Why do people prefer black-on-white on Kindle/ebook readers, but white-on-black in IDEs?

Why do people prefer black-text-on-white-background for their Kindle / ebook readers; but bright-text-on-dark-background for their IDEs?

Both are instances of reading text on a screen. Scientifically, one of them has to be more efficient (i mean faster and more accurate reading, not energy consumption) that the other. Do you know which one?