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Spectral solar irradiance on the surface of the Earth at sea level measured on the island of Tenerife/Spain under a cloudless sky at noon on June 4th, 2001 (approximately 82° sun elevation above horizon), with approximately 94 mW/cm² (approximately 937 W/m²) total irradiance, within this, approximately 31 mW/cm² in the range of infrared-A. Spectral irradiance of a water-filtered infrared-A radiator (Hydrosun^® radiator 750 with a 7 mm thick water layer in the cuvette and with an orange filter BTE31) at approximately 200 mW/cm² (2000 W/m²) total irradiance, of which approximately 145 mW/cm² is wIRA. Measurements with spectral steps and resolution of 1 nm.
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 colour filter used; the wIRA radiator does not emit ultraviolet radiation (UV).