photodynamics

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The science that deals with the effects of light on molecules, especially the activating effects of light on molecules that are inserted into the body to treat disease.
• noun The behavior of a substance or chemical when exposed to light.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Plant Physiol.) The relation of light to the movements of plants and their organs; the study of the phenomena of curvatures induced by the stimulus of light.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The study of the activating effects of light on living organisms