Clear objects are visible because they bend the light as it passes. There are four basic things that can happen to light when hitting an object:
Clear Thinking: Think of a spoon or a metal spoon. Light emanates from the surface of an object like a billiard ball, allowing the first image to appear on the object.
Horrible Thinking: Think of green wood, flowers, or brightly colored areas. Light radiates from the surface of the object in all directions, revealing the shape and color of the object.
Breastfeeding: Think of a black piece of charcoal or ashes. Light penetrates an object where it is absorbed and converted into heat.
Transfer / Reverse: Consider a glass of water. The lamp goes straight to an object, but its path bends as it enters and leaves the object.