Colour rendering, which is expressed as a score between Ra 0 and 100 on the Colour Rendering Index (CRI), describes how a light source makes the colour of an object appear to human eyes and how well subtle variations in colour shades are revealed. The higher the CRI rating, the better the ability of a light source to accurately reproduce the colours of the object it illuminates.
UEFA’s requirements stipulate that for the artificial illumination system to produce good colour, the CRI rating needs to be greater than Ra 80 for UEFA elite level A, levels A and B, Ra 70 for level C, and Ra 65 for UEFA level D stadiums.
The CRI generally provides a good level of assessment of the chromaticity of large-scale lighting systems in stadiums. Designers and suppliers of football stadium illuminance systems must nevertheless be aware of the potential areas of concern in which the CRI may not sufficiently evaluate the colorimetric quality of a light source in a particular range of the spectrum. In video and film production, the colour spectrum of luminance produced by LED lighting in specific wavelength bands may not provide sufficient colour rendition.
The extended Re (also sometimes expressed as CRI) provides additional information for the whole colour spectrum of a light source and is measured during test and evaluation process. It should be noted that LED luminaires should be carefully evaluated, and it is generally recommended that the CRI R9 (wavelengths longer than 600 nm) values are assessed to be sufficient. The extended CRI is denoted by the symbol Re and along with the Television Lighting Consistency Index is recognised as providing a detailed and thorough analysis of a light source. However, the UEFA Lighting Guide 2023 continues to use the more basic version of Ra in order to provide consistent continuity of this assessment. This will also ensure existing stadiums that produce a Ra of the appropriate level are assessed to meet the requirements. As an example, it should be noted that for many LED light sources that are tested to provide a Ra value of 80, the same light source will produce a Re value in the region of Re 75–76.
The Television Lighting Consistency Index (TLCI) was developed as an alternative method to evaluate the chromaticity quality of a light source within the television environment. Rather than assess the performance of a luminaire directly, as the CRI does, the TLCI mimics a complete television camera and display, using only those specific features of cameras and displays which affect colour performance. The TLCI is recognised to be an effective method for evaluating the chromaticity quality of a light source and is recommended as good supplementary information when evaluating different light-source products.
CRI(e)/Re test colour samples (TCS)
Chromaticity values of lamp/LED
The following diagram provides an example for a chromaticity test and should be used as a guide to the level of information required for all new and old UEFA stadiums.
Note that only the extended Colour Rendering Index, CRI(e), is used for both test and evaluation purposes.
Chromacity values of lamp/LED after testing
