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Since indoor visible light communication (VLC) modulates the information into the light beams emitted from light-emitting diodes, the channel gain is often modeled as the Lambertian model. For different spatial locations of transmitters and receivers, the channel gain for VLC directly changes with several related geometrical parameters. The distinct geometrical feature makes the ergodic capacity of indoor VLC different from that of radio-frequency communication. However, the issue has not been studied currently. In this paper, we propose the lower bounds on the point-to-point capacity, which have simple expressions with respect to the geometrical parameters. Then, by analyzing indoor human mobility, two typical distributions of the geometrical parameters are considered. Correspondingly, we derive the lower bounds on the ergodic capacity, which are related to the variables of the geometrical feature and the distribution model. Furthermore, simulation results show that our lower bounds on the ergodic capacity are effective to reveal the geometrical feature of indoor VLC systems. Moreover, our proposed lower bounds are tight to the numerical upper bounds at high optical signal-to-noise rates, which are the main application zones of indoor VLC systems.