Consider the metal coin in figure. The right half is polished, while left half is unpolished. 

In a dark room, this coin is placed face up on the floor and illuminated with a thin-beamed flashlight, as shown in figure. A and B look at the coin from the position as indicated in figure

According to A, which half of the coin (if either) is brighter?

The polished half

The light reflects of the coin and reaches A’s eye.

As the polished half is smoother than the unpolished half, hence the polished half behaves more like a mirror. So, most of the light striking the polished half of the coin reflects instead of going diffusion reflection. Hence, A sees a high percentage of the light that hits the polished part of the coin.

Light hitting the unpolished half undergoes more diffuse reflection, bouncing off the coin in all different directions. Hence, a smaller percentage of that light reaches A’s eyes. So, for A the polished half looks more brighter than the unpolished half.