1. Scope 1.1 This practice covers the basic principles and operating procedures for using enclosed carbon-arc light and water apparatus intended to reproduce the weathering effects that occur when materials are exposed to sunlight (either direct or through window glass) and moisture as rain or dew in actual use. This practice is limited to the procedures for obtaining, measuring, and controlling conditions of exposure. A number of exposure procedures are listed in an appendix; however, this practice does not specify the exposure conditions best suited for the material to be tested. Note 1--Practice G151 describes performance criteria for all exposure devices that use laboratory light sources. This practice replaces Practice G23, which describes very specific designs for devices used for carbon-arc exposures. The apparatus described in Practice G23 is covered by this practice. 1.2 Test specimens are exposed to enclosed carbon arc light under controlled environmental conditions. 1.3 Specimen preparation and evaluation of the results are covered in various methods or specifications for specific materials. General guidance is given in Practice G151 and ISO 4892-1. More specific information about methods for determining the change in properties after exposure and reporting these results is described in ISO 4582. 1.4 The values stated in SI units are to be regarded as the standard. 1.5 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 and health practices and determine the applicability of regulatory limitations prior to use. 1.5.1 Should any ozone be generated from the operation of the light source, it shall be carried away from the test specimens and operating personnel by an exhaust system.