What is Color Rendering Index (CRI) for LED Lights? The Definitive Guide

1. What is CRI?

Definition

What is the meaning of CRI in LED lamp? CRI is the abbreviation of Color Rendering Index, which refers to Color Rendering Index. The concept of Color Rendering Index is introduced. The color rendering index is represented by Ra. The larger the Ra value is, the better the color rendering property of the light source is. Ra is the color rendering index (represented by Ra, the greater the Ra value, the better the color rendering of the light source).

Chroma refers to the reduction of objects by light. Good color rendering means that the color of the object in this light is closer to the color in the sky at noon. Should choose 3 base color water to besmear fluorescent powder lamp tube to be able to filter off more ultraviolet ray, its life is long, chroma is tall, rise than common fluorescent lamp brightness 30%, chroma is as high as 80.

For lighting practitioners, the CRI is a common term. You often see the CRI value on the data of the light source and know that it reflects the good or bad of the light source in terms of color rendering.

But what does it actually mean? The higher the CRI, the better, but do people know what it actually measures and how? For example, the OLIGHT S1MINI has a CRI value of 90. What does that tell us? The lighting quality of the museum must be above CRI 95 and why?

Simply put: color rendering is an important aspect to evaluate lighting quality, color rendering index is an important method to evaluate the color rendering of light source, is an important parameter to measure the color characteristics of artificial light source, the higher the color rendering index, the better the color rendering of light source, the stronger the color restoring ability of the object.

CRI color smaples

The international commission on illumination (CIE) defines color rendering as the effect of a light source on the color appearance of an object compared to a standard reference light source. In other words, CRI is a measurement method for color recognition of a light source in comparison with a standard light source (such as sunlight).

The CRI metric is not far off. It was originally developed to describe the chromosome of fluorescent, which have been in widespread use since the 1960s, and to help users understand the applications of spectroscopically linear fluorescent.

CRI measurements are closely related to the difference between the appearance of the specified 14 color samples (hereinafter referred to as “color samples”) under the measured light source and the appearance under the standard reference light source.

Although the derivation of CRI is mathematical and an actual color chart cannot be used to determine the value of CRI, these color samples are real and are selected from the mun sell color samples.

The first 8 color samples are usually used to measure the general color rendering index (the CRI value that people usually put forward refers to the general color rendering index). The selected TCS01~TCS08 have medium saturation and roughly the same brightness, and the color range covers the whole visible spectrum.

The last six are specially colored samples, rarely used from TCS09 to TCS14, which include more saturated primary colors in addition to imitating European skin tone and leaf green.

2. CRI Technique

CRI values

Although these color samples are carefully specified and real objects can produce the color of these color samples, it is important to understand that the CRI values are derived entirely by calculation without the need to illuminate the real color samples with a real light source.

What we need to do is to compare the spectrum of the measured light source with that of the color sample, and then deduce and calculate the value of CRI by mathematical analysis.

Therefore, the measurement of CRI values is quantitative and objective, and it is by no means a subjective measurement (the subjective measurement relies solely on a trained observer to determine which light source has the better chromogenic properties).

The comparison based on color perception is also significant provided that the color temperature of the measured light source and the reference light source must be the same.

For example, it would be a waste of time to try to compare the difference in appearance between a warm white light source with a color temperature of 2900K and a cold white light source (sunlight) with a color temperature of 5600K.

They must look different, so the first step is to calculate the relative color temperature (CCT) of the measured source from its spectrum. Once you have this color temperature, another reference light source of the same color temperature can be created mathematically.

CRI metric

For the measured light source which color temperature is lower than 5000K, the reference light source selects the black body (Planck) radiator, while for the measured light source whose color temperature is higher than 5000K, the reference light source selects the CIE standard illumination body 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 measured light source. The spectrum of the measured light source is combined with each color sample to get another set of color points. If the color points under the tested light source correspond to the color points under the reference light source exactly, we will consider that their color rendering properties are the same and locate their CRI value at 100. In the color map, the farther the color point under the measured light source is from the corresponding ideal position, the worse the color rendering performance and the lower the CRI value.

Calculate the color displacement of 8 pairs of color samples separately, then calculate 8 special color rendering indexes (the CRI value of light source for a certain color sample is called special color rendering index), and then take their arithmetic mean value, so the value obtained is the final CRI value. The CRI value of 100 indicates that there is no color difference between any pair of 8 pairs of color samples under the measured light source and the reference light source.

3. Why is CRI important in LED lighting?

Not all light is made equal; some light renders color better than others. Color Rendering Index (CRI) is the measurement of how colors look under a light source when compared with sunlight. The index is measured from 0-100, with a perfect 100 indicating that colors under the light source appear the same as they would under natural sunlight.

This rating is also a measurement in the lighting industry to help discern naturalness, hue discrimination, vividness, preference, color naming accuracy, and color harmony.

– Lights with a CRI that is measured greater than 80 are considered to be more than acceptable for most applications.
– Lights with a CRI that is measured greater than 90 is generally considered “High CRI” lights.

These lights have important applications especially for photography, retail display and grocery lighting, where accurate color presentation is key. High CRI lighting is equally valuable in home use, as it can transform a room by highlighting design details and creating a comfortable, natural overall feel.

Testing for CRI requires special machinery designed specifically for this purpose. During this test, the light spectrum of a lamp is analyzed onto eight different colors (or “R values”), termed R1 through R8 There are 15 measurements which can be seen below, but the CRI measurement only uses the first 8. The lamp receives a score from 0-100 for each color, based on how natural the color is rendered in comparison with how the color looks under a “perfect” or “reference” light source at the same color temperature as that lamp.