color course

LIGHTING AND ILLUMINANTS

- If you have only one wavelength of light in the visual spectrum, you will only see one color. Adding other wavelengths changes the color as the light mixes. Light sources, that is "real" lights, such as sunlight, incandescent, tungsten, and fluorescent, have different balances of wavelengths of light. As you change the mix of light, you will introduce additional light energy to illuminate the object, which has the effect of changing the colored appearance

The most important light source that we deal with in color is the light from our sun, which we call daylight.
The balance of light energy varies greatly depending on the place on earth relative to the sun, the time of day, cloud cover, air pollution, and season of year. On the average, daylight is a fairly balanced light source that is nearly white. The curve that is shown represents the relative amount of energy at each wavelength in average midday light in early summer in the Northern Hemisphere.


The spectral data that represents a type of light source is referred to as an illuminant. Tables of data are published by CIE for many types of illuminants. (CIE is the Commission International De l'Eclairage, an international organization that publishes standards in the color field.) The most important illuminants for color computer calculations are Average Daylight "D", Incandescent "A" and Fluorescent "F." The illuminant data is entered in the color computer with program calculations to provide the ability to predict how a color will appear under different types of lighting. Often a number is associated with an illuminant to identify the specific term. For example, D65, D50, and D75 are all daylight illuminants of different color temperature. Each has a specific definition and use.

DAYLIGHT

TUNGSTEN

FLUORESCENCE

The color balance of different kinds of light will change the way an object looks. If you have two objects that look the same in one type of light, but look different in another type of light, they are referred to as a "Metameric Pair." This is caused by the change in the light balance relative to different colorants in the two objects. A good example would be a paint sample matched to a print sample, a plastic sample, or textile. All materials with different colorants in them are metameric and will never be a perfect match in all types of light. This is why it is important to visually judge colors in controlled light booths.

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Color booth to eliminate outside lighting effects and to display samples under daylight tungsten and fluorescent light.

Color booths eliminate outside lighting effects and display samples under daylight tungsten and fluorescent light.

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