Compound light microscopes use either transmitted or reflected light to illuminate an object. A number of observation techniques have been developed for light microscopy, including bright field, dark field, fluorescence, phase

contrast, interference contrast, and polarization, among

others. In the identification of crude drugs, details are

usually visible with a bright field transmitted-light micro-

scope, which is the typical microscope found in biology

classrooms. The specimen is placed on a clear glass slide

and light is transmitted through it, making the object visi-

ble against a bright background. A polarization tool to sup-

port the detection of certain structures (calcium oxalate,

elements with thickened walls, and starch) is also useful.