The text plays on the stereotype of Vulcans from 'Star Trek' being extremely precise and logical, to the point of specifying an unnecessary level of precision for a simple task like replacing a light bulb. The humor arises from the juxtaposition of the precision in the number '1.000' with the mundane task of changing a light bulb, which typically would not require such precision.
Number of Vulcans needed to replace a bulb ? Precisely 1 . 000