The nanometer (nm) is a unit of length in the International System of Units, defined as 10−9 meter using the SI prefix system. The most common use of the nanometer is in measuring the wavelength of visible or ultraviolet light. Traditionally, the unit that had been used was the Ångstrom unit, equal to 0.1 nm = 10−10 m, but in the SI it is favored to use exponents of 10 which are multiples of 3, so in the SI the most convenient unit is the nanometer.