Digital light processing (DLP) and liquid crystal display (LCD) 3D printing have similarities to stereolithography (SLA) 3D printing; each of these technologies uses a light source to cure the resin. A projector is used to cure photopolymer resins in DLP printing and UV LEDs are projected through and LCD screen for LCD 3D printing.
The process of printing using these technologies can be “top-down” or “bottom-up”. In “top-down” printing, the object being printed is lowered into the resin and returns to one layer lower than previous after each layer is cured. In “bottom-up” printing, the object being printed is pulled out of the resin and returns to one layer higher than the previous after each layer is cured. The process is repeated layer by layer until the shape is built.