A NEW SUNLIGHT SIMULATOR FOR ECOLOGICAL RESEARCH ON PLANTS

A new sunlight simulator was designed and built which meets the spectral and energetic requirements of experimental ecological plant research. Its radiation is generated by a combination of four commercially available lamp types: metal halide, quartz-halogen, blue and UVB fluorescent lamps. IR radiation is filtered by a layer (20 mm) of circulating water. The plant-damaging, short-wave UV radiation is eliminated by 13 mm of borosilicate glass. The total input power of the system is 40 kW. The net illuminated space for plants is 1.2 m x 1.2 m x 0.25 m (length x width x height). The geometric arrangement of 184 lamps, located in specially designed aluminium reflectors, and the high reflection coefficient of the aluminium walls result in diffuse incident light. Irradiances reach more than 1000 W m-2, but less than 10(-7) W m-2 below 280 nm; the measured illuminance is 102 klx; the photosynthetically active radiation (PAR, 400-700 nm) is 2200 mumol m-2 s-1. The spatial homogeneity and the temporal variation of the irradiance are satisfactory. The spectral distribution is much more similar to natural global radiation than any other simulator known. By using highly efficient and commercially available lamp types, the running costs remain low. Hence, for the first time, a simulator in the square metre range has been developed, which provides the irradiance and the temporal, spatial and spectral distribution of global radiation at an economically reasonable scale.