Lighting constrained visible-light communications are expected as indoor communications of next generation. In lighting constrained visible-light communications, lighting devices are used not only for illuminating rooms but also for optical wireless communications. For lighting constrained visible-light communications, we have been proposed a variable N-parallel code-shift-keying (VN-CSK) using a modified prime sequence code (MPSC). The VN-CSK system using MPSC has not only a suppression function for reducing co-channel interference from neighboring lighting devices, but also a function for keeping constant data transmission regardless of dimming control. In this paper, the bit error rate (BER) of the VN-CSK system using MPSC is derived under an indoor visible-light communication channel by theoretical analysis. Moreover, we evaluate the BER performance for the brightness level (dimming control stage).