LED-based sun simulation

Source: EUS

Climate change has numerous and only rudimentarily understood impacts on plants in natural and agricultural ecosystems. The increase in CO2 emissions resulting from the use of fossil fuels is responsible for the anthropogenic greenhouse effect. Ground-level ozone formed by photochemical reactions of nitrogen oxides and hydrocarbons, nitrogen oxides themselves and other emissions such as particulate matter, are an increasing burden on humans, animals and plants.  Under global change the competitiveness of plants in the ecosystem as well as its stability can therefore change.

The spectral solar radiation used by plants not only serves as an energy source for photosynthesis, but also regulates various adaptation strategies to changing environmental conditions with a multitude of receptors. Indoors experiments must therefore take place under a radiation simulation which is as close to nature as possible (Döhring et al. 1996). In addition to the absolute level of irradiation, a realistic ratio of the spectral components from the UV (290-400) to the visible range (400-700 nm) to the NIR (700-1000 nm) is particularly important. Since these conditions depend on the position of the sun, the lighting system must take into account not only the daily course of irradiation, but also the changing spectrum over the season.

At present, the global radiation (sum of direct and diffuse solar irradiation) in the climate chambers at HMGU, from the ultraviolet (UV) to the near infrared (NIR) spectral range, is realized using conventional illumination technology and is based on metal halide lamps (Osram HQI 400 W), quartz halogen lamps (Osram Halostar 400 W), blue fluorescent tubes (Philips TLD 18/36 W) and UV-B fluorescent tubes (Philips TL 12/40 W) (Döring et al. 1996).

This project aims to develop a new, state-of-the-art, energy-efficient lighting system which can simulate the natural spectrum of the sun from UV to NIR in the visible spectral range using a wide range of LEDs (Light Emitting Diodes). The aim is to design a system which can simulate both the annual/daily variation of solar radiation as well as short-term fluctuations in irradiation and spectrum, e.g. caused by clouds. Changes in the spectral composition in photobiologically effective areas also allow targeted functional studies of photobiological processes against a natural radiation background. Additionally the new system should be able to produce an artificial light spectrum which already is being used in greenhouses for food production. This would also allow studies on the influence of certain wavelength on food-plants regarding the phenotype and metabolic composition.

References
Döhring T, Köfferlein, M, Thiel S & Seidlitz H (1996) Spectral shaping of artificial UV-B irradiation for vegetation stress research. Journal of Plant Physiology 148, 115-119.