Measuring Methods for Ultra-Low Light Intensity and Their Application to Extra-Weak Spontaneous Bioluminescence from Living Tissues

This paper reports experimental and theoretical studies and their comparisons on the sensitivity of photoelectric methods for detecting very weak optical signals based on the analog and digital techniques. The single photoelectron counting and the enhanced single photoelectron counting methods were found to be advantageous over the other methods with regard to both signal-to-noise ratio and effective range for optical input powers. Furthermore, the measurements of extra-weak spontaneous bioluminescence from living tissues such as tumors and livers of mice and rats were performed as a new application of the detection methods discussed and evaluated.