Definition: laser printer

A printer that uses a laser and the electrophotographic method to print a full page at a time. The laser "paints" a charged drum with light, to which toner is applied and then transferred onto paper (see electrophotographic for more details). Desktop laser printers use cut sheets like a copy machine. Large printers may use paper rolls that are cut after printing.

Resolution and Features
Laser printer resolution is typically from 300 to 1200 dpi, but specialty printers can reach imagesetter resolution of 2400 dpi. Options such as duplex printing (both sides) as well as collation, stapling and 3-hole punching may be available.

Small, Medium and Large
Low-end laser printers print in the 4 to 8 ppm range, while typical office workgroup units print 17 to 32 ppm. Midrange units print in the 40-60 ppm range, with a large jump to high-end printers that print from 150 to more than 1,000 ppm.

Color
Color lasers are slower than their monochrome counterparts, typically in the 4 to 10 ppm range. At the other end of the spectrum, high-end "digital printing presses" can print 70 or more duplexed color pages per minute, producing finished booklets and manuals. See color laser printer and digital printing.

Laser-Class
There are several technologies that fall into the laser category, but do not actually use a laser. LED printers use an array of LEDs to beam the image onto the drum, and electron beam imaging (ion deposition) creates the image with electricity rather than light. Solid ink printers propel a waxlike ink onto the drum.

History
In 1975, IBM introduced the first laser printer, the model 3800. Later, Siemens came out with the ND 2 and Xerox with the 9700. These self-contained printing presses were online to a mainframe or offline, accepting print image data on tape or disk.

In 1984, HP introduced the LaserJet, the first desktop laser printer, which rapidly became a huge success and a major part of the company's business. Desktop lasers made the clackety daisy wheel printers obsolete, but not dot matrix printers, which are still widely used for labels and multipart forms.

The Laser Mechanism

The laser printer uses electrostatic charges to (1) create an image on the drum, (2) adhere toner to the image, (3) transfer the toned image to the paper, and (4) fuse the toner to the paper. The laser creates the image by "painting" a negative of the page to be printed on the charged drum. Where light falls, the charge is dissipated, leaving a positive image to be printed.

The LaserJet

Noisier than today's models, but built like a tank, HP created a revolution in desktop printing with its 1984 introduction of the LaserJet. The LaserJet's reliability became legendary and caused HP to become the world leader in desktop laser printers. (Image courtesy of Hewlett-Packard Company.)

Midrange Laser Printer

This Dataproducts printer prints up to 60 ppm and uses a unique drum system. The unit does not have to be stopped except once each 100,000 pages to advance the drum sleeve. The drum lasts for a million pages, because it contains 10 sleeves in the cylinder. (Image courtesy of Hitachi Koki Imaging Solutions, Inc.)

Continuous Forms Laser Printing

This Printronix printer uses continuous forms. Continuous forms printers provide tighter registration over cut sheets and support non-standard paper sizes. In addition, a huge amount of paper can be printed without operator intervention. (Image courtesy of Printronix, Inc.)

The Versatile Network Printer

This Xerox printer offers paper handling options, including an envelope feeder (middle) and private collator (top) that keeps sensitive documents locked in bins that must be opened with a password. (Image courtesy of Xerox Corporation.)