ISO 18930 was confirmed in 2011 as a new International Standard test method for accelerated weathering. It is a four-segment test cycle that simulates day, night, rain, and condensation. The spectral power distribution of the light source was created based upon a tolerance band around the CIE 85 spectral power distribution of sunlight. A round-robin test has been conducted to validate the new method. This is the first data published to substantiate the use of ISO 18930.Acceleration factors and Pearson correlation coefficients are presented for nine worldwide outdoor locations, along with examinations of lab-to-lab and replicate reproducibility. The results validate that ISO 18930 is a valid and versatile accelerated weathering test method that is applicable to a large range of materials. Due to the dark cycle segment with water spray followed by a light cycle segment at elevated temperature, it is believed that this cycle may perform better than ASTM G155, Cycle 1 for some materials that are brittle, porous, or hygroscopic. ISO TC42 WG-5 has also recommended that an ISO Technical Report with a detailed data analysis be written to document the results of this round robin test.