# How to measure light wavelength exactly?

1. ### silin

26
Hi people,

does anybody know what the simplest device that can be used to measure monochromatic light wavelength exactly? Thanks.

2. ### OlderDan

3,029
The simplest ways I can think of involve interference. For example, you can use:
A diffraction grating (probably the best)
A pair of optical flats with high precision spacers
An optical flat and a precision plano convex lens of known radius to form Newton's rings.