Some photographic situations require specific colour corrections. For example, when shooting daylight film under fluorescent lighting, some magenta correction is needed in order to remove the greenish tint that would otherwise appear. The amount of colour correction required is most accurately measured via a colour temperature meter. Colour Compensating filters are available in the three primary colours: Red, Green, and Blue; and in the three secondary colours: Cyan, Magenta, and Yellow. A typical designation for one of these filters is CC30M. The ""CC"" stands for Colour Compensating. The ""30"" stands for a density of 0.30 and the ""M"" is for magenta. Lee colour compensating filters are made in the following increasing densities: 0.025(CC025), 0.05(CC05), 0.10(CC10), 0.15(CC15), 0.20(CC20), 0.25(CC25), 0.30(CC30), 0.40(CC40), 0.50(CC50). You can sandwich as many as three Lee polyester filters together without a noticeable loss of image quality.