Here, T = Coefficient of transparency
d = distance traveled by light in object
t = coefficient of property of material.
Refraction is actually the change of the direction of light passing from one media to another. The direction is changed because the speed of light is different in different media.
If we assume that, transparency coefficient is constant, Refraction is zero, and no light source can be seen directly through object, then,
For sharper images we consider, angular behavior of reflection, transmission at surface, and attenuation due to thickness: