Here's why:

* Closest to the Sun: Mercury is the closest planet to the sun, orbiting at an average distance of 36 million miles (58 million kilometers).

* Inverse Square Law: The intensity of light decreases with the square of the distance from the source. This means that as you get further away from the sun, the amount of light you receive decreases significantly.

While Venus is closer to the sun than Earth, the thick clouds in Venus's atmosphere reflect most of the sunlight away from the planet's surface. This makes Mercury, despite being smaller and with a thinner atmosphere, receive the most light from the sun.