In many applications, high density polyethylene (HDPE) geosynthetics are exposed to sun-light throughout their service life. In this study, the depletion of antioxidants in HDPE with 2.7% carbon black subjected to sunlight exposure was evaluated. The sunlight radiation was simulated using a labora-tory xenon light weatherometer at three irradiation levels. Oxidative induction time (OIT) test was used to assess the depletion of antioxidant along the thickness of the test coupons to establish the antioxidant de-pletion profile throughout the exposure duration. The greatest decrease in OIT was obtained in the surface layer facing the sunlight irradiation, followed by the backside layer which was exposed to indirect reflect-ed radiation. The core section showed a much slower decrease at the same irradiance level. Furthermore, the OIT depletion rate in the surface layer increased with radiation intensity. The study proved that the sunlight degradation of the tested HDPE material can be accelerated by increasing the irradiation intensity based on the reciprocity law, and prediction can be made for OIT depletion rate in the surface layer under the field conditions using the weatherometer test data.