Luxsky Lighting Co.,Limited

Tel:0086-755-82590839
Contact US
Address: C&H Building, Wanda Industrial Park, Shiyan Town, Bao'an district, Shenzhen City, China
TEL: +86-755-82590839
+86-755-33654459
FAX : +86-755-33654451
Home > Exhibition > Content
Is Ra = 100 really the best color?
- May 17, 2017 -

Color is one of the feelings of people, it is always with the observer's personal subjective experience. Everyone to see a color after the feeling that others are difficult to know. So the color of the study is always full of mysterious imagination. At the same time, the color and make the world become colorful, visual arts, image display and transmission, textile printing and dyeing, color printing, etc., are inseparable from the color of the study. So the color of the study, the color of the objective quantitative description, as many scientists to study the object.

Newton in 1664 with the prism to white sunlight scattered into different colors of the spectrum, laid the physical basis of light color. 1860 Maxwell with different intensity of red, yellow and green light with the light from the white light has been to a variety of colors of light, laid the basis for three-color chromaticity. On this basis, in 1931 the International Commission on Illumination established the CIE chromaticity system, and constantly improve. Today CIE chromaticity systems have been widely used to quantitatively express light colors.


LED COLOR.gif


The color can not be separated from the lighting, only in the light of the object is likely to show the color, and the color of light on people's psychology has a very big impact. Professor Yang Gongxia of Tongji University has made a very wonderful description in his fifth chapter, "The Visual and Visual Environment".

The color can not be separated from the lighting, only in the light of the object is likely to show the color, and the color of light on people's psychology has a very big impact. Professor Yang Gongxia of Tongji University has made a very wonderful description in his fifth chapter, "The Visual and Visual Environment".

For the sake of simplicity, we only discuss the main constituent methods of the general color rendering index Ra, without discussing its specific calculation method.

 

In fact, in our daily life, we often check the color of the light source. Many people have this experience, careful ladies in the mall to buy clothes, often also to the outdoor sun and then look at its color. She did so, in fact, is to test the color of the light source of shopping malls: take a look at the same piece of clothing, under the lighting in the mall light and under the lighting of the sun, the color of the clothes are different. So describe the color of the light source, the need for two additional elements: daylight (reference light source) and clothes (colored objects).

 

In the CIE color system, in order to determine the color rendering of the light source to be measured, first select the reference light source, and that the reference light source irradiation, the color of the object can be the most complete display. The CIE color system stipulates that the blackbody with the closest color temperature should be used as the reference light source when the relevant color temperature of the light source is less than 5000K when the relevant color temperature of the light source is less than 5000K. Here D light source is a series of color coordinates can be expressed in digital, and with the color temperature of the daylight.

After selecting the reference light source, you also need to select colored objects. Due to the diversity of colors, you need to select a set of standard colors that make them fully representative of the commonly used colors. CIE color system selected eight colors, they have a variety of colors, but also has a moderate degree of brightness and saturation.

In the u-v color system, the specific color rendering index Ri of the color palette can be obtained by measuring the difference between the color coordinates of each block and the color coordinates ΔEi under the irradiation of the light source to be measured and the reference light source. (Ri = 100-4.6ΔEi)

 

The average color rendering index Ra is obtained by taking the arithmetic average of the special color rendering index Ri measured by eight standard color plates. The maximum color rendering index Ra of the visible light source is 100, and it is considered that the color of the light source is the best.

2, the general color rendering index Ra limitations

 

Although the general color rendering index Ra is simple and practical, it exhibits a serious shortage in many respects.

 

First of all, the color is the subjective feeling, not the inherent properties of the object, it is with the lighting conditions, observers, irradiance, illumination, the surrounding objects and observation angle, etc., there is no so-called "real color."

 

However, since the Ra has been defined to be the highest value of 100 in the CIE system, the bulb manufacturer has intentionally designed the bulb so that the color rendering when irradiating the object is as close as possible to the case of blackbody or sunlight. This means that the spectral distribution of the light source deviates from the blackbody or the daylight, causing the color rendering index to fall. For example, with red, green, blue three monochrome LED composed of white LED, when its general color rendering index Ra is low, its color is sometimes not necessarily bad.

But in fact, the researchers Judd, Thorntou and Jerome have confirmed that people do not necessarily like the CIE's specified reference light when illuminating the color. For example, has been mentioned earlier with very low color temperature incandescent light green leaves, not necessarily the best choice. It is assumed that the color rendering index is the optimum value Ra = 100 in blackbody or sunlight.

The reference light source specified by the CIE is the bold or daylight closest to the correlated color temperature of the light source to be measured, and they are light sources that radiate continuous spectrum and have spectral components of multiple colors. When the color temperature at 6500K, the length of the short-wave spectral power distribution is more balanced, as the reference light source should be said to be more reasonable. However, when the color temperature below 4000K, the spectral power distribution is seriously asymmetric, blue short-wave spectral power is much smaller than the red long-wave spectral power, the color bias red, as a reference light source in doubt.

In the CIE color system, eight standard swatches are in moderate and color saturation, equidistant intervals in the u-v system. They are for indoor lighting, can be considered to be able to fully represent a variety of commonly used colors. But in the outdoor lighting, there are often some color saturation of the higher color, the eight standard color palette can not fully represent 

the commonly used color.

 

Many scholars believe that the standard color plate number is too small, is the general color rendering index of another deficiency. Although the CIE also has 9 colors with a high saturation of 9-14, they are not included in the general color rendering index Ra. In the practice of lighting, people are familiar with the color of the skin, leaves, food, etc., their color is extremely important, but they are excluded from the general color rendering index.

 

Seim had proposed using 20 standard swatches, but this would be rejected because it would make the calculations too complicated. At present, the computer is widely used, it seems that this proposal has to reconsider.

 

Many other evaluation methods have aroused broad interest due to the existence of these two problems in the evaluation of color rendering of light sources. This article will give a brief introduction to the author's knowledge.

3, the husbandley index Rf

Studies have shown that people tend to remember the colors of objects that are more familiar, and are reminiscent of its vivid, high saturation color. This memory color is often consistent with the favorite color, and tends to shift to a high degree of saturation. Such as people's color of the memory, tend to shift to the red direction, leaf color to the green direction offset. Obviously different from the Ra method in CIE.

 

Rf is in fact a correction to Ra, which includes two aspects:

First, Rf = 90 is defined under the illumination of the reference light source, and Rf = 100 only under the imaginary "perfect light" illumination.

Second, the choice of 10 standard color plate, that is, in addition to the original standard color card 1-8, but also with No. 13 No. 14 two color plates, corresponding to the skin color and leaf color.

 

At this time, "perfect light" refers to it in the irradiation, can be 10 standard color palette color to the favorite direction of the light source offset.

 

Thus, for each standard color plate, the corresponding "perfect light source" color coordinates are different, can be determined by the experiment. This also shows that such a "perfect light source" can only be hypothetical.

 

Rf's measurement method is similar to Ra, but there are two different points:

1. For each standard palette, the color coordinates of the reference light source need to be adjusted, that is, according to the experiment to determine the "perfect light" color coordinates. Then, when the light source is illuminated, the color difference of each color plate is compared with its corresponding "perfect light source".

2. When calculating Rf, take the color difference of 10 patches, but the weight of each patch is different. 13 color plate is skin color, weight is 35%, 2 is 15%, 14 is 15%, the rest is 5% each. This emphasizes the importance of skin color. The Rf of the light source to be measured may be higher than the reference light source Rf = 90 but less than 100.

4, color preference index (CPI)

 

Color preference index CPI (color preference index) using the previous paragraph of the favorite color concept, defined in the D65 light source lighting, color preference index CPI = 100.

 

So the CPI of the light source to be measured can be obtained by calculating the difference between the color coordinates of the eight standard patches and the color coordinates of the favorite colors and the average value of the vector sum (CPI = 156) -7.18 ()

 

The above calculations are performed in the CIE's UV chromaticity system.

 

Although CPI and Rf are using the concept of the most favorite color, but the two are very different:

1. In the calculation of Rf, with 1-8 and 13, 14 a total of 10 standard color plate, and CPI only 1-8 standard color plate

2. Technology Rf, the color difference (ΔE) take the experimental value of 1/5, while the CPI to take the original experimental value

3. When calculating Rf, the weights of the patches are different, and the CPI takes the same weight

4. According to the definition of Rf maximum of 100, while the maximum value of the CPI is 156

 

Finally, to point out that Rf and CPI two indicators of the researchers, are used to determine the color of the experiment, and in the experiment is used in daylight lighting. There is now evidence that the color of love is related to the color temperature associated with the light source. So the use of Rf and CPI to constant color rendering, only for high color temperature light source.

5, color resolution index (CDI)

 

Use Ra, Rf or CPI to describe the color rendering of the light source. The reference light source must have the same color temperature as the light source to be measured. The color discrimination index CDI (colourdiscrimination index) overcomes this limitation.

 

The index suggests that, based on the assumption that the ability to distinguish color from the illumination of a certain light source is, the better the color rendering of the light source. In the case of a light source, the area enclosed by the eight standard swatches in the CIE's UV chromaticity diagram is: GA = 0.5Σ (UiVj-UjVi) i, j = 1,2, ... 8; i j The

 

In the C light source illumination, the area GA = 0.005, defined at this time CDI = 100, so in the light source to be illuminated, the color index is: CDI = (GA / 0.005) × 100.

From the above discussion, we can see that there are many methods to evaluate the color rendering of light source, and in the development and perfection, this article describes only a part of them, each of which has advantages and disadvantages. Even now widely used in general color rendering index Ra, there are many shortcomings.

Its main drawback is the reference light source selection: the reference light source is a continuous light source, using it as a standard to measure the spectral discontinuity of the light source, not very appropriate. The color temperature of the reference light source must be close to the color temperature of the light source to be measured, and in fact, for a certain lighting operation, the color temperature itself has a great impact on the color rendering, this method can only be used in the light source color temperature has been determined Under conditions of use.

 

Its second drawback is the choice of standard swatches: for indoor lighting, can be considered 8 standard color palette has been able to fully represent a variety of commonly used colors. But in outdoor lighting, the color saturation of some of the higher color, can not fully represent the commonly used color.


LED LINEAR .jpg


best selling products: LED panel lights, LED waterproof panel light,

LED linear high bay, 


www.luxsky-light.com