An illumination system comprising a radiation source and a luminescent material comprising at least one phosphor capable of absorbing a part of the light emitted by the radiation source and emitting light of a wavelength different from that of the absorbed light, wherein said at least one phosphor is an amber to red-emitting cerium(III)-activated oxonitrido aluminate silicate of the general formula RE3-xAl2Al3-y—SiyO12-yNy:Cex, wherein RE is a rare earth metal, selected from the group of yttrium, gadolinium, lutetium, terbium, scandium and lanthanum, and 0.002≦x≦0.2 and 0