A light-year is the distance light travels in a year.
Light year is often confused with length of time but it is actually the distance. The distance light travels in one year is called one light year.
we know that , speed of light = 3 x 10⁸ m/s
time of a year in seconds = 3.15 x 10⁷ s
distance traveled by light is given as
distance = speed of light x time in year in sec
distance = (3 x 10⁸) x (3.15 x 10⁷)
distance = 9.5 x 10¹⁵ m