Why does condensation on a glass window make it opaque?

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SUMMARY

Condensation on a glass window creates an opaque appearance due to the presence of numerous tiny water droplets, which disrupt the passage of light. The light interacts differently at the water-glass and water-air interfaces, causing scattering. When a second piece of glass is pressed against the first, forming a uniform thin sheet of water, transparency is restored. This phenomenon highlights the importance of droplet size and distribution in light transmission.

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  • Understanding of light refraction and scattering
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dipole
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Fog condensed on a glass window is just a very thin layer of water droplets, so why is it so opaque to light? Normally light passes through a water-glass interface just fine, but why not in the case of condensation?
 
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dipole said:
Fog condensed on a glass window is just a very thin layer of water droplets, so why is it so opaque to light? Normally light passes through a water-glass interface just fine, but why not in the case of condensation?

It's not just the water-glass interface that's the problem, it's the water-air interface. You have lots of tiny beads of water on the glass, so incoming light will strike perpendicular to the surface of the water at one point (near the center of a droplet) yet almost parallel to it at another very close point (the edge of the droplet).

Take a second piece of glass, press it flat against the first so that water in between is pressed down into auniform thin sheet between the two surfaces, and it will go back to transparent again.
 

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