What does nm stand for in wavelength?

nm stands for nanometer.

In the context of light and optics, it is the standard unit of measurement used to express wavelength—the physical distance between consecutive peaks of a light wave.

Here are the key details:

• The Math: One nanometer is one-billionth of a meter (1 nm = 10^-9 m).
• The Visible Spectrum: The human eye can detect light with wavelengths ranging roughly from 400 nm (violet light) to 700 nm (red light). Wavelengths outside this range fall into categories like ultraviolet (shorter than 400 nm) or infrared (longer than 700 nm).

• Relevance in Optics: When specifying materials, coatings, or performance metrics for lenses, filters, and beam splitters, the operational wavelength is almost always given in nanometers. This is because the physical behavior of light—such as how it bends (refracts) or reflects—changes depending on its exact wavelength. For example, an anti-reflective coating might be optimized specifically to transmit a 532 nm green laser.