Here's why:

* Distance: Neptune is the farthest planet from the Sun, about 30 times farther than Earth. This means it gets much less sunlight.

* Sun's Brightness: The Sun's light intensity decreases as you move away from it. At Neptune's distance, the Sun appears as a very bright star, but still provides only about 1/900th of the light Earth receives.

Therefore, Neptune experiences a very dim, twilight-like level of light.