A photomultiplier tube assembly for the detection of low light levels.

Bioluminescent indicators have found many uses in, for example, the detection of ATP and free calcium levels. However, such probes often emit only very low levels of light and it is important to optimize the efficiency of the system used to detect this light. We describe some of the problems encountered in using photomultiplier tubes for detecting low levels of light, and some ways of overcoming these problems. We have developed a versatile photomultiplier light detection system which is both efficient and physically small. This system is described and details of its fabrication are given.