The analysis of chlorophyll-a fluorescence in plants is a valuable tool for gaining insights into plant physiology, photosynthetic performance, and potential alterations at the level of photosystems I and II. One method of recording fluorescence involves measuring the emitted intensity as a function of wavelength. These spectra are typically obtained under steady-state conditions, where the spectrum remains constant over time, unaffected by variable fluorescence induction. At room temperature, the fluorescence spectrum of chlorophyll-a in plants is characterised by two bands: one in the red region due to the emission of photosystem II and one in the far-red region linked to emissions from both photosystems. The ratio of the red to far-red peaks has been correlated with the presence of biotic and abiotic factors in the environment. However, fluorescence originating at the chloroplast level undergoes light re-absorption and re-emission processes within the plant leaves. Shorter wavelength photons are more likely to be absorbed by the tissue than longer wavelength photons, leading to a distortion in the signal recorded outside the leaves. This phenomenon also occurs at the canopy level. The plant physiology relates to the original spectrum emitted by the chloroplast, not to the distorted spectrum observed externally. Therefore, it is essential to correct the experimentally observed spectra for these re-absorption and re-emission processes. This chapter describes physical models for correcting both the spectral distribution of fluorescence and the fluorescence quantum yields.