We present a state-of-the-art ultraviolet (UV)-based multiuser indoor communication over power-constrained discrete-time Poisson channels. To adhere to the UV exposure limit and safety, we consider a low-power transmission regime where strict peak and average transmit power constraints are imposed. These constraints are different from conventional electrical power constraints. Therefore, performance metrics, such as bit error rate (BER) and channel capacity, are newly characterized in relation to the discrete-time Poisson channel. We develop a minimum mean-square error receiver to reject the interference from multiple users with a detection scheme robust against channel state information (CSI) uncertainty. Furthermore, a downlink beamforming optimization problem is formulated using a second-order cone program to maximize the received signal-to-interference-plus-noise ratio. We bound the behavior of the mutual information in the low-power regime, when dark current increases linearly with average transmit power. In addition, the power penalty of multiuser link is analyzed. The proposed system is also realized in the experiment. The influence of the control parameter, i.e., average-to-peak power ratio, on the BER relative to the peak transmit power is experimentally investigated. The experimental results are found consistent with the theoretical simulation results. Further, from the simulation results, it is found that the proposed system approaches the CSI lower bound performance with a minimum sequence length and can provide ubiquitous link connectivity in indoor applications while keeping network structure and management simple.