The Fluorescent Multilayer Card (FMC) is a hypothetical memory card technology that applies the same 3D optical data storage mechanism as the Fluorescent Multilayer Disc. The concept was developed by Constellation 3D. An FMC has a square, transparent window with multiple layers beneath it. Each layer is made of a different fluorescent material that emits light; each layer emits light of a different color (wavelength). An FMC reader could distinguish one layer from another by the wavelength, and therefore read from them without the problems that limit the number of layers in a DVD. Constellation 3D estimated that a card with a data area of could hold 10 gigabytes of data.