Is light a 3-dimensional wave?And how is that measured?

Question

I'm assuming the answer to the first question is yes, if I'm wrong, this will be an easy one to clean up. Forgive me is this is a stupid question. When thinking of light waves or particles as waves, I have always thought of them as the waves on the 2-D surface of the water. It just dawned on me how overly simplistic this view was when I was thinking of the light from distant stars reaching us. It's so neat and orderly to have that 2-D wave. When I think of 3-D waves, my mental image falls apart. How do we discern one light source from another? I feel like they should all combine together, making their origin unknowable. I obviously know this isn't the case because I am able to differentiate the wavelengths of light being reflected off the various objects in my everyday life. I just don't understand how the wavelengths of the light doesn't add up...

I really hope someone could clear this up for me. Maybe explaining how EM detectors differentiate wavelengths, or something? I don't know.

Answer 1

If you consider just one plane wave going on a particular direction through a lens, it's pretty easy to see that it is focused to a point. The point is on the line that goes in the same direction as the wave, some distance beyond the lens. A different plane wave approaching from a different direction gets focused to a different point the same distance beyond the lens.

So the energy from all the waves approaching from different directions is focused only to separate points whose positions correspond to the directions of approach.

In the case of our eyes, those points are all located at different positions on our retina, at the back of the eye.

Answer 2

Yes, it is a 3D wave. It is easily seen in the equation of motion of a probe charge in such a wave: the Lorentz force is a 3D force.