Have you ever noticed that certain colours look very different under sunlight than they do under a street light? This is because the wavelengths emitted by different light sources cause our eyes to perceive colours differently. How a colour is seen under a light source is called colour rendering. Colour rendering is rated using the Colour Rendering Index, or CRI. We test for colour rendering by comparing the same colour under different light sources.

What is CRI?

The Colour Rendering Index (CRI) is a scale of 0 to 100 that measures the ability of a light source to accurately reproduce the colors of the object it illuminates:

• An index score of 100 indicates that the light is showing colours as they would appear in natural daylight.
• Above 90 is exceptional, displaying colours as accurately or nearly as accurately as daylight. LED lighting is now able to render colours more accurately than ever before, with some lamps reaching CRI scores in the high 90s.
• Between 80 and 90 is a good range that renders colours quite accurately. Many LED light sources have a high CRI of eighty or above.
• As the index drops lower than 79, light renders colours less and less accurately to the human eye. Below 50 is likely to be noticeably inaccurate.

Sunlight has a CRI of 100. Colours look good under sunlight. Greens look green, reds look red, and so on. High or low pressure sodium lights typically have a low CRI. You will notice colours seem distorted under old street lighting or parking lot lights. This is because high pressure sodium is usually used in these instances.

Where is CRI Important or Useful?

Depending on your line of business you are likely to want certain levels of CRI.

Colour rendering is crucial anywhere that food is involved, for example. Supermarkets, grocers, and butchers should consider lighting with higher levels of CRI. Good colour rendering makes fruit and vegetables look vibrant and ripe. After all, no one wants to buy a brown apple.

Fashion retailers usually want clothing and outfits to look as close in colour to what they would in natural daylight or even make colours stand out against each other and therefore high CRI levels are required.

Other types of applications where 90 CRI (Ra) might be needed for professional reasons include hospitals, textile factories, printing facilities or paint shops. And areas where improved aesthetics could be important, such as high end hotels and residences, will also benefit.

Though any score below 80 is technically considered “poor”, for an average household lamp or standard office, a CRI between 89 – 70 is perfectly fine. You might even want to go lower down to the 60s to achieve the ambience you are looking for, depending on the purpose of the room.