This work deals with the issue of the light emission that took place during the Tunguska catastrophe of 1908. According to eyewitnesses, after the disappearance of the flying object over the horizon, a column of light rose above the place of its fall. This pillar was visible on a sunny morning from a distance of ∼500 km and reached a height of ∼80 km above the ground. The duration of the existence of this column of light was estimated at 6–7 s. The thermal effect of radiation from this column was great: at a distance of ∼30 km from the epicenter, live needles caught fire, and at a distance of 65 km, the effect was close to a burn of human skin. The model of the radiation source is most consistent with the level of thermal impact on the environment if this source was located at an altitude of 30 km above the ground. According to estimates, the energy of this radiation exceeded 5·1022 erg. This work discusses the assumption that during the Tunguska catastrophe there was a powerful upward atmospheric discharge, which was a consequence of the formation of numerous relativistic runaway electron avalanches.