Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eyeand is responsible for the sense of sight.[ Visible light is usually defined as havingwavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−11 to 7.00 × 10−11 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750 terahertz (THz).
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