eli5 Why it’s darker when wet ? Like water on concrete or fabrics.

Question

(Sorry for the title, english is not my first language)
When it’s raining, darker dots appears where raindrops falls.
Or a wet stain on your shirt appears darker, why ?

In: Chemistry

Answer 1

What you see when you look at a surface is the light (of the sun or any other source) reflected off the surface.

Water impacts this in two ways.

1. Water can absorb some light that the surface ordinarily would reflect, causing it to appear darker. (Cloth or paper that is wet)

2. Water may cause more pure reflection where ordinarily would diffuse, so instead of a generally light region, it will appear darker from most angles, but a blinding flash from the one reflected angle (wet road at night with headlights).