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CRI: the importance of accurate colour reproduction

The Colour Rendering Index​ (or CRI) measures the ability of a light fixture to accurately reproduce the colours of the object it illuminates​.  

The International Commission on Illumination (CIE) defines colour rendering as the “effect of an illuminant on the colour appearance of objects by conscious or subconscious comparison with their colour appearance under a reference illuminant.” 

A concept that many are already familiar with: objects appearing a different colour under a red or blue light. But how can this affect the performance of the LED lights in your growing environment? 


What is the Colour Rendering Index?

CRI is expressed on a scale of -50 to 100, with 100 representing how the colours are seen under a perfect light (such as the sunlight). 

A CRI below 70-80 is considered poor for commercial lighting​ application. When it comes to horticultural lighting, a CRI below 70 makes it harder to identify colours. This leads to many challenges, such as identifying leaves discolouration. 

Environments where rendering is critical will use LED chips with a CRI over 90. They are the preferred lighting solution for hospitals, textiles, printing/paint shops, art restoration, and food counters. 

CRI 70 80 90

CRI of different horticultural lighting 

Purple lights, made from a mix of red and blue lights, have a CRI ranging from -40 to 0​. Such a low CRI means it is practically impossible to identify any colour underneath it​ or details such as discolouration and insects. It is also extremely unpleasant to work under this kind of light​ in any type of growing environment. 

Traditional HPS lights often have a CRI between 25 and 40​, meaning they render colours in a way that is noticeably unnatural to the human eye. Although they are then performing a bit better than purple lights, they still make it difficult to identity colours and discolouration.  

Kroptek’s KP04 & KP08 light spectrums have been measured at a CRI higher than 90. This makes them particularly performant, creating a pleasant work environment for growers; on top of giving them the ability to realistically see colours and any other details like discolouration and insects.  


At Kroptek, we believe colour accuracy is incredibly important for growers to be able to grow the best quality plants. Therefore, our LED grow lights offer the best possible CRI and performance. To find out more about our LED solutions, click here.