We describe an absolute energy efficiency metric (measured in dBε) that can be universally applied to any ICT system, subsystem and component. It shows what energy efficiency improvements are possible for any data processing/transmission/storage system. The metric’s versatility is also displayed by applying it to biologically based and quantum-level information systems. As an exemplar, we identify ten different and independent approaches, each of which on its own could achieve at least a 50% energy efficiency saving, so as to enable a thousand-fold (i.e., 30 dB) improvement in overall energy efficiency in photonic telecommunications networking.