A detection apparatus for use in printing devices is disclosed including a container for storing a printing composition, a light source, a light detector, and a light waveguide. The waveguide conducts light from the source to the detector which is configured to enable printing by the device when the...http://www.google.de/patents/US6097405?utm_source=gb-gplus-sharePatent US6097405 - Detection apparatus and method for use in a printing device
