An apparatus comprising a variable aperture for controlling electromagnetic radiation and related systems and methods are described. In one aspect, a variable aperture to control electromagnetic radiation comprises a first substrate, a second substrate, an attenuation fluid, at least one charging electrode, and at least one displacing electrode. The second substrate is located opposite the first substrate and spaced apart from the first substrate to form a gap between the first substrate and the second substrate. The attenuation fluid is located in the gap and configured to absorb electromagnetic radiation of a predetermined wavelength. The at least one charging electrode is in electrical contact with the attentional fluid. The at least one displacing electrode is located on a surface of the first substrate facing the gap or on a surface of the second substrate facing the gap.