Patent ID: 7862161

Claim:
An ink cartridge configured to hold an ink, the ink cartridge comprising: a substantially hollow body including an inner space and a substantially continuous inner wall; and an optical prism in the inner space of the body, disposed at a predetermined distance from the continuous inner wall such that a prism wall and the continuous inner wall of the ink cartridge define an ink pocket, the optical prism including at least one reflection site formed at an angle configured to reflect light from a light source through the optical prism at a predetermined height of the optical prism relative to a bottom of the hollow body; wherein, if the ink is present in the ink pocket at a level below at least a portion of the at least one reflection site, the ink does not block the light reflected off of the at least a portion of the at least one reflection site from traveling across the ink pocket at the predetermined height, such that the reflected light is externally viewable.