An aquaculture luminaire (10, 12) generates below the water surface upward light (26) and downward light (24). The upward light (26) is all directed with an angle to the vertical greater than a threshold angle. The division of light between the upward and downward directions may be configurable. Alternatively or additionally, the threshold angle may be configurable so that it ensures the light exceeds the angle for total internal reflection at the water surface. In this way, the luminaire is adaptable to the intended installation position of the luminaire and/or the prevailing water surface conditions (e.g. waves).