Notan is a Japanese word meaning dark-light. The word, however, means more than that. The principle of Notan as used here must be further defined as the interaction between positive (light) and negative (dark) space.
The idea of this interaction in Notan is embodied in the ancient Eastern symbol of the Yang and the Yin, which consists of mirror images, one white and one black, revolving around a point of equilibrium. Here the positive and negative areas together make a whole created through a unity of opposites that have equal and inseparable reality. In the Yang and the Yin symbol, as in Notan, opposites complement, they do not conflict. Neither seeks to negate or dominate the other, only to relate in harmony. It is the interaction of the light and the dark, therefore, that is most essential.
Dorr Bothwell and Marlys Mayfield
“Notan: The Dark-Light Principle Of Design”