A PHYTOTRON FOR PLANT STRESS RESEARCH - HOW FAR CAN ARTIFICIAL LIGHTING COMPARE TO NATURAL SUNLIGHT

Plants have adapted very efficiently to their natural light habitat. A rtificial plant illumination, therefore, requires careful design. Not only the quantity of radiation per area or volume (intensity) bur: als o the spectral quality has to match seasonal and diurnal variations of natural global radiation as close as possible. The GSF Research Cente r has developed a phytotron system especially devoted to plant stress research, where these requirements are of particular importance. The p hytotron consists of seven closed chambers (4 walk-in size chambers, t wo medium and one small sun simulator). Our contribution outlines the basic design of the lighting and presents spectral data. A good approx imation of terrestrial global radiation is achieved if several commerc ially available lamp types are combined and adequate filters are appli ed to reject unwanted infrared and harmful ultraviolet radiation. A pr ogrammable switch control for the individual lamp banks allows a varia tion of both spectrum and intensity of the illumination. Spectroradiom etric measurements show that the maximum level of illumination in the small and in the medium size chambers can compete both in spectral dis tribution and in intensity with outdoor global radiation for solar ele vations up to 60 degrees. The maximum light level available inside the large walk-in chambers reaches an irradiance corresponding to solar e levation of 50 degrees. The UV-B:UV-A:PAR ratio, which mirrors the spe ctral balance of plant lighting, can be adjusted to values following t he diurnal variation of natural global radiation.