Colour Reproduction and Color Rendering Index

Light and color determine the climate atmosphere of a room. For our well-being, it is important that the colors of the environment and human skin are reproduced as realistically as possible.

If one’s skin color appears pale and colorless, it is not because of the cool light color of a lamp, but rather because of its poor color rendering quality. This property of a light source describes how naturally illuminated faces or objects appear in their light.

Good color rendering is generally an important quality feature of artificial lighting – and is indispensable in some areas, such as in restaurants, museums, or when evaluating color samples. The color impression is determined by the interaction between the color of the objects under consideration (= their spectral reflectance) and the spectral composition of the light. So we always perceive objects in daylight as “natural”. This is not surprising, because the light of the sun combines all spectral colors in its spectrum. If, on the other hand, an object is illuminated with a dominant light color, for example, blue, it appears pale, cool and often has a different color.

“Experience values” are saved

From the experience of everyday life, a number of body colors are known to people, which may look different depending on the lighting, but for which there are certain “experience values”. For example, the color of human skin is saved in daylight.

If a spectral color is missing in artificial light or some of the lamp spectrum are overemphasized, the skin color appears a little different, but based on experience, it is still “natural”. In contrast, there may be large deviations for colored materials for which there is no “empirical value” or if certain spectral colors are overemphasized in the light of a lamp.

Color rendering index Ra

The color rendering index was developed to describe the color rendering qualities. The best Ra value is 100: it naturally reproduces all colors. The lower the Ra value, the worse the colors of the illuminated object are rendered.

The color rendering properties are assessed using the so-called test color method. It is based on 14 test colors that are dominant and defined in the environment, each of which is viewed under a specific reference light source (= with Ra 100) and the light source to be tested.

The differences in color appearance are assessed using a mathematical formula. The smaller or greater the deviation of the color rendering, the better or worse the color rendering property of the tested light source.

At least Ra 80 for interiors

What kind color rendering of the LED lighting fixtures shall we use? Only light sources with at least Ra 80 should be used indoors – especially at workplaces.

LEDs are energy-saving and durable: Depending on their type and quality, they now reach values of up to Ra 98 – more than fluorescent or energy-saving lamps offer.

If you have any questions about LED lighting, welcome to contact us directly.

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