A stable, inexpensive and easily constructed photometer consisting of a cercial intergrated photodetection assembly, complementary solid-state operational amplifiers and a solid-state power supply for use in the detection and quantification of low level light emissions from bioluminescence organisms...http://www.google.com.hk/patents/US4689305?utm_source=gb-gplus-share專利 US4689305 - Solid-state photometer circuit
