While light ray pass a transparent material on wet/dry surface, there is some phenomenon happened.

[BrainOnLost]

Hello there, I found when light ray pass a transparent material on wet and dry surface, there is some phenomenon happened.

This is what seem on a dry surface.

https://i.imgur.com/ouPkmpP.png

The observation could seem the light was spread evenly on the surface.

This is what seem on a wet surface.

https://i.imgur.com/1Y95wAm.png

Something weird happened, the light was spread like a ring with a hollow on the center.

I guess this phenomenon was related to Frustrated Total Internal Reflection, but could somebody can explain briefly on this?