Color rendering and temperature

The color rendering ability of the light source is called the color rendering, which is with the same color reference or reference light source (incandescent lamp or sun light) to compare the object color appearance.The spectral content emitted by light decides the light color, but the same color can be made by many, a few or even only two monochromatic lights. The color rendering of each color is also very different. The light of a wider spectrum is more likely to provide a better color rendering quality. 

When the light spectrum is very small or the lack of main wave which is reflected by an object under the reference light, it will make the color of the obvious shift color. The greater the degree of color is, the worse the color rendering is. The color rendering index coefficient (Kaufman) is still a common method to define the color rendering property of the light source.

There are two kind of color rendering

Faithful color: it can accurately show the original color of the material and needs to use the color rendering index (Ra) high light source. When its value is close to 100, the color rendering is the best.

The effect color: Additive color method can be used to enhance the color rendering effect when highlighting the specific color and showing the beautiful life. The using of low color rendering lights can make the red more vivid; the medium color rendering lights can make the blue with a cool feeling; the high color rendering lights can make the object a cold feeling.

The relationship between color rendering index and color rendering property

When the light spectrum is very small or the lack of main wave which is reflected by an object under the reference light, it will make the color of the obvious shift color. The greater the degree of color is, the worse the color rendering is. The color rendering index coefficient (Kaufman) is still a common method to define the color rendering property of the light source.

The color rendering index of incandescent lamp is defined as 100, which is considered as an ideal reference source. The system uses eight chroma medium standard color sample to test and compare the color deviation degree under the inspecting lights and the same color reference, which aims to measure the color index. The average deviation value is Ra20-100 with 100 as the highest. The bigger the average color difference is, the lower the Rr value is. The light less than 20 is generally not suitable for general use.

Index (Ra) rating  color rendering property  general application  90-100 1A  applied to the occasions of precise color contrast.

80-89 1B  Occasions where color is needed to judge correctly

60-79 2   Occasions where color is needed medium rendering

40-59 3  Occasions where color rendering is required is low and color difference is small.

20-39 4   Ooccasions without specific requirements of color rendering

CT-color temperature

The same color of light emitted by the light source color and blackbody radiation at a certain temperature, the temperature of the blackbody called the color temperature of the light source which expressed by absolute temperature K. Blackbody radiation theory is established on the basis of thermal radiation, so the spectral power distribution of thermal radiation light source like incandescent lamp is close to that of blackbody in the visible region. They are continuous spectrum. The color temperature can be used to describe the color characteristic of the kind of light source.

CCT-correlated color temperature

When the color emitted by a light is close to that of a black body at a certain temperature, the temperature of the blackbody is called the CCT-correlated color temperature which unit is K. Because the gas discharge light is a non-continuous spectrum and the continuous spectrum of the blackbody radiation cannot be completely consistent, correlated color temperature is used to describe its color characteristics. The light which its color temperature (the correlated color temperature) is less than 3300k gives a warm feeling. The light which is more than 5300K gives a cold feeling. Usually people who live in high temperature area will adopt the light which higher than 4000K while people who live in low temperature area region adopt the light which is below 4000K.

Ra-color rendering index

Both the sun light and the incandescent lamp are continuous spectrum. In the wavelength of visible light (380nm-760nm) range, they include red, orange, yellow, green, green, blue, purple and other colors. The object illuminated by them shows its true color. When the object illuminated by the gas discharge lamp in the non-continuous spectrum, its color will has different degree of distortion. The degree of the true color of the object is called the color rendering of light. In order to make a quantitative evaluation of the color of the light source, the concept of the color rendering index is introduced. The color index of the standard light source is 100, and the color index of the other light sources is less than 100. Ra is used to express color rendering index. The greater the value of Ra is, the better the color rendering of the light is.