What Is CRI? The Parameter That Reveals the True Colours of Objects
Short answer
CRI (colour rendering index) is a value from 0 to 100 that measures how accurately a light source shows colours compared with daylight. CRI 80 is sufficient for offices and homes; in shops, restaurants and galleries, CRI 90 or higher and an R9 value (which measures saturated red) of at least 50 are required.
Why does the dark red jacket you saw in a boutique look orange when you get home? Why do the strawberries that looked so tempting in the supermarket look pale at home? They all have a common cause: light that shows colours wrongly. And the parameter that measures this is called CRI.
What is CRI? The basic definition
CRI (colour rendering index) expresses numerically how accurately and realistically an artificial light source renders colours compared with a reference light source (daylight or full-spectrum light). The scale runs from 0 to 100. A value of 100 represents the perfect colour rendering of daylight.
By its standard definition, CRI is the average of measurements made on 8 to 15 test colours specified by the IES (Illuminating Engineering Society) and the CIE (Commission Internationale de l'Éclairage). These test colours are pastel and saturated tones representing the part of the spectrum to which the human eye is most sensitive.
The CRI scale: what the values mean
- CRI 90–100 — Excellent: Shows colours closest to daylight. Indispensable for art galleries, museums, operating theatres, textile workshops, luxury shops and professional photography studios. Values of Ra 95+ in this range are now referred to as "high fidelity".
- CRI 80–89 — Good: Sufficient for general-purpose indoor use. Offices, homes, schools and most commercial spaces work well in this range. EU and ENEC directives set a minimum of CRI 80 for many applications.
- CRI 70–79 — Moderate: Colour quality begins to fall noticeably. Acceptable for environments where colour sensitivity is unimportant, such as industrial warehouses and factory corridors.
- Below CRI 70 — Low: Colours look pale, wrong or artificial. Long-term exposure can cause problems for health and comfort. Using this value in quality products is no longer recommended.
How is CRI measured? The technical process
CRI is measured with a spectrometer. The instrument measures the wavelength distribution of the light source (spectral power distribution, SPD) and compares it with a reference light source. According to the CIE standard, the test colours consist of eight pastel colours, R1 to R8. Extended measurements also include additional test colours such as R9 (saturated red) to R15 (Asian skin tone).
The R9 value is a parameter that deserves particular attention. It is not included in the standard CRI calculation, but it tells you how accurately red colours (meat, wood, artworks) are shown. A product with CRI 90 does not necessarily have a high R9 value. In high-quality lighting products, an R9 value of at least 50, preferably 80 or above, is targeted.
The difference between CRI and colour temperature
These two parameters are often confused, but they measure completely different properties. Colour temperature (Kelvin) describes whether the light looks warm or cool. CRI tells you how accurately the light shows colours. One light source can be 2700K (warm) with CRI 95; another can be 6500K (cool) but CRI 70. Colour temperature sets the atmosphere; CRI sets the quality.
Which CRI for which space?
| Space | Recommended CRI | Note |
|---|---|---|
| Art gallery / museum | At least 95 | Preferably R9 ≥ 80 |
| Luxury shop / boutique | At least 90 | R9 ≥ 50 for textiles |
| Restaurant / hotel | 85–90 | R9 important for food presentation |
| Office / school | 80 | 85 or above recommended |
| Home | 80–90 | Sufficient for comfort |
| Industrial area | At least 70 | 80+ if colour discrimination is needed |
The hidden cost of low CRI
Products with low CRI look cheaper at first. But in practice they can create serious costs. Colour defects that go unnoticed in quality control under CRI 70 light in a textile factory lead to customer returns. A doctor examining patients under CRI 75 light in a hospital corridor may miss cyanosis (a bluish discolouration) of the skin. Lighting below CRI 80 in a shop makes customers perceive products in the wrong colour and increases return rates. In other words, investing in CRI is a quality decision that pays for itself in the long run.
Conclusion
CRI is one of the most critical quality indicators of a lighting product. As important as lumens (brightness) and watts (power), this parameter directly affects how people perceive colours, their psychological comfort and their purchasing decisions. When choosing lighting, always ask about the CRI and request the right range for your application.
Frequently Asked Questions
Is the difference between CRI 80 and CRI 90 visible?
In general office use the difference is limited. Where colours matter, such as skin tones, food, textiles and artworks, CRI 90+ light shows colours clearly more vivid and natural.
What is the R9 value and why should it be asked for separately?
R9 measures how accurately the saturated red test colour is shown and is not included in the standard CRI average. So two luminaires with CRI 90 can have very different R9 values; in projects where meat, wood and skin tones matter, "CRI > 90, R9 > 50" should be specified together.
Are CRI and colour temperature the same thing?
No. Colour temperature (Kelvin) describes whether light looks warm or cool; CRI describes how accurately it shows colours. A 2700K light can have CRI 95, and a 6500K light can have CRI 70.
How is CRI measured?
The spectral power distribution of the light source is measured with a spectrometer, and the appearance of test colours R1–R8 is compared with their appearance under a reference light. Extended measurements also include colours R9–R15.