Dyes change their absorption curve when exposed to an electric field. The conditions under which this effect can be made large enough for application to light modulation are discussed. Theoretical expectations correspond with recorded curves of a test sample.
J. K. Fischer, D. M. von Brüning;, and H. Labhart, "Light modulation by electrochromism," Appl. Opt. 15, 2812-2816 (1976)