What is color rendering/color rendering index (CRI/Ra)
1. What is color rendering and color rendering index (Ra/CRI)?
(1) Intuitive understanding
The picture above shows the colors of the same pot of flowers under light sources with the same color temperature and different color rendering properties. You can intuitively feel that the better the color rendering properties (that is, the higher the color rendering index), the closer the color of the flower is to the true color.
(2) In-depth analysis
Color rendering measures the degree to which a light source presents the color of an object, that is, how realistic the color is. It is a qualitative evaluation. Light sources with high color rendering reproduce colors better, and the colors we see are closer to natural primary colors (colors under the sun); light sources with low color rendering reproduce colors poorly, and the colors we see The color deviation is also large.
Color Render Index (CRI) is currently a common method for defining the color rendering of a light source. It is used to quantitatively evaluate the color rendering of a light source. It is the relative difference between the color of an object under the measured light source and the color of the object under the reference light source. degree of compliance. The International Commission on Illumination (CIE) sets the color rendering index of sunlight as 100. The color rendering index of incandescent lamps is very close to that of sunlight, so it is regarded as an ideal reference light source.
CIE stipulates 15 test colors/standard color samples, and numbers the 15 total colors from 1 to 15 (numbers 1 to 8 are 8 natural colors, selected from the Munsell color scale, including various representative hues , they have medium chroma and lightness; numbers 9-15 are 7 test colors, including red, yellow, green, blue, European and American young women's skin color, Chinese young women's skin color, leaf green) with higher chroma. Use R1-R15 to represent the color rendering index of the light source for these 15 colors respectively. The 15 test colors are as shown in the figure below:
The special color rendering index (Ri) is the color rendering index of a light source for a selected test color sample. The special color rendering index can be calculated by using any color sample from 1 to 15 according to the needs. It is also allowed to use self-selected color samples to calculate the required special color rendering index (but the spectral amplitude and brightness factor of the selected color sample must be accurately determined) .
The general color rendering index (Ra) is the average of the special color rendering index of the light source for the 8 colors numbered 1-8 (that is, the average of R1-R8). Usually we use this value to characterize the color rendering of the light source. The higher Ra The larger, the better the color rendering of the light source.
The following table is the details of the color rendering index obtained by the semiconductor lighting network professionals' test on a certain high color rendering D50 fluorescent lamp, a certain fluorescent lamp with a "natural white" mark, and a certain LED lamp. It can be seen that different light sources have different special color rendering indexes for the same test color, and Ra is also different; the same light source has different special color rendering indexes for different test colors:
2. How to choose color rendering/color rendering index when buying lamps?
Two principles can usually be followed when choosing color rendering, namely the principle of faithful color rendering and the principle of effective color rendering.
(1) Faithful color rendering principle
The principle of faithful color rendering means that in order to correctly express the original color of an object, a light source with a high color rendering index needs to be used. In this case, the light source can be selected according to Ra. The higher the Ra, the higher the fidelity to the original color of the object. Different application sites have different requirements for faithful color rendering of light sources.
According to the different applicable venues, the International Commission on Illumination (CIE) divides the color rendering index into five categories:
| Color rendering category | Ra | color rendering | Scope of application/level of faithful color rendering requirements | Application examples |
| 1A | 90-100 | excellent | Where accurate color contrast is required | Color matching, color inspection, art galleries, museums |
| 1B | 80-89 | good | Places where correct color judgment is required | Factories for printing, painting, fiber and precision work; residences, hotels, restaurants |
| 2 | 60-79 | general | Where medium color rendering is required | Factories for general operations such as mechanical and electrical assembly, surface treatment, and control rooms; offices and studies are also allowed |
| 3 | 40-59 | Poor | Places with low color rendering requirements | Mechanical processing, heat treatment, casting and other heavy industrial factories, outdoor streets |
| 4 | 20-39 | very poor | Places with no specific requirements for color rendering | Warehouse, building metal warehouse, outdoor road |
(2) Principle of effect color development
The principle of effect color rendering refers to the selection of a specific color rendering index in order to clearly emphasize a specific color and express a beautiful life in special scenes such as meat product windows. In this case, usually on the premise of ensuring that Ra meets the requirements, it is necessary to The color of the illuminated object increases by the corresponding special color rendering index.
Example 1: For the lighting source of meat product windows in supermarkets and stores, the R9 color rendering index is particularly important. Meat is usually reddish, and a high R9 can make the meat look fresher and more delicious.
Example 2: For occasions such as studios and photo studios where skin color needs to be reproduced realistically, the R15 index of the lighting source must not be low.
3. Extend reading
(1) Color rendering index (Ra) of common light sources
| Incandescent lamp, halogen lamp | Xenon lights | Fluorescent lamp | dysprosium lamp | LED light | Metal halide lamp | sodium thallium indium lamp | High pressure mercury lamp | HPS |
| 95-100 | 95-98 | 51-95 | 80 and above | 70-85 | 65-95 | 60-65 | 22-51 | 20-30 |
illustrate:
a. The theoretical color rendering index of incandescent lamps is 100, but in actual life there are many types of incandescent lamps with different applications, so their Ra values are not completely consistent. It can only be said to be close to 100, which is the lamp with the best color rendering. . However, due to low light efficiency, insufficient energy conservation and environmental protection, it has gradually withdrawn from the stage of history.
b. Although the color rendering of LED lamps is not as good as that of incandescent lamps, they are currently a more popular light source because they are energy-saving and environmentally friendly.
(2) Color rendering and health
If you are exposed to a light source with poor color rendering for a long time, the sensitivity of the cone cells of the human eye will also decrease. The brain will intentionally or unintentionally concentrate more on distinguishing things, which can easily cause eye fatigue and even cause myopia.
The "Hygienic Standards for Lighting and Lighting in Classrooms of Primary and Secondary Schools" states that the color rendering index of classroom lighting sources should not be less than 80. The color rendering index of classroom lighting that is too low affects the students' eyesight to recognize the color of objects, so that objects cannot show their true colors. If this situation continues, it will lead to the decline and decline of color discrimination ability, resulting in students' color blindness and color weakness. and other serious vision problems and eye diseases.
(3) Color rendering and illumination
The color rendering index of the light source and the illumination together determine the visual clarity of the environment. Research shows that there is a balanced relationship between re-illumination and color rendering index. The results obtained from extensive experiments are that an office illuminated with a lamp with a color rendering index Ra>90 is more satisfactory in terms of appearance than an office illuminated with a lamp with a lower color rendering index (Ra<60). Can be reduced by more than 25%.
