Fluorimetry involves measuring fluorescence intensity at a particular wavelength using a fluorimeter or spectrofluorimeter. Fluorescence occurs when molecules absorb radiation and electrons are excited to a higher energy state. As electrons return to the ground state, they emit radiation. Factors like concentration, pH, and temperature can affect fluorescence intensity. Instrumentation includes a light source, filters/monochromators, sample cells, and detectors. Applications include determining inorganic/organic substances and compounds in pharmaceutical analysis.