Abraham Loeb and Edwin Turner, scientists from the United States, have proposed a new criterion for the search for Extraterrestrial civilization, which is based on an analysis of the spectral radiation in the visible range of electromagnetic waves. Scientists have noted, that the spectrum of artificial light is very different from the spectrum of radiation of the stars and planets of the spectrum of reflected light, so that an extraterrestrial civilization can be found, if can find the spectral lines, which are inherent in the artificial light is the light that comes to Earth from the stars. Likewise, the aliens could find credible evidence that on Eearth there is a civilization, based on the detection of significant differences between the solar spectrum, the spectrum of the reflected light from the other planets in our solar system and the spectrum of the Earth, where the night lights of big cities of the Earth stands out among the Earth's spectrum range of other planets in the solar system.