The present invention relates to a process for dyeing keratin fibres, in particular human keratin fibres such as the hair, using one or more particular 2- or 4-azopyridinium dyes and one or more fluorescent dyes. The present invention also relates to a cosmetic composition comprising the dyes defined above, and also to a multi-compartment device containing said dyes. The present invention also relates to the use of said dyes for dyeing light keratin fibres, especially human keratin fibres such as the hair, in chestnut-brown, dark chestnut-brown, brown, brown with a glint, or even black, without using an additional dye other than those defined above.