Value (Color Theory)

The Value (also called lightness or luminosity') of a color is a measure of how light or dark a color is while its hue is held constant.

The lightness of an object depends on the reflectance of that object. Radiances (or light) striking an object can affect the lightness; however the relationship between light striking an object and its reflectance is not linear. If the same light was radiated on two different objects, one white and the other gray, the lightness of the gray object would be less than that of the white object. .

According to subtractive color theory, a color's value is changed by adding white or black to the hue. Adding black to the hue lowers the value and creates a shade of the color while adding white to the hue increases the value and creates a tint of the color.

There are various scales that record the value of lightness. One of these scales is called the CIE lightness scale. This scale is used in Photoshop and other programs. The scale is made from, “CIE luminance by a modified cube root relationship (Yn= luminance of white):”

$$L = 116 (Y/Yn)1/3 - 16; 0.008856 < Y/Yn$$

Cartographic Application
Value is often combined with saturation to design maps using either a color or a grayscale model. Normally darker values and more saturated colors indicate more of a certain quantity on a map. Quantity can also be shown in the absence of color by delineating shades of gray. For example, a map displaying population density across a region will have higher color values and more saturation as the density becomes higher. The choice of which value to use and what it represents is left up to the cartographer.

Value may be combined with hue and/or saturation to provide more clarity or convey more information in maps. A map displaying income may employ two hues, red and green. As colors increase in value, they display distance from the mean income. Red may represent all values lower than the mean, while green represents values greater than the mean.

Suggestions regarding color value

 * Make sure there is enough variation in value for each shade or color to be clearly distinguished on the map
 * Make sure the values appropriately suggest quantity using normal patterns such as light for less of a quantity and dark for more
 * Print out a few types of maps in slightly different colors to ensure that your desired design is actually conveyed on paper as there is often a discrepancy between virtual appearance on a screen and printed maps
 * When using color, make sure to use values of one color and not a series of colors that do not indicate value well. For example, don’t use a scale that goes from blue to green to red to yellow where no one of those colors inherently suggests more or less of a quantity