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