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We have studied both the spectral intensity and the energy of radiation produced by an electron beam in dielectric medium. Since the device starts up from a photon vacuum the investigation is based on a quantum electrodynamics approach. We have assumed that the electron beam longitudinal size is indefinite and its energy spread is of Gaussian form. In such a case the radiation process has a cutoff with respect to the electron density 0 . If the electron density is lower than some characteristic density ch then the radiation will be mainly spontaneous and its emission line will have Gaussian shape. If the electron beam is dense, 0 Ͼ ch , then a drastic change of line form takes place. Namely, one observes a high and narrow peak ͑or superradiation effect͒ on its right-hand side and radiation energy saturation on its left-hand side. Both of these phenomena are due to the stimulated processes of photon absorption and emission. We have evaluated the level of radiation fluctuations in the peak vicinity. Numerical estimations of both obtained effects are presented.

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