Question

How can we measure the wavelength of light?

Answer 1

I would use Young's Double Slit Experiment (1801).

Explanation:

This is one of the classical experiments in Optics and I think it was used by Young to evaluate the wavelength `lambda` of Sun light.
Here it is a diagram of the set up:

on the screen you will detect a series of bright and dark frinjes whose positions, `y`, can help you to evaluate the wavelength (`m` is the order, zero for the central maximum and `1, 2, 3,...` for the other maxima above or below the central maximum).