Digital LED printers are like laser printers in that they use toner (dry ink), static electricity and heat to place and bond ink onto the paper but their difference is in the use of Digital LED (light emitting diode) heat source technology rather than a laser, and separate toner and drum modules.
This differentiates and simplifies the multiple passes to fix the four colours in the laser alternative. In colour Digital LED printers CMYK colours are applied to the paper in a single pass.
A static charge is applied to a photo-receptive drum and, when the light from the LED hits it, the charge is reversed, creating a pattern of dots that corresponds to the image that will eventually appear on the page. After this, electrically charged toner is applied, which sticks to the areas of the drum that have had their charge reversed, and the toner is then applied to the paper as it passes the drum on its way to the output tray.
The difference between the two technologies lies in the method of light distribution and how many passes the paper has to make through the system to print the four colours.
LED printers function by means of an array of LEDs built into the cover of the printer usually more than 2,500 covering the entire width of the drum - which create an image when shining down at 90 degrees. A 600 dpi LED printer will have 600 LEDs per inch, over the required page width.
The advantage is that a row of LEDs is cheaper to make than a laser and mirror with lots of moving parts and, consequently, the technology presents a cheaper and potentially more reliable alternative to conventional laser printers. The LED system also has the benefit of being compact in relation to conventional lasers.
The compactness which results from use of LED arrays instead of the bulky focusing paraphernalia associated with a laser imaging unit allows the colour engine to be built with four complete print heads arranged. Colour LED printers have four rows of LEDs - one each for cyan, magenta, yellow and black toners - allowing colour print speeds the same as those for monochrome units.
The CMY and K toner cartridges are laid out in-line down the paper path and each unit has its own photo-conductive drum. Above each unit in the printer's lid are four LED arrays - again, one for each colour. Data can be sent to all four heads simultaneously.
The process starts with magenta and passes through cyan and yellow, with black laid down last. This process has a dramatic advantage over laser in speed and application as a result.
