Let’s Explore The Secrets of CRI!

1,833 Published by admin 11 27,2018

What is CRI?

It refers to the measure of the degree of color conformity when objects are illuminated by the light source and by the standard light source (usually using sunlight as the standard light source), that is, the degree of color fidelity.
In terms of Ra, the maximum is 100. When there is little or no main wave reflected by the object under the reference light source in the light source spectrum, the color difference will be obvious. The greater the color difference, the worse the color rendering of the light source. The color rendering index coefficient is still a common method to define the color rendering evaluation of light sources.

5500K white light is 100 index, other light is not 100 as long as it is not white, the darker the color index is, the lower the color index is.

Faithful Color Rendering

A light source with high color rendering index (Ra) should be used to correctly represent the original color of the substance. Its value is close to 100, and its color rendering performance is the best.

Effect Color Rendering

We should clearly emphasize the specific color, and the life of expressing beauty can use the method of adding color to strengthen the effect of color rendering. Low color temperature light source irradiation can make the red more bright; medium color temperature light source irradiation can make the blue cool; high color temperature light source irradiation can make the object feel cold.

Color Rendering Index

The 14 colors stipulated by CIE (International Lighting Commission) and the Asian women’s skin colors added to China, there are 15 different colors. They were labeled as R1, R2, R3… R14 and R15, respectively. R1, light grey red; R2, dark grey yellow; R3: saturated yellow-green; R4, medium yellow-green; R5, light blue-green; R6, light blue; R7, light purple blue; R8, light red-purple; R9, saturated red; R10, saturated yellow; R11, saturated green; R12, saturated blue; R13. skin color; R14, white leaves; R6, light blue; R9, light purple, saturated red; R9, saturated red; R10, saturated yellow; R11, saturated green; R12, saturated blue; R14, green; R15, yellow skin color.

Among them, R1-R8 is the typical display index, R9-R15 is the special color index, and Ra is the average color index. In particular, R9 (saturated red) is an index to judge the quality of red reproduction.
For their applications, the R9 value of lighting in studios, studios and other occasions that need to truly reproduce the color of skin or model clothes must not be low. Museums, art galleries and other places require that all colors can be restored to a high degree of authenticity, and the requirements for Ra and R1-R15 values are more stringent.

General Application of Index (Ra)

90-100 1A Excellent Places for Precise Colour Contrast
80-89 1B Places for Correct Color Judgment
60-79 2 Places requiring moderate color rendering
40-59 3 places with lower requirements for color rendering and smaller color difference
20-39 4 Poor Places without Specific Requirements for Colourability

The Measured Results of CRI:

The theoretical color rendering index of incandescent lamp is 100, but there are many kinds of incandescent lamp in real life and their applications are different, so their Ra values are not completely consistent. It can only be said to be close to 100, is the best color lighting. The Ra values of specific lamps can be seen in the table below.

(1)Incandescent lamp color temperature 2545K, color rendering index 98, R1 – R15 values are relatively high.
(2) Philips high power lamp beads, color temperature 3000K, color index Ra = 83, R9 = 20.3; color temperature 6200K, color index 72, R9 = 0
(3) The color temperature of domestic high-power lamp beads is 2269K, the color rendering index Ra = 51, R9 = 90.4.
According to the above test data, there is no necessary relationship between color rendering index and color temperature. The Ra values of other light sources are as follows: 80-94 white fluorescent lamp; 75-85 warm white fluorescent lamp; 80-90; halogen tungsten lamp; 95-99 high pressure mercury lamp; 22-51 high pressure sodium lamp; 20-30 metal halide lamp.

LED Light’s CRI

After the popularity of LED as lighting fixtures, many LED packaging factories strive to improve their color rendering index (Ra) 70-80,  and even some manufacturers claim that it is as high as 90.

However, as an important indicator of illumination color rendering, red reducibility (R9 value) has been neglected, and the R9 value of many light sources in the market is mostly negative.

So why are so many lamps R9 negative? The reason is cost. In order to make R9 value above 0, the ratio of phosphor, especially red powder, will be more strict, and the corresponding cost of lamp beads will be higher. Of course, it is not excluded that some enterprises are unwilling to add additional costs, in order to ensure light efficiency and sacrifice the obvious index, which leads to R9 value is not high. How to improve the R9 value of lamps? There are no technical barriers to upgrading R9. There are two main ways to improve R9: white light beads and red powder. But pink is very expensive. However, many packaging factories in China can not cut corners or technology, reduce the price of red powder, so this is the real situation that R9 value is mostly negative.


Therefore, when producing quality LED lamps in MECREE, we should be more professional to recognize our requirements for quality products, pay more attention to the R9 index of saturated red, and the special color development index R9-R12 of four saturated colors, red, yellow, green and blue.
In general, the visual color rendering of white LED light with lower color rendering index Ra may not be poor, on the contrary, the visual color rendering of white LED light with higher color rendering index Ra may not be good. Therefore, only when Ra and R9 have high values at the same time can the high color rendering of LED be guaranteed.
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