An Aston dark space is a dark space in a glow discharge which is adjacent to the cathode.

Because it absorbs visible light.

The cathode space charge is determined by the voltage on the filament.

The negatively charged electrode of a cathode ray tube (CRT) is the cathode. The tube is a cathode ray tube, and electrons stream off the cathode, are accelerated across the evacuated space and "directed" either electromagnetically or electrostatically, and then strike the phosphor coating on the positively charged anode at a "location" determined by the "directing" elements.

Negative space is dark energy and dark matter.