Color measurement is an indispensable technology for quality control and quality estimation in color industry.
Light belongs to the electromagnetic waves. Within their spectrum, the human eye captures visible light in the range between about 380 nm and 700 nm. In addition to brightness ( Brightness Meter ) and darkness perception the eye captures three different color ( Colorimeter ) stimuli: blue, green and red. The color impression is achieved by addition of these three stimuli in the brain. From this it follows that any color can be composed by adding red, green and blue.
Formation of the color impression
The color impression an observer gets from a sample depends on three interrelated factors.
1. Light source
Different light sources (e.g. daylight, filament lamp) feature different intensities of their individual spectral components and therefore produce different color impressions.
The composition of the sample defines the components of reflection, absorption and refraction and thus the entire spectral composition of the reflection spectrum.
Different sensitivities of the three light-sensitive receptors on the retina convey different color impressions with different observers.
For the illumination ( Luminance Meter ) conditions for color measurement to be clearly defined, the spectral composition of the light sources must be known and be included in the measurement as a constant value. As different fields of application of a measuring instrument require different illuminance conditions, the spectral composition of some typical light sources was analyzed and defined as so-called standard illuminants.
Standard illuminant A = standardized filament lamp light (2856 K)
Standard illuminant C = medium daylight, without UV component (6750 K)
Standard illuminant D65 = medium daylight, with UV component (6500 K)
Standard illuminant F2 =CWF
Standard illuminant F11= fluorescent lamp
The D65 standard illuminant is very often used. It corresponds to the spectral composition of medium daylight and also includes the corresponding UV component of this light. The color of objects looks different in different light sources, therefore the type of light source must always be indicated.