What is the total precentage of radiation that is reflected by earths atmosphere

Around 48 % of the incoming solar energy passes through the atmospheric layer of the earth. The water vapor,ozone and dust present in the atmosphere absorbs 23 percent of incoming solar energy .Thus about 71% of the incoming solar radiation is absorbed by the earth. The rest 29% of the incoming solar radiation is reflected back into the space.

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.