I remember reading this over 15 years ago, and feel it was old even then.
The story had a man sent to a planet for some reason (survey maybe?) and discovering that there are evolved life-forms on there, of a mechanical nature. They use solar energy to survive so effectively shut down overnight. There are night time predators that attack, and he shows them how to create batteries to fend them off.
During the story the robots talk about what is obviously infra-red and ultraviolet light, and one day he wakes up to find he can see in those spectra. He asks how they "fixed" his eyes, and gets shocked when one of the robots opens a drawer in it's body to show that they actually replaced them.
I seem to remember that the cover had a man in a spacesuit surrounded by huge crystals.