Metamerism occurs when two colour samples appear equal under one viewing illuminant, but look different with another light. Note the substrates must also be assessed by CIE-illuminant A (incandescent lighting). In the illustrated example, both bodies have different spectrum, that may appear different depending on the illumination type and light source.
For standardised colour control it is necessary to choose D50 lighting for prints and D65 for industrial products, e.g. coatings, plastics, varnish etc. If detecting metamerism of the colours or substrates is required, additional illuminants/light sources are needed.
With TILO colour viewing booths you can choose between different dimensions and numbers of illuminants but they should always include at least illuminant D65 and A for detection of metamerism.