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evaluation method of colorability of led fluorescent replacement lights light source

The color can not be separated from the lighting, only in the light under the object can show the color, and the color of light on people’s psychology has a very big impact.

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

Newton in 1664 with a prism to disperse the white sunlight into different shades of the spectrum, laying the light color of the physical basis. In 1860 Maxwell with different intensity of red, yellow, and green light out from the white light has been to a variety of colors of light, laid the basis for three color chromaticity. On this basis, the 1931 International Commission on Illumination established CIE colorimetric system, and continue to improve. The CIE chromaticity system is now widely used to quantitatively express the color of light.

Color is inseparable from lighting, only in the light of objects can 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 good description in Chapter 5 of his book “Visual and Visual Environment”.

In a different light source, the same object will show a different color. For example, green leaves in the green light, there are bright green, in the red light near black. Thus, the light source on the color of the object appears to play, plays an important role. Light source in the irradiation, the ability to fully show the ability to illuminate the color, known as the color of the light source.

In 1965, the International Commission on Illumination recommended in the CIE color system, the general color rendering index Ra to describe the color of the light source. The general color rendering index Ra has been used successfully, has been widely accepted by the lighting industry, but there are also some problems, this article will light color rendering evaluation methods, as well as in recent years to make an introduction.

1, the general color rendering index Ra

The method for evaluating the color rendering property of the light source is desired to be simple and practical. However, simple and practical are often two contradictory requirements. In the CIE color system, the general color rendering index Ra is such a compromise of the product: it is relatively simple, only need a value within 100, you can express the color rendering performance of the light source, Ra = 100 is considered the most ideal color .

But sometimes people do not feel that way. For example, under the incandescent light of the leaves, does not look too bright. Where is the problem? Let us discuss what is the general color rendering index.

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

In fact, in our daily lives, often in the test of color rendering. Many people have such experience, careful lady in the mall to buy clothes, often to the outdoor sunlight and then look at its color. She did this, in fact, is to test the color of the mall light source: take a look at the same piece of clothing, lighting in the mall lighting and lighting in the sunlight, the color of the clothes What is the difference. Therefore, to describe the color rendering of the light source, two additional elements are required: daylight (reference light source) and clothes (colored object).

Xiaobian give a chestnut: I am a friend, home decoration to buy wood flooring.

She saw in the shop the color of the wood floor is like this:

Sent to the home when instalLed fluorescent replacement lights, the sun came in and found that this is the way:

She could not help feeling: the original show room lights like a woman make up, after unloading the makeup is not the original face!

In the CIE color system, in order to determine the color of the light source to be tested, we must first select the reference light source, and that in the reference light irradiation, the illuminated object color can be the most complete display. The CIE color system stipulates that when the correlated color temperature of the source to be measured is less than 5000K, the closest black body with the color temperature is used as the reference light source. When the correlated color temperature of the source to be measured is more than 5000K, the closest D light source is used as the reference light source. Where the D light source is a series of color coordinates which can be expressed numerically and correlated with the color temperature of the daylight.

After selecting the reference light source, you also need to select the colored object. Due to the variety of colors, you need to select a set of standard colors so that they fully represent commonly used colors. The CIE color system selects eight colors, which have a variety of hues and medium brightness values ​​and saturation.

In the u v color system, the specific color rendering index Ri of the color plate can be obtained by measuring the color shift ΔEi of each standard color plate under the irradiation of the source to be measured and the color coordinate of the reference light source.

Ri = 100 4.6? Ei

The average color rendering index Ra is obtained by averaging the special color rendering index Ri of the eight standard color plates. Visible light source of the general color rendering index Ra maximum value of 100, that the color of the best light source.

2, the general color rendering index Ra limitations

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

First of all, the color is a subjective feeling, not the inherent properties of the object, it with the lighting conditions, observer, irradiance, illumination, the surrounding objects and observation angle and so on, there is no so calLed fluorescent replacement lights “true color.” However, since in the CIE system, Ra has been defined as having a maximum value of 100 in approximately blackbody radiation, the lamp manufacturer has consciously designed the bulb to be as close to the blackbody or daylight as possible when illuminating the object with it. This means that the spectral distribution of the light source and the blackbody or daylight deviation, the color rendering index will decline. For example, a white Led fluorescent replacement lights composed of three monochromatic Led fluorescent replacement lightss, red, green and blue, is sometimes not necessarily bad in color rendering when its general color rendering index Ra is low.

But in fact, the researchers Judd, Thorntou and Jerome have confirmed that people do not necessarily like most of the reference light source CIE lighting color. Such as the previously mentioned with very low color temperature of the incandescent light green leaves, not necessarily the best choice. It is specified that the color rendering index is the optimum value Ra = 100 in the case of blackbody or daylight irradiation.

The reference light source specified by CIE is the blackbody or daylight which is closest to the correlated color temperature of the light source to be measured. They are the light source of continuous spectrum of radiation and have spectral components of a plurality of colors. When the color temperature at 6500K, the long and short wave spectral power distribution is more balanced, as a reference source should be more reasonable. But when the color temperature below 400K, the spectral power distribution is seriously asymmetric, blue short wave spectral power is much smaller than the red long wave spectral power, its color bias red, as a reference light source in doubt.

In the CIE color system, 8 standard color plates are in the medium lightness and color saturation, in the u ~ v system for equidistant intervals. For indoor lighting, they can be considered fully representative of a variety of commonly used colors. However, in outdoor lighting, there are often a number of colors with high color saturation, which 8 standard color plate has been unable to fully represent the commonly used colors.

Many scholars believe that the standard number of plates is too small, the general color rendering index is another shortage. Although the CIE has 9 14 color saturation of the higher 6 color plates, but they are not included in the general color rendering index Ra. In the lighting practice, known as 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 was rejected because it made the calculations too complicated. At present, the computer is widely used, it seems that this proposal has to reconsider.

Because of the two major problems in the evaluation of the color rendering of light sources, many other methods of evaluation have attracted wide interest and will be briefly described by the author.

3, Fulletti index Rf

Studies have shown that people tend to remember the color of familiar objects, and remember its vivid, high saturation color. This memory color and favorite color are often consistent, and tend to shift to the direction of high saturation. Such as the color of people’s memory color, tend to shift in the red direction, leaves the color shift to the green direction. Obviously different from the Ra method in CIE.

Rf is in fact the amendment to Ra, this amendment includes two aspects:

First, Rf = 90 is defined under the illumination of the reference light source, and Rf = 100 only under the hypothetical “perfect light” illumination.

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

At this time, the “perfect light source” refers to it in the irradiation, the standard 10 color can shift the color to the favorite direction of the light source.

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

Rf of the standard method and Ra similar, but there are two different:

1, for each standard color plate, the reference light color coordinates need to be adjusted, that is, according to the experiment to determine the “perfect light” color coordinates. Then, in the light source to be tested, the color difference of each color plate is with its corresponding “perfect light source” compared to get.

2, in the calculation of Rf, the average color difference of 10 color plates, but the weight of each palette different. Color plate 13 is the color, the weight is 35%, 2 is 15%, 14 is 15%, the rest is 5% each. In particular, the importance of skin color is emphasized here. Rf of the source to be measured can 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 favorite color concept presented in the previous section, we define the color preference index CPI = 100 under D65 illumination.

So the light source of the CPI can be measured so:

Under the illumination of the source to be measured, calculate the difference between the color coordinates of the eight standard color plates and the color coordinates of the favorite color, and find the average of the vector sums (): CPI = 156 7.18 ()

The above calculations were carried out in the CIE UV colorimetric system.

Although CPI and Rf are using the concept of 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, the calculation of Rf, the weight of the different color blocks, while the CPI to take the same weight

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

Finally, to point out that Rf and CPI index of the two researchers, are used to determine the favorite color experiment, and in the experiment using a daylight color lighting. There is now evidence that favorite colors are related to the correlated color temperature of 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)

Ra, Rf or CPI to describe the color rendering of the light source, the reference light source must be the same color temperature of the light source to be measured. Color discrimination index CDI (color discrimination index) to overcome this limitation.

The proposed index is based on the assumption that the ability to distinguish colors under the illumination of a certain source of light is stronger and the color rendering of the light source is better. In a light source illumination, 8 standard color plate in the CIE UV chromaticity diagram, surrounded by the area:

GA = 0.5Σ (UiVj UjVi) i, j = 1,2, …, 8; i? J

evaluation method of colorability of led fluorescent replacement lights light source

In the C light source illumination, the area GA = 0.005, defined at this time CDI = 100, so in the light source under test, the color resolution index:

CDI = (GA / 0.005) x 100

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6, concluding remarks

From the above discussion, we can see that there are many evaluation methods of the color rendering of light source, and in the continuous development and perfection, this article is only a part of them, they have advantages and disadvantages.

Even if the current general use of the general color rendering index Ra, there are still many shortcomings.

Its main drawback is the choice of reference light source: the reference light source is a continuous spectrum of light source, use it as a standard to measure the spectral discontinuity of the light source is not very appropriate. The color temperature of the reference light source must be close to the correlated color temperature of the light source to be measured, and in fact, the color temperature itself has a great influence on the color rendering property for a certain lighting operation. This method restricts the color temperature of the light source only, Conditions.

Its second drawback is the choice of standard color palette: for indoor lighting, can be considered 8 standard color plate has been able to fully represent the various commonly used colors. However, in outdoor lighting, the higher the color saturation of some colors, can not fully representative of common colors.

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