UV LED-based solar flare simulator for space environment studies

The study of solar and stellar UV radiation, including dynamic spectral variations, is of extreme importance in photobiology and material testing under space-grade irradiation conditions, particularly in potentially habitable exoplanets. This work describes the development and experimental validation of an adaptive multi-wavelength UV LED simulator. The simulator integrates 12 UV wavelengths grouped into 10 independently controlled channels. Each channel is managed using custom software, which, after an initial optical characterization, allows the user to select and reproduce the desired output spectrum. A novel driving architecture has been adopted to ensure maximum signal stability and to avoid high-frequency ripple typically introduced by switching regulators. A key feature of the system is its dual-stage optical mixing architecture: two sequential light-mixing chambers are separated by engineered diffusers, achieving excellent spectral irradiance homogenization. Preliminary tests showed irradiance variation of less than ±7% at each wavelength across an 80 mm diameter area. The inner surfaces of the chambers are coated with high-reflectivity silver-finish material to maximize photon recycling and spatial uniformity. This configuration eliminates spectral inhomogeneities and guarantees a uniform emission profile over the entire 150 mm output aperture. The impact of temperature has been evaluated and compensated by means of an active cooling system, providing thermal stability for both the LED array and the driving electronics during continuous operation. The radiation field expected at the surface of selected potentially habitable exoplanets were modeled and processed by the Trieste Astronomical Observatory (INAF), starting from stellar flare data and applying computational attenuation based on Archean anoxic atmospheric models. The resulting spectra were used as input to the system. Experimental results confirm that, after the initial thermal transient, temporal stability is very good (within 1%) and mainly influenced by ambient temperature fluctuations. In terms of intensity, the system can replicate typical young Sun and M stars flare events corresponding to a 3 Gyr-old Sun.