An approach for joint optimal design system parameters is considered for energy efficient cluster-based spectrum sensing in cognitive radio (CR) networks. The design problem is formulated and subjected to primary user protection constraints and spectrum utilization requirements. An iterative algorithm with low computational complexity is proposed to determine joint optimal sensing time, data transmission time, and the number of CR users that maximize energy efficiency of the system. The design criterion combines two design parameters, namely, sensing time and data transmission time, into one parameter in order to reduce the complexity. The key idea of the proposed algorithm is to employ the impact of transmission power variation on both the optimal sensing time and the corresponding probability of false alarm. The performance of the proposed algorithm is presented and evaluated through simulation results.