Recently, a new way of studying photosynthesis by remote sensing have been discovered, through the solar induced CHolorophyll Fluorescence (ChlF). In this paper, we review the main concepts and mechanisms used to retrieve ChlF by remote sensing. This includes space-based approaches, whose ChlF retrieval is more difficult to be achieved mainly due to atmospheric and sensors limitation issues, that can be mitigated with the launch of the FLEX mission. In addition, a set of ChlF data from the Gome-2 sensor and incident radiation reanalysis data from GLDAS, spanning the 2007-2015 period, were used to analyze the relationship between photosynthesis and radiation seasonality in the Amazon forest by decomposing the original data through the BFAST algorithm. The maximum incident radiation is observed from August to October in most part of the Amazon forest. On the other hand, the maximum photosynthesis activity occurs mainly from September to December. The photosynthetic activity increased after incident radiation raised, with a time-lag varying from one to three months, potentially related to the production of new leaves after the vegetation perceived the increase in the radiation signal. Photosynthesis seasonality thus varies spatially and seems to have a strong relation with radiation signals in the Amazon forest.