Here's why:

* Visible Light: The visible spectrum of light, the part we can see with our eyes, spans wavelengths from about 400 nm (violet) to 700 nm (red).

* Convenience: Nanometers are a convenient unit for expressing the very small wavelengths of light.

* Other Units: While nanometers are the most common, you might encounter other units like:

* Micrometers (µm): 1 µm = 1000 nm

* Angstroms (Å): 1 Å = 0.1 nm

Let me know if you have any other questions about light!