Evolution of the mass-to-luminosity ratio in the optical (upper row) and NIR (lower row) and various population effects. The curves shown in the left and middle panels present SSP models with continuous IMF, in the right panels we compare continuous-IMF and discrete-IMF cases. The left panels show the influence of cluster mass loss owing to dynamical evolution for clusters of different initial masses with stellar low-mass limit m_l = 0.1   m_⊙. The curves are artificially shifted vertically in order to avoid crowding as shown by cyan arrows. The upper (shifted up) curve corresponds to the initial mass of M_c = 10⁴   m_⊙, the middle (shown in the original position) curve is for M_c = 5  ×  10³   m_⊙, and the lower (shifted down) curve corresponds to M_c = 10³   m_⊙. The dotted portions (as everywhere in this figure) mark models without mass loss. The middle panels show the effect of variations of the lower mass limit of stars for a model of M_c = 10³   m_⊙. The upper, middle, and bottom curves correspond to m_l = 0.01, 0.1, 1   m_⊙, respectively. In the right panels we compare models with continuous IMF (curves) and discrete IMF (connected symbols) for clusters of different masses with m_l = 0.1. Crosses indicate models with M_c = 10⁴   m_⊙, triangles M_c = 5  ×  10³   m_⊙, and diamonds M_c = 10³   m_⊙. As in the left panel, the curves for different M_c are artificially shifted vertically in order to avoid crowding.