Decision-feedback equalization is considered for point-to-point multiple-input multiple-output visible light communication systems. Based on the geometric mean decomposition (GMD) and uniform channel decomposition (UCD), two precoders under the signal non-negativity and total average power constraints are designed for such systems. The GMD scheme can decompose the channel into multiple parallel sub-channels with equal gains. The UCD scheme further improves performance through power allocation. Simulation results of bit-error-rate and capacity are presented. It is shown that the proposed schemes can outperform conventional linear designs and the UCD scheme performs better than the GMD scheme.