High intensity runway lights become invisible when the optical thickness (τ ) of the atmospheric layer between the light and an observer is 3 or more (up to 10 at night time), while the lidar operation range corresponds to value of 1.5 to 2. In this case an assumption seems to be justified that the mean extinction coefficient measured in an atmospheric layer h is independent on the elevation angle. This basic assumption has been checked in a long series of the lidar observations.