In this study we performed a random-effects comprehensive meta-analysis of data published by various studies that investigated passively (solar) and actively (artificial light) induced chlorophyll fluorescence (F) in a steady state as an indicator of various stress events. Specifically, we reviewed and analysed behaviour of the steady-state fluorescence in red (684-695 nm, FR) and far-red wavelengths (730-740 nm, FFR), and also their ratio (FR/FFR), for plants physiologically stressed by water deficiency, temperature extremes (chilling and heat) and nitrogen insufficiency. The meta-analysis was followed by systematic investigation of knowledge gaps between actual scientific understanding and potential application of remotely sensed steady-state F as an early indicator of plant stress. The knowledge gap analysis pointed out that the lack of dedicated studies assessing measurement errors caused by the factors interfering with F measurements is currently the weakest point of the chlorophyll fluorescence stress detection discussion. The largest identified gap, common to all three investigated stressors, is potential use of the steady-state F signal acquired at the level of whole ecosystems with complex heterogeneous canopies that are naturally established as mixture of various plant functional types (e.g., grassland with shrubs and trees). The most challenging unknown is behaviour of F under the influence of combined multiple stress impacts and the related temporal aspects. The least is known about the potential use of F emissions as indicators of plant nitrogen insufficiency, due to the multiple roles of nitrogen in plant physiological processes. Systematically coordinated experiments of active F measurements physiologically linked to passively observed F are suggested to bridge the identified gaps. Regular measurements at permanent research sites forming a global network may help us to establish an envelope of plant environmental limits, for which F values are stress indicative. Finally, measurement of both FR and FFR signals can be strongly recommended, as these measurements seem to be complementary rather than redundant and their ratio demonstrated a consistent stress indicating character.