Sun Simulators

Source: EUS

Life on earth has adapted to its natural light habitat very efficiently. Artificial illumination for realistic and reproducible experiments with organisms, especially with plants, therefore requires careful design and shaping of the spectral irradiance. Not only the quantity, i.e. the irradiation intensity, but also the spectral quality must match seasonal and diurnal variations of natural global radiation as close as possible. This includes the steep UV-absorption characteristics resulting from the filtering of solar radiation by stratospheric ozone. Another critical point is the realistic balance of UV-B (280-315 nm), UV-A (315-400 nm), and PAR (photosynthetic active radiation, 400-700 nm).

No single artificial light source can simulate both spectral quality and spectral quantity of global irradiance. The globally unique irradiation system of EUS therefore combines metal halide lamps, quartz halogen lamps, and blue fluorescent tubes for the simulation of global irradiation from the UV-A range to the infrared wavelengths. Excess infrared radiation is removed by a water layer above the plant growth chamber. The UV-B portion of the solar spectra is supplemented by UV-B fluorescent tubes. The radiation output of these fluorescent tubes, however, extends to wavelengths below 280 nm. Selected borosilicate and lime glass filters in our system provide a sufficiently steep cut-off at the desired wavelength. Different combinations of filter glasses allow a variation of the cut-off wavelength, enabling us to simulate various UV-B scenarios. The diurnal variations of the radiation are realised by switching appropriate groups on and off.

The lighting data of the solar simulators and the phytotron chambers clearly prove that we are able to simulate the realistic shape of the UV-B edge and the UV-B:UV-A:PAR ratio very close to natural conditions. The figure shows the spectral irradiance in the small sun simulator compared to an outdoor spectrum measured at our site. The ratio UV-B:UV-A:PAR of the sun is 1:38:293 and of our sun simulator 1:36:281.

Selected Publications

Rai et al. (2019): How do cryptochromes and UVR8 interact in natural and simulated sunlight? Journal of Experimental Botany doi:10.1093/jxb/erz236.

Albert et al. (2006) Solar simulators as a tool for assessing the impact of UV radiation on organisms and ecosystems. UV News 8: 17-19.

Thiel et al. (1996) A phytotron for plant stress research: how far can artificial lighting compare to natural sunlight? J. Plant Physiol. 148: 456-463.