In this paper, N parallel code shift keying (N-CSK), in which N pseudo-noise (PN) codes are selected according to the transmitted signal, is adopted as a multiple-access scheme to study Underwater simultaneous light information and power transfer (USLIPT) with multiple access. This paper proposes an inverted N-CSK scheme in which M-N unselected LEDs, which are not used as transmit signals in N-CSK, are always turned on to further improve the power supply performance while maintaining the amount of information transmitted. The performance of bit error rate (BER) and the power supply are evaluated by theoretical analysis.