A sensing system is described for detecting the presence of ink at a predetermined level in an ink reservoir for an ink jet printer. The reservoir includes a perimetric wall having first and second wall sections, wherein at least a portion of said first wall section and a portion of the second wall section are substantially transmissive to light. A light emitter is located proximate to the first wall section and positioned at the predetermined level. A photo detector is positioned at the predetermined level and located proximate to the second wall section for detecting the light emitted from the light emitter, the light emitter being oriented to direct light at the photodetector. The light from the light emitter follows a first path when ink is present in the reservoir at the predetermined level and follows a second path when ink is not present in the reservoir at the predetermined level, the photodetector receiving the light from the light emitter traveling only one of the first path or the second path.