Using light-emitting diode (LED) technologies, an LED printer is piece of computer hardware which uses a non-impact method to put images and text onto paper. Like a laser printer, an LED printer uses toner and heat to accomplish this. LED printers, however, have fewer moving parts than laser printers and should, theoretically, prove to be more reliable over time.
The page image is sent to the processor of the LED printer, which controls an array of LEDs. The LEDs flash the image of the page, line by line, onto a photosensitive drum, which picks up an electrical charge where it is hit by light and then rolls into contact with the printer's toner cartridge. Toner is a fine powder that is attracted to the charged areas of the drum. The drum then rotates and comes into contact with the paper where the toner is deposited. After the paper runs through a high-temperature fuser which melts the toner onto the paper, the printed page emerges.
LED printers use an array of LED's with a single LED for every image. For example, a printer with a 600 dot-per-inch (dpi) resolution and an 8-inch (20-cm) wide printing area would have 4,800 LEDs. These are inexpensive to produce and extremely reliable, with useful lives rated in the thousands of hours. In a laser printer, the drum is illuminated by a moving laser beam the light from which passes through rotating mirrors and lenses. The complexity of this system tends to make laser printers noisier, more expensive, and less reliable.
Printer technology that uses LEDs has historically had a number of drawbacks which come from the use of a fixed array of LEDs. Manufacturing practicalities have made it hard to make small enough LEDs for LED printers to go above 600 dpi resolution, while laser printers easily exceed 1,200 dpi. In addition, because the LEDs cannot always flash on and off quickly and cleanly enough and have a tendency to sometimes produce blurry printed images which cannot match the sharpness of a laser printer.
As of the end of 2011, LED printers have output quality that is essentially indistinguishable from laser printers. In fact, because they look and act like laser printers, many retailers mislabel them as laser printers. Given this, many users have begun to unknowingly integrate LED printing technology into their homes and offices.