An optical element (1) for use in a luminaire, especially a linear luminaire, for creating a prescribed output light distribution pattern from light emitted by a light source at a predetermined location relative to the optical element (1), the optical element (1) comprising a body including a surface which comprises a faceted structure (3), the faceted structure (3) comprising one or more strips or rows (6) each comprising a plurality of primary facets (4), wherein, for any given strip or row (6) of primary facets (4): (i) each respective primary facet (4) within the given strip or row (6) is configured such that it redirects light from a respective input direction associated with that primary facet (4) into a respective output direction associated with that primary facet (4); (ii) each respective primary facet (4) within the given strip or row (6) is configured such that light propagating therefrom in a said respective output direction associated with that primary facet (4) contributes to the prescribed output light distribution pattern; and (iii) the respective primary facets (4) within the given strip or row (6) are configured such that: the distribution of the respective output directions associated with the respective primary facets (4) in the given strip or row (6) has a random or quasi-random character with respect to the positions of the respective primary facets (4) in the given strip or row (6), and the random or quasi-random character of the distribution of the respective output directions associated with the respective primary facets (4) in the given strip or row (6) is defined by a probability density function correlating with the prescribed output light distribution pattern and not with the positions of the respective primary facets (4) in the given strip or row (6).