Do modern projector used for digital class works on same old conventional intermittent mechanism and blocking of light during change of frame. What is principal used in modern projector?
Modern digital projector use a technique called DLP(digital light processing). They use an array of micromirorrs in order to point the white light source(often a bulb) that goes through a filter to become colored (red, green or blue). There is a mirror for each pixel and it direct light to the projecting lens or to an absorber depending on if the pixel should be on or not.
Here you can find a nice explanation, also YouTube is full of videos https://electronics.howstuffworks.com/dlp2.htm