text: LD is very similar to Circular Dichroism (CD), but with two important differences.  (i) CD spectroscopy uses circularly polarized light whereas LD uses linearly polarized light. (ii) In CD experiments molecules are usually free in solution so they are randomly oriented. The observed spectrum is then a function only of the chiral or asymmetric nature of the molecules in the solution. With biomacromolecules CD is particularly useful for determining the secondary structure. By way of contrast, in LD experiments the molecules need to have a preferential orientation otherwise the LD=0. With biomacromolecules flow orientation is often used, other methods include stretched films, magnetic fields, and squeezed gels. Thus LD gives information such as alignment on a surface or the binding of a small molecule to a flow-oriented macromolecule, endowing it with different functionality from other spectroscopic techniques.  The differences between LD and CD are complementary and can be a potent means for elucidating the structure of biological molecules when used in conjunction with one another, the combination of techniques revealing far more information than a single technique in isolation. For example, CD tells us when a membrane peptide or protein folds whereas LD tells when it inserts into a membrane.