When exposed to light, plants re‐emit a small amount of light from chlorophyll molecules called fluorescence. Remote sensing instruments are now capable of measuring chlorophyll fluorescence (which is emitted between 650–850 nm) from canopies to the globe (solar‐induced chlorophyll fluorescence; SIF). A growing number of papers have highlighted an empirical linear relationship between SIF and whole‐ecosystem photosynthesis (gross primary productivity; GPP). These advances have excited the broader Earth science research community, but recent studies have pointed out that the linear SIF‐GPP relationship at coarse scales does not hold true at smaller spatiotemporal scales. In this commentary, we synthesize three recent studies that provide insight into the relationship between fluorescence and photosynthesis at leaf and canopy scales, under natural and controlled conditions. At fine spatiotemporal scales, fluorescence can be decoupled with photosynthetic carbon uptake, but we argue that satellite measurements are often too coarse in time and space to observe the SIF‐photosynthesis decoupling and that the integration of canopy processes explains the observed linearity. As such, SIF plays an important role as an estimate of GPP at spatial and temporal scales relevant for monitoring global terrestrial productivity, benchmarking terrestrial biosphere and earth system models, and managing ecosystems.