The energy spectrum of cosmic rays above 10^15 eV as derived from air Cherenkov light measurements in Yakutsk

The Yakutsk array observes the Cherenkov light emitted by UHECR in atmosphere. Recently, an autonomous subarray is added consisting of photomultipliers to measure the showers in the knee region. Our aim is to analyze the combined data set in order to derive the cosmic ray spectrum in the energy range as wide as possible using the same technique. The advantage of the air Cherenkov light measurement is the model independent estimation of the EAS primary energy using the total light flux emitted in the atmosphere. A set of the light lateral distributions observed in the extended energy range is presented also