ABSTRACT
INTRODUCTION Several types of spectra are referred to in the pharmaceutical photostability literature, including emission, absorption, activation, action, and spectral power distributions (SPDs). Each of these terms has a specific meaning and use. For example, the absorption spectrum of a typical compound is often assumed to represent its degradation sensitivity, which is not always the case. This assumption arises because of the fact that in order for a compound to react with radiation, it must first absorb it and a good first indicator of these active wavelengths are its absorption spectra.
