The Wanhao Duplicator 7, or D7, is a DLP 3D printer. DLP (Digital Light Processing) printers operate by projecting an image onto a build plate, curing layer after layer of photosensitive resin to form the printed object. The D7, in particular, operates using an array of UV LEDs and an LCD screen which acts as a mask, blocking the light from areas that are not to be printed.
The advantage of DLP and SLA (a related technology) printers is that they both allow for high resolution prints, producing an excellent representation of your model. The disadvantage is that the printing media, liquid photosensitive resin, can be both difficult to work with and can be quite expensive when compared to plastic filament for FDM printing.
A general safety overview of working with resin printers