Colour critical assessment in the graphic arts industry is performed by using D50 simulators that obey rigorous criteria stipulated in ISO 3664 for years. Here multichannel LED based viewing cabinets are increasingly used. However the impact of phosphor converted LED based lighting for general lighting applications in lieu with colour assessment in prepress and press environments can be critical. Incorrect lighting might destroy ISO 3664 conformance and lead to colour differences that are larger than the domain of application of the advanced colour tolerances equations. A user friendly collection of metameric pairs was designed to solicit actual visual differences under 10 typical LED-based luminaires and six ISO 3664 compliant cabinets. These findings were correlated with modern colour rendering metrics including the new CIE fidelity index. Finally colour rendering tolerances will be proposed for general lighting that is used to support colour critical viewing and to certify LED based luminaires.