ASTM G178-16(2023) PDF

SIGNIFICANCE AND USE 4.1 The activation spectrum identifies the spectral region(s) of the specific exposure source used that may be primarily responsible for changes in appearance and/or physical properties of the material. 4.2 The spectrographic technique uses a prism or grating spectrograph to determine the effect on the material of isolated narrow spectral bands of the light source, each in the absence of other wavelengths. 4.3 The sharp cut-on filter technique uses a specially designed set of sharp cut-on UV/visible transmitting glass filters to determine the relative actinic effects of individual spectral bands of the light source during simultaneous exposure to wavelengths longer than the spectral band of interest. 4.4 Both the spectrographic and filter techniques provide activation spectra, but they differ in several respects: 4.4.1 The spectrographic technique generally provides better resolution since it determines the effects of narrower spectral portions of the light source than the filter technique. 4.4.2 The filter technique is more representative of the polychromatic radiation to which samples are normally exposed with different, and sometimes antagonistic, photochemical processes often occurring simultaneously. However, since the filters only transmit wavelengths longer than the cut-on wavelength of each filter, antagonistic processes by wavelengths shorter than the cut-on are eliminated. 4.4.3 In the filter technique, separate specimens are used to determine the effect of the spectral bands and the specimens are sufficiently large for measurement of both mechanical and optical changes. In the spectrographic technique, except in the case of spectrographs as large as the Okazaki type (1),4 a single small specimen is used to determine the relative effects of all the spectral bands. Thus, property changes are limited to those that can be measured on very small sections of the specimen. 4.5 The information provided by activation spectra on the spectral r... SCOPE 1.1 This practice describes the determination of the relative actinic effects of individual spectral bands of an exposure source on a material. The activation spectrum is specific to the light source to which the material is exposed to obtain the activation spectrum. A light source with a different spectral power distribution will produce a different activation spectrum. 1.2 This practice describes two procedures for determining an activation spectrum. One uses sharp cut-on UV/visible transmitting filters and the other uses a spectrograph to determine the relative degradation caused by individual spectral regions. Note 1: Other techniques can be used to isolate the effects of individual spectral bands of a light source, for example, interference filters. 1.3 The techniques are applicable to determination of the spectral effects of solar radiation and laboratory accelerated test devices on a material. They are described for the UV region, but can be extended into the visible region using different cut-on filters and appropriate spectrographs. 1.4 The techniques are applicable to a variety of materials, both transparent and opaque, including plastics, paints, inks, textiles and others. 1.5 The optical and/or physical property changes in a material can be determined by various appropriate methods. The methods of evaluation are beyond the scope of this practice. 1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Note 2: There is no ISO standard that is equivalent to this standard. 1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Develop...