1. Energy in the visible and near-visible portion of the electromagnetic spectrum (0. 4–1. 0 μm in wavelength). 2. In meteorology, a term used loosely to distinguish radiation in the visible and near-visible portions of the electromagnetic spectrum (roughly 0. 4–4. 0 μm in wavelength), usually of solar origin, from that at longer wavelengths (longwave radiation), usually of terrestrial origin.