Gap-dependent species are typically understood to have higher population growth rates (λs) when they are exposed to higher light transmittance. I investigated the relationship between both diffuse light and direct light transmittance and λ for the gap-dependent plant Trollius laxus using 5 years of data from 20 subpopulations (11 in created, experimental canopy gaps; 9 in intact canopy control areas). There was a nonlinear (unimodal) relationship between diffuse light and λ for T. laxus under the wide range of light levels encountered at the gap and control subpopulations [4–58 % diffuse photosynthetic photon flux density (PPFD)]. There was no relationship between direct light and λ. However, in the gaps, where light levels were generally greater than 20 % PPFD, both diffuse light and direct light had strong negative linear relationships with λ. Therefore, under wide-ranging light regimes, plant populations may show complicated, nonlinear responses to gap formation. Furthermore, gap-dependent plant populations may even decline in the brightest gaps. These results demonstrate that future studies on forest plant population dynamics should strive to include populations from a wide variety of light regimes, and avoid broadly categorizing light regimes as simply “gap” or “non-gap.”