What is the CRI or RA Value of My LED Lamp?

You often see it in the specifications of a light source: the Color Rendering Index (CRI) or colour rendering. This is often a number between 70 and 90, with the unit "Ra" following it. But what does this actually mean? And when is this value important?

What Does CRI Mean?

The colour rendering or CRI of a light source refers to how "true-to-color" the colours of objects appear under this light. For example, think of a red apple: in daylight, you see the true colour of the apple, but the colour looks very different when placed under a green light. The higher the CRI, the more accurate and natural the colours of objects will appear under that light source. You cannot determine the CRI just by looking at the colour of the light source itself, but by observing how the colours of objects appear under the lamp. This is because CRI is not so much about the colour of the light, but about how the colour of the light is made up. This is also known as the spectrum of the light.

How is CRI Determined?

The CRI can range from 0 to 100 and is determined by comparing a number of reference colours under the light source in question with the same colours under natural daylight. Then, for each colour, the deviation from the "true" colour is calculated. The more the colours under the light source match those under daylight, the better and higher the CRI. A CRI of 100 means that the lamp displays all colours exactly as they are in daylight.

What CRI Values are Acceptable?

For most indoor spaces, a CRI of 80 (Ra) is an acceptable guideline for colour rendering. However, it also depends on the function of the space; in a space where colour rendering is crucial for the activity taking place, a CRI of 90 is a better guideline. For example, in a museum, the colour of the light could change the appearance of a particular painting. With a low CRI, Vermeer's *The Milkmaid* suddenly looks very different! A high CRI is also recommended for spaces like paint shops or textile factories. Still unsure which CRI value is best for your space? Feel free to ask us for advice!