Daz1712:
If you have to work with light then you need to look at Lidar as an LDR will not do this, it is for light intensity ONLY.EG. You have two stars in the sky, one is bright and one is dim, conclusion! The bright star must be closer. Wrong.
Turns out the bright star is twice the distance of the dim one but is 4 times as bright.
Your answer was based on intensity only which is 2 dimentional thinking when we live in a 3 dimentional world.Daz
Nitpicking, but the stars would be equally bright in your numerical example.