I am looking for any solution which can help me out to count the number of droplets or amount of water on a mirror or glass.
I am going to spray mist on two glass or two separate mirrors. and I am looking for solution so I can compare the amount of water deposited on each glass/mirror OR I can count the number of water droplets on each mirror/glass and can display it.
Can I use any light sensor for this. if yes How?
No, not ANY light sensor. You must determine a light wavelength that is absorbed by water, but not by glass.
Once you know that and can produce that particular light, then a sensitive sensor to that wavelength can sense the difference in the light transmission before spraying with water and after spraying with water.
Rest is up to you.
Paul
Veeeery difficult ... car automatic windscreen wipers make use of the effect the droplets have on light reflected off the back of the glass . Might be worth a google .
Might help to say what your project is trying to do ; there maybe an easier solution