[subzero1313]

Originally Posted by cohowap

http://en.wiktionary.org/wiki/light_year

light year (plural light years)

(astronomy) A unit of length (abbreviation ly) equal to the distance light travels in one year; used to measure extremely large distances.

(in plural light years; figurative, informal) A very long way.
The marathon runner in the lead is light years ahead of the one at the back.

(in plural light years; figurative, informal, nonstandard) A very long time.
Some of Leonardo da Vinci’s inventions were light years ahead of their time.

now now, post the rest of the page to be fair:

• The light year is a unit of length, but because it contains the word year is sometimes assumed to be a unit of time. Its use in the figurative sense of "a very long time" is nonstandard; it is preferable to use an alternative term in this case.