Instrument: Fluorometer
A fluorometer or fluorimeter is a device used to measure parameters of fluorescence: its intensity and wavelength distribution of emission spectrum after excitation by a certain spectrum of light. The instrument is designed to measure the amount of stimulated electromagnetic radiation produced by pulses of electromagnetic radiation emitted into a water sample or in situ.
Turner Designs' PhytoFlash is an active fluorometer that measures quantum efficiency of photosynthesis.
Fore more details see the PhytoFlash page: http://www.turnerdesigns.com/submersible?page=shop.product_details&flypage=flypage_default.tpl&category_id=1&product_id=4