An optical module (30) for a LED assembly (1) is disclosed. The optical module comprises a plurality of optical elements (31) and a plurality of mounting structures (40), each mounting structure comprising a stepped arrangement of mounting elements, in which each mounting element defines a step of the stepped arrangement, each step defining a different mounting height for the optical module. Also disclosed are a LED assembly including such an optical module, a luminaire including such a LED assembly and a method of assembling such a LED assembly.