A unit of measurement used to specify wavelengths within the electromagnetic spectrum, particularly in light and spectroscopy. One angstrom (Å) equals one ten-billionth of a meter (0.0000000001 m). In photography and optics, visible light occurs approximately between 4000 Å and 7000 Å, corresponding to the range of colors the human eye can perceive. Understanding angstroms is important for color science, filter design, and controlling light-sensitive materials in film and digital imaging.