Aluminium reflector having a reflection increasing coating

A reflector has a reflection enhancing surface layer system comprising a sandwich construction of an Al layer facing the reflector body, an outer layer (HI layer) of refractive index n2 and a sandwiched aluminium oxide layer (LI layer) of refractive index n1 lower than n2. The novelty is that (a) the LI layer is a transparent and pore-free barrier layer which is produced by anodising the Al layer and which has a dielectric constant ( epsilon 1, at 20 degrees C) of 6-10.5; and (b) the optical layer thickness (dopt,1) of the LI layer and that (dopt,2) of the HI layer satisfy the relationship dopt,i = di*ni = li* lambda divided by 4 plus or minus 10 nm. (i = 1,2), where di is the LI layer thickness (in nm.), d2 is the HI layer thickness (in nm.), lambda is the mean wavelength (in nm.) of the light incident on the reflector surface and l1 and l2 are odd natural numbers. Pref. the HI layer consists of an oxide of an alkali, alkaline earth or transition metal, a lanthanide or their alloys, esp. Ti oxide, PrTi oxide, LaTi oxide, Ta oxide, Hf oxide, Nb oxide, Zn oxide or Ce oxide. Also claimed is a process for prodn. of the above reflector.