While ambipolar (a-) CNTFETs may be undesirable in logic applications, they can be particularly valuable in photonics. Earlier we have shown that when electrons and holes are injected from the opposite terminals of an a-CNTFET, a fraction of them recombine radiatively generating an electrically-excited single nanotube light source. Unlike conventional p-n diodes, however, a-CNTFETs are not doped and there is no fixed p-n interface. Through spatially resolved measurements we will show that the emission can be translated along the CNTFET channel by varying the gate voltage. Study of the properties of the emission as a function of applied bias provides new insights on the electrical transport in CNTs. Stationary light spots are also observed and their generation mechanism will be discussed. Finally, single CNT photoconductivity spectra and theoretical modeling will be used to prove the excitonic nature of the excited states of the CNTs.