# Why Geometrical Optics works for objects much larger than the light wavelength?

Anish Joshi
TL;DR Summary
Read that Ray Optics explains reflection, refraction, formation of shadows, as the wavelength of light is negligible compared to day-to-day objects. Want to understand why Exactly?
The reason Geometrical optics works in case of formation of shadows, reflection and rarefaction is that the wavelength of light is much smaller compared to the reflecting/refracting surfaces as well as shadow causing objects that we use in day-to-day life.

I understand how the wavelength is negligible compared to the size of the object. But I want to understand the mechnaism - why and how does the small wavelength matter here?

First question here, so I apologize if there are any mistakes!

Gold Member
OK, then you'll want to study "Diffraction" which describes how waves propagate through/past restrictions (like the diameter of a lens). You can also study "Huygens Principle". Also look for videos of diffraction of water waves in a wave tank. That's classically very similar to what light does.

Basically, shadows (or light beams) always have fuzzy edges. If the object is small enough all you get is fuzz. If you have a big object, no one cares about a relatively small amount of fuzziness at the edges.

Anish Joshi