The fabrication and characterisation of LED structures made of Ge grown on Si substrates is reported. The structures are circular mesa of strained n-Ge etched down to an undoped buffer of Ge. The electroluminescence exhibit average power levels at 1.7 um of a few uW, many orders of magnitude larger than the nW previously reported. 3 individual mechanisms of emission are identified which can be used to interpret the results encountered in other publications. This work potentially opens the route for integrated source of light and photo-detectors above 1.6 um on Si with applications for lab-on-a-chip and healthcare.