In recent days wireless network provides a high bandwidth support eternally for enabling a loss free communication. One amongst the standards available for high rate support in personal area network is WiMedia Ultrawideband. It provides consumer applications and products at low price consuming low energy. An effective slot allocation and scheduling method could enhance the performance of the existing system. This article presents an optimal medium access slot allocation considering the residual energy among the competing devices using firefly algorithm. Further this article investigates the effect of energy in slot allocation and resulting throughput which influences the network lifetime. Firstly, the procedure to select the nodes with highest residual energy amongst the competing nodes to allocate the free slot is presented. Next, the impact of the result is analyzed. © 2017 IEEE.