Laser printers work on the principle of static electricity i.e. atoms with opposite charges attract each other. The computer or digital camera sends the matter (via a page description language PDL ) to be printed to the printer. This information is converted into dots by an internal processor.
The most important part of the printer is the photoreceptor , a revolving drum which is made of photoconductive material. This drum is given a positive charge. A laser beam is shot at it when there is a dot making that area negatively charged. The laser beam remains off when there is blank space. This is now exposed to laser toner which is positively charged. The positively charged toner pigments get attracted to the negatively charged areas of the electric drum. With one complete rotation, the drum is now covered with the required image.
Next the print media , say a paper, which is negatively charged is passed over the drum. The positively charged toner pigments now get attracted to the paper and the entire image is transferred to the paper. A fusing elementapplies heat and pressure to the paper; the toner melts and adheres to the paper.
Finally the drum is cleaned by mechanically scraping off of the toner and electrically charging the entire drum positive once more.
Laser printers have captured the black and white printing market. However color laser printers have not been able to match the quality of inkjet printers. Color laser printers use four separate color toner cartridges cyan, magenta, yellow, and black (CMYK).
The advantages associated with Laser printer are many.
• It has high speed of operation when compared with inkjets.
• The diameter of the laser beam shot is constant, resulting in more precise pictures and no ink spillage problem like in inkjets.
• No ink spillage problem that is possible in inkjets.
• Though toner cartridges cost more than ink cartridges, but they last longer. Each cartridge yields around 2,500 to 10,000 pages. So the running cost is not high.
• It is ideal for continuous text printing.
• The color laser printers can print on a variety of media as the ink is fused into the paper. Control of the final heat and pressure applied on the paper can give a finish from matte or gloss finish.
Among the disadvantages the following are noteworthy:
• High initial cost.
• Toner cartridges are expensive as they include the electric drum, developer unit, ozone filter and fuser
• The color printouts are not as good, not suitable for photography or high quality image printing.
• Relatively heavier than an equivalent inkjet printer
Technical Features to be checked before buying a laser printer:
Resolution - For normal everyday printing and small desk top publishing jobs a 600 dpi resolution will suffice. Printers with a resolution of 2400 dpi cost more. They give very sharp text output.
Low cost laser printers with 300 dpi resolution produce images with rough lines at the outer edges. Check out for those that come with Resolution Enhancement Technology (RET). This smoothens out the jagged lines at the outer edge of an image by inserting dots at the edges of lines.
Speed - Speed of printers is expressed in pages per minute (ppm). The ppm for printing black and white pages is four times faster than required for printing color pages. This is because most color lasers print black and white in one pass, but for color documents in four passes.
Home and personal use printers which require printing an average of 200 pages per week can be bought at $200. Speed of such low end printers is typically around eight ppm.
For business purposes and offices where the requirement is about 1000 pages per week, higher speed printers would fit the bill. These printers have speed up to 24 ppm and the price can be anywhere in the range from $1000 to $6000.
Production house printers can cost $10,000 and up, with print speed of 700 ppm.
Paper handling capacity - Laser printers support non-standard paper sizes, various paper types like transparencies, labels, card stock, even envelopes. Some models support additional paper trays, automatic document feeders, duplexers, staplers. Duplexers automatically turnover papers and allows printing on both sides. Xerox offers one model with private collator that keeps sensitive documents locked in bins that can be opened with only a password.
Printer languages - Page description languages are of two types - the Printer Control Language (PCL) and the other Postscript . PCL is the standard language for all HP and HP compatible printers. Printers used for printing letters, database printouts, spreadsheets and simple graphics require PCL. Those with desktop publishing software and drawing packages come with Postscript and these printers are comparatively more expensive. Laser printers with PCL can be upgraded to Postscript, provided the printers have enough memory to support it. The manufacturer provides the software driver for this up-gradation and it comes for an additional cost.