What Is Color Rendering Index?

For those engaged in the LED light industry, CRI is a commonly used term. You often see the CRI value in the data of the light source, but what is its actual meaning? The CRI value of a LED light source is 95. What information does this convey? Here we will take you to fully understand what CRI is.

Article Guide: 
1. What is CRI in LED lights?
2. What is the difference between CRI and Ra?
3. How to choose the right CRI when buying led strip lights?
4. What is the relationship between CRI and brightness?
5. Is higher CRI better? High CRI VS Low CRI
6. How to find CRI value?

1. What is CRI in LED lights?

CRI(color rendering index) is an important method to evaluate the color performance of LED light sources. It is to quantitatively evaluate the color rendering of the light source and is the degree of consistency between the object color under the measured light source and under the reference light source.

The LED light source with high color rendering can reproduce the object color better, and the color we see is closer to the natural primary color, that is, the color under the sunlight. The LED light source with low color rendering has poor color reproduction, and the color deviation we see is also large.

As the light source, the high CRI 95+ led strip lights emit a soft and comfortable LED light like the morning sun, reduce visual fatigue, make the vision field clearer, and the image is more three-dimensional. It brings users a better lighting experience.

Color rendering index value of specific lamps
· Incandescent lamp: Ra97
· Daylight fluorescent lamp: Ra80-94
· White fluorescent lamp: Ra75-85
· Warm white fluorescent lamp: Ra80-90
· Tungsten halogen lamp: Ra95-99
· High-voltage mercury lamp: Ra22-51
· High-voltage sodium lamp: Ra20-30
· Metal halide lamp: Ra60-65
· Sodium thallium indium lamp: Ra60-65
· Dysprosium lamp: Ra85 above

2. What is the difference between CRI and Ra?

The original purpose of the CRI metric standard was to use it to describe the color rendering of fluorescent lamps that began to be used extensively in the 1960s and to help users understand that fluorescent lamps with linear spectral distributions can be applied on which occasions.

CRI has 15 test colors which are also called standard color samples. Use R1-R15 to represent the color rendering index of the light source for these 15 colors.

Numbers 1-8 are 8 natural colors, selected from the Munsell color scale, including various representative colors, and they have medium chroma and lightness.

Numbers 9-15 are 7 test colors, including red, yellow, green, and blue with higher chroma, skin color of young European and American women, the skin color of young Chinese women, and leaf green. 

The special color rendering index (Ri) is the color rendering index of the light source for a selected test color sample.

The general color rendering index (Ra) is the average value of the special color rendering index of the 8 colors of the light source pair numbered 1-8. Usually, we use the general color rendering index to characterize the color rendering of the light source. The greater the Ra, the better the color rendering of the light source.

Different light sources have different special color rendering indexes for the same test color, and Ra is also different. And the same light source has different special color rendering indexes for different test colors.

3. How to choose the right CRI when buying led strip lights?

The color rendering index of sunlight is defined as 100, and the color rendering index of incandescent lamps is very close to sunlight, so it is regarded as an ideal reference light source. But there are many types of incandescent lamps in real life and their applications are different, so their Ra values are not completely consistent. However, due to its low light efficiency and insufficient energy saving and environmental protection, it has gradually withdrawn from the stage of history.

Nowadays, the color rendering of led light strips is gradually improving, and the CRI value can reach 95. Because of their energy-saving and environmental protection, led strips light are currently more popular light sources.

In order to correctly express the original color of the object, a light source with a high color rendering index must be used. The higher the Ra, the higher the faithfulness to the natural color of the object. The value is close to 100, and the color rendering is the best.

Different application places have different requirements for the faithful color rendering of the light source. If you do not know how to choose the CRI for your led lighting, you can take the CRI chart below into consideration.

CRIPerformanceSuitable Places
Ra 90-100Excellent color renderingPlaces that require precise color contrast—color matching, color inspection, art galleries, museums, supermarkets, shops, restaurants, etc.
Ra 80-89Good color renderingPlaces that require correct color judgment—factory for printing, painting, fiber, and precision operations. Residential, hotel, and restaurant.
Ra 60-79Normal color renderingPlaces requiring medium color rendering—factory for general operations such as electromechanical assembly, surface treatment, and control room. Office and study are also allowed.
Ra 40-59Poor color renderingPlaces with low requirements for color rendering and small color differences —heavy industry factories such as machining, heat treatment, casting, etc., and outdoor streets.
Ra 20-39Poor color renderingPlaces with no specific requirements for color rendering—warehouse and outdoor road.

Choose a specific color rendering index in special scenes such as meat product windows to clearly emphasize specific colors and express better colors. In this case, it is usually necessary to increase the corresponding special color rendering index according to the color of the illuminated object under the premise of ensuring that the Ra meets the requirements.

For example:

1. For the LED lighting source of meat products in supermarkets and shops, the R9 color rendering index is particularly important. Meat is usually reddish. So a high R9 can make the meat look fresher and more delicious.

2. For studios and other occasions where the skin color needs to be truly reproduced, the R15 index of the lighting source must not be low.

4. What is the relationship between CRI and brightness?

We should pay attention to a problem, that is the higher the CRI, the lower the brightness. At present, the universal CRI with the highest brightness and good quality is 85, which is also the most circulating in the market.

If you want 90 high CRI led strip lighting and have a bright brightness at the same time, we recommend you to choose constant current led strip lights. Constant current led strips is no voltage drop. And it can achieve an ultra-long distance run and ensure that the LED color and brightness of the strip light keep the same. 

5. Is higher CRI better? High CRI VS Low CRI

If it is exposed to a light source with a poor color rendering for a long time, the sensitivity of the cone cells of the human eye will also decrease, and the brain will tend to concentrate more intentionally or unintentionally when distinguishing things, which can easily cause eye fatigue and even cause myopia.

And a low CRI will cause color distortion. From the perspective of protecting eyesight, the CRI of the led strip light used needs to be greater than 80.

Different scenes have different requirements for the CRI of the light source. Choose the appropriate CRI value according to your usage scenario.

6. How to find CRI value?

Although the color samples are carefully specified, and real objects can produce the colors of these color samples, the CRI value is completely derived from calculations. It is very important to understand that it is not necessary to illuminate the real color samples with real light sources.

What we have to do is to compare the measured light source spectrum with the spectrum of the formulated color sample, and then calculate the CRI value through mathematical analysis. Therefore, the measurement of CRI value is quantitative and objective. It is by no means just relying on a trained observer to judge which light source has better color rendering.

When you browse led strip products, CRI will be generally indicated in the product specifications. Pay attention to it if you want to choose a great CRI.