The color rendering index, i.e. the CRI value, is always specified on a modern LED. It indicates how natural the colors of the illuminated object appear when illuminated. It is therefore also a criterion for the quality of the illuminant.
What is the color rendering index?
CRI stands for Color Rendering Index. This so-called color rendering index indicates how natural the color of an object or the environment appears when illuminated by a specific light source. The CRI is, so to speak, a comparative value that can be used to determine the color impression of an LED. The light quality of light sources can therefore be compared with the help of the index. Other common designations are reference index (R) or general reference index (Ra).
The value is always between 1 and 100 and has no natural unit. For comparison, natural sunlight, halogen, and incandescent lamps have a CRI value of 100. Fluorescent lamps, on the other hand, have a lower reference index of 60 to 90.
How is color rendering measured?
The color rendering of an LED can be measured using measuring instruments such as a spectrometer. The benchmark is always natural sunlight with a maximum value of 100. In order to determine the color rendering of a lamp, it is evaluated in terms of how close it is to the color rendering in natural light.
According to DIN 1619, 14 standardized reference colors are used for this – eight primary and six secondary colors:
- primary reference colors: mustard yellow, antique rose, light green, yellow-green, turquoise blue, aster violet, sky blue, and lilac violet
- secondary reference colors: yellow, green, saturated red, pink, blue, and leaf green
All colors are then checked with regard to their deviation of the color representation from sunlight by the respective LED. In this way, an objective assessment of the color rendering can be given.
LED color rendering index values explained
The CRI of a light source is given the designation Ra for the general reference index. While 100 means a completely natural color reproduction, the value 1 is assigned to unnatural lighting. All values from Ra 90 stand for very good reproduction. A value of Ra 80 and above is considered good color rendering. Anything below 80 should be avoided for your living spaces as your clothing or food may appear in a distorted light.
CRI values of different light sources in comparison
Different light sources each have different CRI values. Here you will find an overview of common light sources and a comparison of the respective color rendering index:
| bulbs | Color rendering index (CRI) |
| sodium lamp | 30–40 |
| mercury vapor lamp | 45–50 |
| fluorescent lamp | 60–90 |
| LED-Lampe | 60–90 |
| energy saving lamp | 80–89 |
| halogen lamp | 95–100 |
| light bulb | 95–100 |
| sunlight | 100 |
Although older LED lamps do not reproduce the natural colors quite perfectly in comparison to other light sources, modern light sources are constantly evolving and their color rendering index is improving. Today’s LEDs even achieve very good color rendering with a value of up to 90.
When is color rendering relevant?
The CRI of an LED plays an important role in your interior design. For example, high color fidelity is important in the following areas:
- Bedroom: choice of clothing
- Bathroom: mirror lighting
- Dining room: dining
If the colors are not reproduced naturally in private surroundings, this quickly leads to discomfort and dissatisfaction. High color fidelity of your LED lighting can remedy this. Luminaires with a Ra index of at least 80 are recommended for indoor use so that the colors shine to their full potential.
Good color rendering is also important in business – for example, in the case of security colors in the industry. There shouldn’t be any risk of confusion here. Furthermore, high color fidelity plays a role in spaces for graphic artists, doctors or architects, but also in supermarkets or in shops with retail space. For industrial applications and outdoor areas, a Ra index of at least 65 is sufficient.
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