Stereolithography

It all began in the 1980's when the first printing technology was created - stereolithography. It's a form of 3D printing technology used for creating models, prototypes, patterns, and production parts in a layer by layer fashion using photochemical processes by which light causes monomers and oligomers to cross-link together to form polymers. In other words, it is about converting a liquid plastic into solid objects.  However, understanding the principle of SLA helps to understand the main differences between two other methods of printing : DLP and LCD.

So,  Stereolithography (SLA) works by curing resin with UV laser. The UV laser solidifies a liquid resin layer by layer. A vat or tank contains the resin which is cured against a build platform. It thereafter slowly rises out of the tank as the object is formed.

With a Digital Light Processing (DLP) technology on the other hand, a digital light projector cures a whole layer at the time . Images of whole layers are flashed onto the bottom of the vat. Layers generated using DLP 3D printers are made up of voxels, the 3D equivalent of pixels. Indeed, in this case, the projector screen itself consists of pixels.

As for LCD 3D printing, it does not have the reputation of the two others. There is not a big difference between LCD and DLP. This technique uses LCD screen as a mask that exposes complete layers at the resin tank. However, in this case, the UV light comes from an array of LEDs and no special device is required to direct the light as it is with the previous ones.