94.6%

The above photo shows the Earth, Moon, Venus, and Mercury. As planetary pie aficionados know, these bodies together comprise 94.6% of the inner solar system. Only Mars and the asteroids are missing. Looking at the full size image (click it) will show that the mare are clearly visible in the Earth glow.

On the Moon, the Earth is almost full in the sky, and it has 16 times the area and 3 times the surface brightness as the full moon does. So the Earthlight lights up the dark side enough for us to be able to see the lunar landscape.