Things to know about CRI
If you’ve been shopping for LEDs, you may have come across the term “CRI” or “Color Rendering Index”. Knowing what CRI is, and how important it is, will help you make a better, informed decision when buying LED Lights.
Here, we’ll go through everything about CRI, in layman’s terms, so going forward you know what it means and how important it is to you.
What Does Color Rendering Mean?
Let us begin by telling you about color rendering before we talk about the index. Color rendering denotes the ability of the eyes to differentiate between colors.
This ability is impacted by many factors, like the quality of the light. It also defines how well the shades of color objects appear differently when lit up.
When the color of any object is referred to, it usually denotes the color appearance of the light source (white-warm and white-cool) or the targeted object (white, brown, purple, pink, and red).
You may think that the color appearance of an object represents its actual morphological characteristic; however, it is nothing more than the way the object is perceived by our visual capabilities.
To put it better, color appearance is a calculated result of the observations done by three color channels of our visual system. Every channel processes the same luminance falling on the retina differently that leads the eye to see the colors differently.
What Does Color Rendering Index Mean?
Color Rendering Index or CRI was devised by the International Commission on Illumination a long time back. This is a scale that assesses the effectiveness of light sources in making the objects appear true or closer to true to their real color.
The index also compares the visibility of the colors of objects to the human eye when under any particular light source and then under natural light, i.e. under sunlight.
CRI is a universally accepted metric for color rendering capabilities and consists of point system between 1 and 100.
You should keep in mind that CRI has no relation with the color temperature of the light as the latter represents the tone of light. The color temperature of light only considers the true color emitted by the light source and not the colors emitted by any object when light shines upon it.
Most LEDs on the market today are offered in color temperatures ranging from 2700K to about 7000K.
You will find most homes are lit in either 2700K or 3000K
Offices, schools and outdoor lights are often in the 4000K range.
Warehouse, factories as well as outdoor lights, such as high power flood and stadium lights, are offered at 5000K.
It is quite obvious to understand that CRI indexing requires more than mere visual testing. There are many complexities in the process. CRI indexing involves complex calculations done with advanced machines that cannot be understandable to a layman.
The only thing you need to know is the CRI info and that is mentioned on the products by the manufacturers.
CRI uses color samples that are predefined and known as Ra which means rendering averages. The CRI scale has 15 colors in reality but only R1-R8 colors are used for the testing done in common practice mostly.
The first eight color samples used in CRI are all pastel and unsaturated colors. This is the main point that had received a lot of criticism from the experts.
The argument lies around the thinner spectrum of light that pastel colors exhibit. The result has been a shift towards the usage of all the 15 color samples or Re scale for measuring the CRI values.
The Rensselaer Polytechnic Institute says that the CRI test uses 8 different color samples. These color samples are put under different basic light sources and then their color temperature is compared with that of another referential light source. The difference in the color of the testing sample light and reference light gives the CRI value.
The value of CRI increases with the reduction in the value of the average difference of the two chromaticities. A 100 value CRI means that the tested light sample produced the same luminance as that of the reference which can be sunlight too.
From the chart below, it can be understood that 60 CRI doesn’t give higher visibility but the color differences are discernable.
How does CRI determine the efficiency of LED lighting?
After clearing out all doubts about the CRI, it’s time that we tell you how it impacts lighting systems. A National Lighting Product Information Program survey concluded on the huge importance that industry experts associate with CRI when it comes to selecting the right light for different facilities.
The survey included the average usefulness scores of 1.9 for the brand tag, 3.1 for bulb type, and 3.2 for CCT in comparison to the standard 3.5. All these scores are right! The CRI ratings cast a huge impact on the way lighting appears. You can clearly see the stark difference between the luminance levels of lights with different CRI ratings.
Higher CRI ratings of any light denote a better color rendition that makes the color, details, and texture of the object clearly discernible to the human eye. Such high CRI lights can make any object under them look so much better or even completely different.
Imagine the difference high CRI LEDs can make to different settings. For instance, the fruits and vegetables kept under high CRI lights in a grocery store will appear fresher and juicier than the rest.
Similarly, these lights play crucial roles in the hospital where accurate color rendering is absolutely essential for the surgeries, tests, and other activities that take place. On the other hand, low CRI lights make objects appear almost lifeless.
It is also important to understand here that the CRI of every light doesn’t have to be 100. This depends on the individual settings that have different lighting demands.
How to determine the ideal CRI?
Color perception demands differ according to the individual settings and accuracy is needed at some places.
For most general commercial and industrial applications, which represents 99% of the customers we sell to, 70-75 CRI is good enough.
It makes no sense to pay for higher CRI unless you have an operation where color accuracy is of the upmost importance. Car dealerships and retail box stores are commercial businesses where higher CRI would be desirable.
About the Author
Neil Peterson is Chief Operating Officer at LED Lighting Supply. He has been active in the LED industry for over 10 years and is responsible for product planning and management as well as revenue and operations at LED Lighting Supply. Much of Neil’s time is focused on customer engagement for large commercial and industrial lighting requirements. When not working, he enjoys family time, camping, fishing, and sports..