Why do clothes appear darker in color when wet? On the contrary water is colorless then how does this happen ?
Water increases the scattering angle of light on fabric, and as a result, light is reflected and refracted in a greater number of “directions” than it is from dry fabric. Your retina is therefore receiving less overall reflected light. Since our sense of sight is simply a sophisticated means of making sense of a wide array of complicated light signatures, your brain interprets this as being darker.
But wait.. If it’s scattering in all different directions, why would that make it appear darker? Imagine a dry tablecloth sitting on a table. Now pour water on it. No matter which angle you look at it from, it appears darker than when it’s dry. So the extra light must be absorbed somehow, not just scattered.
The material itself does not absorb more or less light when it is wet or dry, because at the microscopic level, the strands and fibers of the fabric remain separate from the water itself i.e, water is merely filling all the gaps between the fibers and is held in suspension by its own surface tension.
So, now that the fibers are surrounded on all sides (and in between) by thin layers of water, for light to reach the fibers of, say, a light blue shirt, it must pass through that layer of water before it strikes the fibers. There, nearly all of the light is absorbed except for the blue wavelengths, which are reflected. That blue light must again pass through the layer of water, wherein it is again refracted and scattered before leaving the surface altogether.
In the end, less light is reflected back to your eye. If you’re wondering, where that “missing light” is going, take a colored shirt, make a wet spot on it, and hold it up between you and a light source. The wet spot will appear noticeably brighter on the reverse side, because the light is being scattered within the water between all the fibers of the shirt, and more of it is leaving through the back side.
I’m no scientist, but I’d venture to guess that the amount of light energy coming through the wet spot on the reverse of the shirt is directly proportional to the amount “darker” the spot appears on the front side.
Source : Reddit.com
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