The effect of small scale structural dynamics of forest stands and their canopies on spatiotemporal heterogeneity of the understory light regime was assessed in this study. Forest structure and woody species composition in combination with canopy structure parameters and photosynthetic photon flux density (PPFD) were measured in three investigation plots. Sampling took place during two periods in 2004 and 2005 to check on inter-annual differences of canopy conditions and light availability. All plots differed considerably in species composition and high -diversity was recorded. Forest structure and canopy openness differed between plots. No differences in leaf area estimations and photon flux density were found during the same sampling period. Inter-annual differences were identified for leaf area index and canopy openness, but not in conjunction. On the other hand, inter-annual differences in photon flux density were only identified in combination with significant canopy openness changes. Our study confirmed hemispherical photography and quantum sensor based PPFD measurement as a valid tool for rapid assessment approaches regarding canopy structure and their spatiotemporal heterogeneity and the effect on understory PPFD fluctuations. The variability and heterogeneity of canopy structure may help to explain the impact on stand dynamics and the reduced importance of classic gaps in communities identified for some rainforests.