Linear dichroism (LD) is dichroism involving linearly polarized light. As a technique, it is primarily used to study the functionality and structure of molecules. LD can be defined as the difference between absorption of light polarized parallel and polarized perpendicular to an orientation axis. LD measurements are based on the interaction between matter and light and thus are a form of electromagnetic spectroscopy.
This effect has been applied across the EM spectrum, where different wavelengths of light can probe a host of chemical systems. The predominant use of LD currently is in the study of bio-macromolecules (e.g. DNA) as well as synthetic polymers.