The investigation of the kinetics of chlorophyll-fluorescence under continuous background light enables the application of linearizing conditions. This approach, which provides a quantitative evaluation by means of curve-fitting routines, is applied to the investigation of the linear kinetics of the I-D-P phase. Using changes in PS II-light, PS I-light and in CO2-concentration as input signals showed that a pool at the acceptor side of PS I, in addition to the plastoquinone pool, plays an essential role in the generation of the dip. The occurrence of the dip is related to the sign of the faster one of the two components related to the I-D and the D-P phase. This sign can be inverted by the ratio of PS I and PS II light. However, model calculations show that the change of this sign does not allow a decision which one of the two components is related to which one of the two pools. The dependence of the sign of the faster component on light conditions can generate different types of I-D-P transitions, namely nearly monophasic increases, sigmoid responses or dips. As these phenomena are already created by the linear responses, non-linear effects or additional loops between PS II and PS I are not required for the explanation of the basic features.