A dielectric mirror including a glass substrate supporting a coating, the coating comprising moving away from the glass substrate: a first transparent dielectric high refractive index layer comprising niobium oxide and/or titanium oxide, the first transparent dielectric high refractive index layer having a thickness of from about 70-140 nm; a second transparent dielectric low refractive index layer comprising silicon oxide, the second transparent dielectric low refractive index layer having a thickness of from about 30-140 nm; a third transparent dielectric high refractive index layer comprising niobium oxide and/or titanium oxide; a fourth transparent dielectric low refractive index layer comprising silicon oxide; a fifth transparent dielectric high refractive index layer comprising niobium oxide and/or titanium oxide; wherein the first transparent dielectric high index layer comprising niobium oxide and/or titanium oxide is at least 10 nm thicker than one or both of (a) the third transparent dielectric high refractive index layer comprising niobium oxide and/or titanium oxide, and/or (b) the fifth transparent dielectric high index layer comprising niobium oxide and/or titanium oxide; wherein the coating does not contain any metallic reflective layer based on Al or Ag; and wherein the dielectric mirror has (i) a film side visible reflectance or a glass side visible reflectance of from about 50-90%, and (ii) a visible transmission of from about 10-40%, characterised in that the glass side visible reflectance of the mirror is at least about 30% higher or at least about 30% lower than is the film side visible reflectance of the mirror, and in that the mirror further comprises a symmetry adjusting layer located between the third transparent dielectric high refractive index layer and the fifth transparent dielectric high refractive index layer, wherein the symmetry adjusting layer comprises NiCr. a first transparent dielectric high refractive index layer comprising niobium oxide and/or titanium oxide, the first transparent dielectric high refractive index layer having a thickness of from about 70-140 nm; a second transparent dielectric low refractive index layer comprising silicon oxide, the second transparent dielectric low refractive index layer having a thickness of from about 30-140 nm; a third transparent dielectric high refractive index layer comprising niobium oxide and/or titanium oxide; a fourth transparent dielectric low refractive index layer comprising silicon oxide; a fifth transparent dielectric high refractive index layer comprising niobium oxide and/or titanium oxide; wherein the first transparent dielectric high index layer comprising niobium oxide and/or titanium oxide is at least 10 nm thicker than one or both of (a) the third transparent dielectric high refractive index layer comprising niobium oxide and/or titanium oxide, and/or (b) the fifth transparent dielectric high index layer comprising niobium oxide and/or titanium oxide; wherein the coating does not contain any metallic reflective layer based on Al or Ag; and wherein the dielectric mirror has (i) a film side visible reflectance or a glass side visible reflectance of from about 50-90%, and (ii) a visible transmission of from about 10-40%, characterised in that the glass side visible reflectance of the mirror is at least about 30% higher or at least about 30% lower than is the film side visible reflectance of the mirror, and in that the mirror further comprises a symmetry adjusting layer located between the third transparent dielectric high refractive index layer and the fifth transparent dielectric high refractive index layer, wherein the symmetry adjusting layer comprises NiCr.