In this paper, we evaluate the energy efficiency of today's radio chips for wireless sensor nodes. We compare the energy needed for node-to-sink communication using different transmission powers. We show that for a network without data aggregation in which nodes are spread homogeneously, increasing transmission power reduces the energy consumed by the network in almost all practical circumstances. We show that these conclusions can be generalized for networks with data aggregation, and heterogeneous spreading of the nodes and power levels. We conclude that for today's radio electronics applying the low transmission powers is only useful for a wireless sensor network under very specific conditions.