This paper describes a new method of bias-lighting suitable for ultra-high sensitive HARP tube camera. It is estimated that by the conventional method of bias-lighting, the shot noise of the bias light deteriorates the signal-to-noise performance when the sensitivity of HARP camera is made much higher. But considering the optical absorption and multiplication characteristics of a-Se, it is concluded that the deterioration can be eliminated by giving some short-wavelength light from the beam scanning side of the tube as bias light.
