First, light travels at different speeds depending on what it is traveling through. For example, light travels faster through empty space then it does air. It also travels faster through air then in water.

Second, light refracts. This means when it goes through one substance (air) into another (water) at an angle, the ray of light changes direction.

Based on this, I would say that after it rains, light is being refracted through the water droplets on the ground sending it back into the air making the world look brighter.

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