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Figure 4: Comparison of the spectra of the sun at sea level and of a water-filtered infrared-A radiator

Spectral solar irradiance at sea level (with the sun at the zenith and for a mean Earth-sun separation) as in Fig. 1 (adapted from [97]) and spectral irradiance of a water-filtered infrared-A radiator (Hydrosun radiator 501 with 10 mm water cuvette and orange filter OG590) at approximately 210 mW/cm (= 2.1 x 10 W/m) total irradiance as in Fig. 3 (from [1]).

The spectrum of the sun at sea level includes ultraviolet radiation (UV, <400 nm), visible light (VIS, 380-780 nm), and infrared radiation (IR, >780 nm). The spectrum of the water-filtered infrared-A radiator includes only visible light (VIS) and infrared radiation (IR); the visible part depends on the used color filter; the wIRA radiator does not emit ultraviolet radiation (UV).

Both spectra show the decreased irradiance of the absorption bands of water.