What is the difference between DPI and LPI in printing?

DPI counts the dots per inch a device can address or an image supplies, while LPI counts the rows of halftone dots per inch that the screening actually builds from those device dots. A device therefore needs a DPI figure several times higher than the LPI it prints at, because many device dots are used to construct each halftone dot. Increasing file DPI beyond what the screen ruling can resolve adds file size and nothing else.