A plant growth cabinet providing a flexible facility for photomorphogenic and photoperiodic research is described. The growth chamber is divided into quarters which are optically isolated, and has a recirculating air-conditioning system. The various light sources and filters available are discussed in relation to their desirable features. The chosen sources of white light (metal halide discharge lamps) are capable of generating approximately 800 μmol m−2 s−1 (400 to 700 nm). Tungsten-halogen filament lamps are used to provide longer wavelengths. Infra-red filters (acrylic sheet and water) reduced heat loading to a negligible level. Data are presented for internode length in plants of Chenopodium album L. grown under different fluence rates of supplementary far-red light in the new cabinet.