Biological invasion by nonnative species is considered one of the major threats to the global environment. Amur honeysuckle (Lonicera maackii) is a shrub introduced from Asia which has become invasive in Eastern deciduous forests of North America. An interesting aspect of the life-history of Amur honeysuckle is its extended leaf phenology. It leafs out earlier in the spring than most native shrubs and understory trees and loses its leaves later in the fall. Thus, Amur honeysuckle has the potential to alter the natural light environment and possibly impact native species, particularly spring ephemerals which are dependent on high light levels prior to canopy leaf-out. We tested the hypothesis that light levels are lower in sites with Amur honeysuckle relative to sites with native forest understory and quantified differences between sites. We found that light levels were significantly lower under Amur honeysuckle compared to natural understory, with the greatest reduction occurring during spring. Temperature at ground level was also lower under Amur honeysuckle than under the natural understory during spring. The extended leaf phenology of Amur honeysuckle alters both temperature and light intensity, which may increase both its success as an invader and its impact on native species.