apply to corrosion testing of bare metals.

1.2 For direct exposure, see Practice G7.

1.3 This practice is limited to methods of exposure. The preparation of samples and the evaluation of results are covered in various standards for specific materials.

1.4 Two types of exposure cabinets can be used for exposure according to this practice.

1.4.1 Type A – Cabinets that allow passive ventilation of specimens exposed behind glass.

1.4.2 Type B – Enclosed cabinet, externally painted black, does not provide ventilation for specimens exposed behind glass. Exposure using a B-cabinet is often referred to as “black box exposure under glass”.

1.5 Type A exposure of this practice is technically similar to method B of ISO 877-2.

1.6 Units – Values expressed in SI units should be considered standard values. The values given in parentheses after the SI unit are for reference only and are not considered standard values.

1.7 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, health and environmental practices and to determine the applicability of regulatory restrictions prior to use.

1.8 This international standard is based on internationally recognized standardization principles established in the Decision on Principles for the Development of International Standards, Guidelines and Recommendations issued by the WTO Committee on Technical Barriers to Trade.