Different colour systems (eg. RGB, CMYK, HSL) are employed for different colour conditions depending on how the colour is created. If using projected light, then RGB (Red-Green-Blue) is the governing system. When colours are mixed with paints, pigments or inks, and applied to paper, then CMY (Cyan-Magenta-Yellow) is the colour model. Because these pure pigments are expensive, the colour Black (K), is substituted for equal parts of CMY to lower ink costs, producing the CMYK system. Another major colour model is HSL (Hue-Saturation-Lightness). This system comprises several variants substituting saturation with chroma, luminance and value etc.