Here’s the basic idea: Pluto is 3.6 billion million miles away from the sun, which is about 40 times the distance of Earth to the sun. Obviously, the amount of light that reaches Pluto is far less than what reaches Earth. After traveling about five and a half hours, at the brightest point in Pluto’s day, the sun’s light is about 1/900th the intensity that it is on Earth.
But that doesn’t mean the planet is totally dark. While it may be a fraction of the brightness of an Earth day, it’s still 300 times brighter than the light from Earth’s moon. You’d probably have no trouble reading on Pluto at noon (unless, of course, you take your space helmet off).
The thing is, you don’t have to imagine what this amount of light is actually like, since you likely live it twice a day. Every day, just before sunrise, and just before sunset, the little light we receive from the sun is the same amount of light as a Pluto day at noon. NASA appropriately calls it “Pluto Time.”