Linked from
The 17 pages that link to Color rendering index, each with the reason it gives.
MetamerismRelated: Metameric white lights can score poorly because they match whites, not surfaces.
Luminous efficacyRelated: A source can have high efficacy yet render colors poorly.
Color matchingRelated: Its evaluation relies on comparing sample appearances under different lights.
Electric lightRelated: Electric lamps can differ sharply in how faithfully they show colors.