An analytical method to investigate the characteristics of the visible-light positioning using received signal strength (RSS) is proposed, and the formation mechanism of the positioning error is explored. The positioning error is studied in terms of two contributing factors being the original measurement noise of RSS and the dilution of precision (DOP), which transforms the measurement error to the positioning error. It is found that the DOP is related to light-emitting diode (LED) parameters, receiver parameters, and the geometric deployment of the LED beacons. In particular, the LED beacon geometric deployment in the form of triangle, square, and hexagon cell geometries are characterized and optimized. Numerical results show that the mean positioning error of the triangle deployment is smaller than the other two geometries under the same condition, and the side length of the cell should reduce as the half power angle of the LED decreases. The results of this paper provide a guideline to design the RSS-based visible-light positioning (VLP) systems.