Patent ID: 8333461

Claim:
An ink cartridge for an inkjet printer, comprising an ink supply port, an air vent, an ink chamber for accommodating ink to be supplied to the printer and a light detection portion, wherein the light detection portion comprises a first triangular prism and a second triangular prism, the second triangular prism is formed by transparent material, the first triangular prism has a first surface and a second surface for reflecting light emitted by a light emitting element, the second triangular prism has a second surface and a third surface, the first surface and the second surface of the first triangular prism are aligned with the second surface and the third surface of the second triangular prism, respectively, so that the light is reflected onto the second surface of the second triangular prism by the first surface of the first triangular prism when the light is emitted by the light emitting element onto the first surface of the first triangular prism, wherein when the ink cartridge contains sufficient ink, the second surface of the second triangular prism refracts the light reflected from the first surface of the first triangular prism into the ink, and when the ink in the ink cartridge is exhausted the second surface of the second triangular prism reflects the light reflected from the first surface of the first triangular prism onto the third surface of the second triangular prism.