3LCD is the technology that powers the majority of all education, business, and home theater projectors.
Glass is affixed to the panel to prevent damage to the TFT substrate and the adhesion of dirt. Dust isn't visible on the dust-proof glass because it is out of the range of focus when projected.
3LCD is a marketing organization created and run by Seiko Epson Corporation to promote 3LCD technology and educate consumers about its benefits. Many prominent projector manufacturers use 3LCD technology and license the 3LCD logo.