None. Even though the two terms sound as if they're two forms of the same thing, they're not. A "year" is a period of time. It's the time between two of the same person's birthdays, the time between...
This is not a proper question. A light year is not a period of time. It is the distance light travels through space in one year's time - about 5.86 trillion miles.
An Earth year is a measure of the time it takes for the earth to make one complete orbit of the sun. So this is actually a unit of time. A light year is the distance light will travel in one Earth...