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Color rendering index (CRI) of LED strips
2024-09-13 14:33:34
Color rendering index (CRI) is a commonly used parameter in the field of lighting technology. It refers to the measure of the degree to which the color of an object is consistent when it is illuminated by this light source and when it is illuminated by a standard light source (generally using sunlight as the standard light source), that is, how realistic the color is.
1.CRI definition
For lighting practitioners, color rendering index (CRI) is a commonly used term. We often see the CRI value in the data of light sources, and know that it reflects the quality of the light source in terms of color rendering.
But what does it actually mean? The CRI value helps determine what light source should be used in a lighting device. The higher the CRI value, the better, but do people know what it actually measures and how to measure it? For example, the CRI value of OLIGHT S1MINI is 90. What information does this convey? The lighting quality of the museum must be above CRI 95. Why?
To put it simply: color rendering is an important aspect for evaluating lighting quality, and color rendering index is an important method for evaluating the color rendering of light sources. It is an important parameter for measuring the color characteristics of artificial light sources. The higher the color rendering index, the better the color rendering of the light source. The better the color, the stronger the color restoration ability of the object.
The International Commission on Illumination (CIE) defines color rendering as: the effect of a light source on the color appearance of an object compared with a standard reference light source.
In other words, CRI is a measurement method of color recognition of a light source compared with a standard light source (such as daylight). CRI is a universally recognized metric and the only way to evaluate and report the color rendering of a light source. way.
The establishment of the CRI metric standard is not far away. The original purpose of establishing this standard was to use it to describe the color rendering properties of fluorescent lamps that were widely used in the 1960s, and to help users understand that fluorescent lamps with linear spectral distribution can be used in Which occasions.
2.CRI technology
Although these color swatches are carefully specified and real objects can produce the colors of these swatches, it is important to understand that the CRI values are derived entirely through calculation and do not necessarily illuminate the real color swatch with a real light source.
What we have to do is to use the measured light source spectrum to compare with the spectrum of the specified color sample, and then derive and calculate the CRI value through mathematical analysis.
Therefore, the measurement of CRI value is quantitative and objective. It is by no means a subjective measurement (subjective measurement only relies on a trained observer to judge which light source has better color rendering).
Comparisons based on color perception are also meaningful, provided that the color temperature of both the measured light source and the reference light source must be the same.
For example, trying to compare the appearance of two identical color swatches illuminated by a warm white light source with a color temperature of 2900K and a cool white light source (daylight) with a color temperature of 5600K is a complete waste of time.
They must look different, so the correlated color temperature (CCT) of the measured light source is calculated from the spectrum of the light source. Once you have this color temperature, another reference light source of the same color temperature can be mathematically created.
For the measured light source with a color temperature lower than 5000K, the reference light source is a blackbody (Planck) radiator, and for the measured light source with a color temperature higher than 5000K, the reference light source is CIE standard illuminant D.
The selection can combine the spectrum of the reference light source with each color sample to produce a set of ideal reference color coordinate points (color points for short).
The same is true for the light source under test. The spectrum of the light source under test is combined with each color sample to obtain another set of color points. If the color point under the measured light source corresponds exactly to the color point under the reference light source, we consider their color rendering properties to be the same and set their CRI value to 100.
In the color chart, the farther the color point under the measured light source is from the corresponding ideal position, the worse the color rendering and the lower the CRI value.
Calculate the color displacement of 8 pairs of color samples separately, and then calculate 8 special color rendering indexes (the CRI value of the light source for a certain color sample is called the special color rendering index), and then take their arithmetic mean, so the value obtained is CRI value.
A CRI value of 100 means that there is no color difference between any pair of color samples in the eight pairs of color samples under the measured light source and the reference light source.
3.What does the color rendering index of LED lights depend on?
The color rendering index of LED lights mainly depends on the quality and ratio of phosphors. The quality and ratio of phosphors have an important impact on the color rendering index of LED lights. High-quality phosphors can provide better color temperature consistency and smaller color temperature drift, thereby improving the color rendering index. 12
The driving current will also affect the color rendering index of the LED light. Larger driving current will cause the color temperature to drift toward higher color temperatures, thus reducing the color rendering index.
The heat dissipation system of LED also has a certain impact on the color rendering index. A reliable heat dissipation system can ensure the stable operation of LED lights and reduce light attenuation and color rendering index decline caused by temperature rise.
The spectral distribution of the light source is a key factor in determining the color rendering index. The proportion and intensity of the various colors contained in the spectrum directly affects the color rendering index. The wider the spectral distribution, the higher the color rendering index, and the more realistic the color performance.