The 1880s saw the spread of large scale commercial electric power systems, first used for lighting and eventually for electro-motive power and heating. Systems early on used alternating current and direct current. Large centralized power generation became possible when it was recognized that alternating current electric power lines could use transformers to take advantage of the fact that each doubling of the voltage would allow the same size cable to transmit the same amount of power four times the distance. Transformer were used to raise voltage at the point of generation (a representative number is a generator voltage in the low kilovolt range) to a much higher voltage (tens of thousands to several hundred thousand volts) for primary transmission, followed to several downward transformations, for commercial and residential domestic use. Between 1885 and 1890 poly-phase currents combined with electromagnetic induction and practical AC induction motors were developed.