An outdoor exposure-testing program for architectural coatings was conducted in Tsukuba from 1987-1997. Observed gross retention of samples set horizontally, 5-deg. south and 30-deg. south was on average severer than that of 90-deg. south, while the conditions of 90-deg. north are more moderate. The lightness of white samples decreased during the early part of the fi rst year and was almost constant, thereafter. Delta L * of 90-deg. south and 90-deg. north is smaller than that of horizontal,

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... eg. south and 30-deg. south. Koike and Tanaka's equation is a more appropriate analytical method regarding the weatherability of exposed paints and coatings than the conventional system, which uses solar UV.