5.1 This test method describes the means of determining the LRV of a tile specimen. Certain building codes require the use of materials rated by LRV. Application of this test method provides the means for rating ceramic tile. LRVs reported for ceramic tile should include reference to the observer and illuminant for which the rating is valid.

5.2 LRV is a property dependent on the overall color of a tile specimen. Control of LRV is achieved through control of color and adherence to color specifications will govern the acceptability of a product with respect to LRV. Therefore, a product cannot be judged as having an unacceptable LRV unless the color of the product is found to be unacceptable.

5.3 Mixtures of several tile products are commonly installed on a surface, requiring a means to calculate LRV for a product mix. The rating obtained for an individual tile product can be used to calculate the LRV for a product mix using the following equation:

For example, a mixture of two products is used on a surface. Two thirds of the surface area is covered by product A with a LRV of 75 %, and one third of the surface is covered by product B with an LRV of 60 % (see Fig. 2). Using the equation, the product mix is found to have an LRV of 70 %.

FIG. 2 Example of Product Mix Used on Surface

5.4 The test method described herein provides instrumental means as the basis for judging color difference. Magnitude of color difference between pairs of ceramic tile can be determined and expressed in numerical terms.

5.5 Based on interlaboratory investigation,3 color difference δE of plain-colored tile, if determined in accordance with this test method, should give excellent reproducibility with a standard deviation of not more than σ = ±0.15 units. LRV should also give excellent reproducibility when used for solid colored tile based on the relationship between LRV and either the Y tristimulus or L value. However, LRV reproducibility for multicolored, speckled, or textured surface tile will be dependent upon the degree of variation of the tile specimen, and will require a different measurement procedure to minimize the impact of the variation.

5.6 The test method requires the use of multiple illuminants for the determination of color difference between solid-colored tiles. Evaluation under incandescent, fluorescent and daylight illuminant conditions ensure the color differences calculated between a test and reference specimen account for the possible occurrence of metamerism.