The Colour Rendering Index (CRI) is a measure of how effectively a light source exposes colours. It’s a scale used to measure the accuracy of colours under an artificial light source as compared to sunlight. Understanding CRI is important for making optimal lighting decisions for healthcare, residential, and commercial spaces.
What Is the Color Rendering Index (CRI)?
The Color Rendering Index (CRI) measures how well a light source can display the actual colors of objects compared to natural daylight. CRI, created by the International Commission on Illumination (CIE), is scaled from 0 to 100. The greater the CRI value, the better a light source can depict the colors of the objects it is lighting.
- CRI 100 is the reference ideal light from the sun.
- CRI 0 is when colours are totally distorted or just not perceivable.
A light source with a higher CRI will show the true colours of a room’s furnishings or objects under illumination, while a lower CRI light might make colours appear washed out, distorted, or unnatural.
How is CRI Measured?
First, here is a quick refresher on how colour perception works. Natural light, such as sunlight, is a combination of all the colours of the visible spectrum. The color of sunlight itself is white, but the color of an object under the sun is determined by the colors that it reflects.
A red apple, for example, appears red because it absorbs all colours of the spectrum except for red, which it reflects. When we use an artificial light source such as an LED lamp, we are attempting to “reproduce” the colours of natural daylight such that objects appear the same as they do under natural daylight. Sometimes, the reproduced color will appear quite similar, other times quite different. It is this similarity that CRI measures.
As you can see in our example above, our artificial light source (an LED lamp with 5000K CCT) does not reproduce the same redness in a red apple as natural daylight (also 5000K CCT). But do note that the LED lamp and natural daylight have the same 5000K colour. This means that the color of light is the same, but the objects still appear different. How could this be?
If you take a look at our graphic above, you will see that our LED lamp has a different spectral composition compared to natural daylight, even though it is the same 5000K white colour. In particular, our LED lamp is lacking in red. When this light bounces off the red apple, there is no red light to reflect. As a result, the red apple no longer has the same vibrant red appearance that it had under natural daylight.
CRI is calculated by comparing the color of several standardized color chips under an existing light source with the color of the same color chips under natural light (which is assigned a CRI of 100). The colors are selected so that they have a broad gamut of colors, and the amount of color shift is quantified. CRI attempts to provide a scale for comparison of a light source colour quality vis-à-vis daylight.
Importance Of CRI
1.Colour Perception Accuracy
High Colour Rendering Index (CRI) lighting – typically defined as CRI>90 – is crucial in fields where colour accuracy is important, such as photography, art, makeup, retail, and healthcare. It ensures accurate colour representation, aiding in tasks like skin tone matching, photo editing, and medical diagnoses.
2. Ambience And Comfort
High CRI light makes a room appear warmer and more inviting, while low CRI light can make it appear flat and cold. For residential purposes, we propose choosing lights with CRI>80. The higher the value, the better albeit at a higher purchase cost.
3. Safety And Visibility
In environments like hospitals, schools, or warehouses, high color rendering may be necessary for safety and productivity. For instance, in hospitals, high CRI lighting allows doctors and nurses to see the distinction between various tissue colours or medications. In factories or industrial environments, high colour rendering can assist workers in spotting defects or dangerous situations.
Which CRI Value Should You Choose?
Though CRI is a significant consideration, the preferred CRI rating varies with the use of the lighting:
| CRI | Recommendations |
| 100 | Suitable for places where colour rendition is significant, for example, art studios, museums, and hospitals. |
| 90-99 | Very good light sources for most residential and commercial areas, with good color rendering for general applications. Suitable for kitchens, living areas, or store environments. |
| 80–89 | Appropriate for less demanding uses, e.g., street lights or hallways. Color rendering may not be as precise, but still aesthetically attractive. |
| <80 | Typically applied to lower or less expensive lighting fixtures. Colors tend to get washed out or distorted, and these lights are generally not so desired for applications where visual clarity is important. |
CRI In Relation To Other Light Metrics
Although CRI is a crucial lighting factor, it isn’t the sole measurement that needs to be considered. Several others that also possess the potential to influence the light’s quality in a room include:
- Colour temperature: measured in Kelvin, describes how warm or cool a light is. Warm light (2700K) is welcoming and typically used in residential settings, while cool light (5000K) is stimulating and resembles daylight and is used in commercial spaces.
- Unified Glare Rating: UGR is a key factor in lighting design that quantifies glare in a space. It’s one of the factors used by lighting designers and manufacturers.
- Lumens: measures the total light output. This is typically referred to as brightness of the light and is typically directly proportional to the wattage of the lamp. Different spaces have different Lumen requirements. Residential have lower illuminations for comfort while factories and healthcare have higher illumination requirements.
- Luminous efficacy: measures how efficiently a light source converts electricity into visible light. Higher efficacy means less energy consumption for the same brightness. This is typically measured in lumens per watt. Modern LED light fixtures output from ~70lm/w to ~ 150lm/w. A fixture of 150lm/w will use half the power of the 70lm/w to produce the same perceived brightness.
For more information on CRI, please refer to the CRI wikipedia page.
Stay tuned to our blog to learn more about lighting as we cover the basic light metrics. Our LED lights and LED Strips are manufactured using high quality chips from Bridgelux, Osram and Cree with a minimum CRI of 80. Contact us for more information.
