We analyze the performance of a hybrid visible-light/infrared optical wireless communications network for indoor Internet-of-Things applications. This approach can be used to connect multiple battery-powered sensor nodes using low-cost infrared light emitting diodes to transmit data to a master node located on the ceiling of a room. The master node uses visible light communications to send back an acknowledgment and coordinate the transmission. We present a detailed model for simulating the communications layer and energy usage, which is implemented in Python and is available under an open-source license. The results indicate the suitability of this approach for sporadically transmitting low data rate signals containing sensor readings in line with the massive machine-type communication fifth generation applications.