  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.
