Why is LED technology better than laser? (and worse)
Terminology
Laser printing is the common name for a printing method using the principle of dry electrostatic transfer. The essence of the principle is that the coloring matter (toner) “sticks” to the photosensitive drum due to electrostatics in those places where it was exposed to a light source. Next, the toner is pulled onto the paper due to electrostatics, as a result of which an image is formed on the paper, which is fixed in the printer's oven under the influence of temperature and pressure.
Traditionally, a single laser diode is used as the light source, the beam from which, passing through the scanning system, enters the photosensitive drum. But the laser diode is not the only light source used in modern printers. A worthy and in many ways an interesting alternative to the laser are light emitting diodes (LED from Light Emmitting Diode) assembled in a line called LED Line. Both light sources make it possible to produce prints that are absolutely identical in terms of a set of consumer properties. However, each of the technologies has its own characteristics.
Consider LED printing in more detail.
Main advantages:
compactness and absence of moving parts;
no ozone emission;
high image accuracy
information security
high speed
Laser (top, cover removed) and LED (bottom) light sources for electrographic printers
LED ruler design: from top to bottom - a cover with focusing lenses, textolite board with LEDs and contact group, dielectric and metal housing
Separate LEDs for large magnification (LED line with a resolution of 600dpi)
Compactness and lack of moving parts
The light source in the LED printer is thousands (from 2,500 to 10,000 pieces) of individual LEDs mounted on a PCB in the same way that ordinary electronic components of modern devices are mounted. The PCB itself is placed in a metal case, which prevents its damage.
Thanks to the miniature size of the LEDs, they can be placed in a very small device - an LED line (also called a print head). The size of this head is so small that OKI LED page printers are still the most compact black and white printing devices in the world!
In the laser printer, however, a rather complex optical-mechanical system is used, in which there are mirrors with precision for adjustment and a rotating multifaceted prism (it makes an easy whistle when the laser printer is working). It is traditionally believed that a system that includes moving parts is less reliable than a system without such parts. This postulate is tested by time and in relation to OKI LED heads. Since 1999, they have been given a lifetime manufacturer's warranty!
There is no release of ozone.
Ozone - triatomic oxygen, which is a highly active chemical element (oxidizing agent). In small quantities, ozone is useful for the human body, but in large quantities it is very harmful, since it is a conditionally potent poison.
One of the common sources of ozone in everyday life is the copying and duplicating technique. In the design of such a technique there used to be an element called a coronator, which is a thin wire through which a high-voltage current passes. The oxygen in contact with this wire is ionized and ozone is produced from it.
In modern devices, the coronator was abandoned, replacing it with a special roller, which actually prevents the generation of ozone. But another source of ozone remained in laser printers - the laser beam itself. If you look at the diagram of the laser printing system, you can see that the laser beam makes a rather long journey through a system of mirrors and lenses before it reaches the surface of the drum. On this path, it electrifies the air, which is also accompanied by the release of ozone. Of course, not in the quantities in which the coronator produced it, but the characteristic smell of ozone is still felt during the operation of the laser printer.
This disadvantage is completely devoid of LED printers. The distance from the LEDs of the printing line to the surface of the drum is so small that there is practically nothing to ionize on this gap, and the characteristics of the light emitted from the LED lines are such that they cannot decompose oxygen with the release of ozone. That is why LED printers are the most environmentally friendly devices for modern toner printing.
High image accuracy
When a laser printer is operating, each line of the future image is formed when the laser beam “scans” the surface of the photosensitive drum (drum). The prism deflecting beam is rotated by a stepper motor. At each step, the prism rotates at the same angle. However, due to the fact that in order to reach the surface of the drum, the beam needs to go through different at the center of the drum and along its edges, the distance between adjacent points will differ. In addition, due to the fact that the beam falls on the edge of the drum at an angle to its surface, the very shape of the point that will be formed on the photodrum is not round, but oval.
In the LED printing system, a LED is located above each point of the drum. The distances between the diodes in the line are the same, and the shape of the point does not change along the length of the drum. It is these properties that provide equally high image accuracy both in the middle of the sheet and along its edges. And that is why professional printing systems do not use a laser scanning system, but work according to principles similar to those used in LED printing devices.
The differences in image accuracy described above can be seen with strong magnification of small text. For example, below are two fragments of text with a 1.5pt size, made by laser and LED printers and scanned with the same parameters:
Fingerprint made by a laser printer with a resolution of 1200x1200dpi. Pay attention to the quality of drawing small elements of letters - all the "circles" are filled with toner.
Fingerprint made by an LED printer with a resolution of 1200x600dpi. Even with the initially lower physical resolution, an LED printer handles the finer details of text much better.
Information Security.
The laser diode, which operates as a light source in a laser printer, emits a series of successive light pulses that reach the surface of the photoconductor and create an electrostatic image on it, which is subsequently converted to a print. However, like any other electronic device, a laser diode emits not only in its operating range (laser beam), but also in the radio range, being, in fact, a radio transmitter. Each dot, which is placed on paper, and from which the printed image is obtained, corresponds to one pulse in the air. Using modern technology, these pulses can be received on the radio antenna, sent to a computer and restored with the help of the image printed by the printer.
Light-emitting diodes in the LED printer also create electromagnetic waves that can be picked up by the receiver, but due to the fact that there are a lot of LEDs in the print line, and they all flash at the same time, there is “white noise” that cannot be decrypted (to determine which of the diodes “Flashed”, and which one didn’t, respectively, where the dot was placed on the paper and where not), that is, you cannot restore the image that is printed on the LED printer. Such security of documents printed on LED printers can be demanded in any critical places when printing secret and closed information, as well as where personal data about customers is printed. Indeed, according to the law on the protection of personal data, it does not matter how the leak of this data occurred, the responsibility under the law is always the same. Therefore, if you intend to print personal data on a laser printer, be prepared to become guilty of violating this law. So it’s better to immediately use LED printers to print such data!
High speed
Due to the fact that all the LEDs in the line are placed in one row and flash at the same time, the printing speed of LED printers is practically unlimited. In contrast, laser printers, which are forced to draw each line of the image sequentially, have physical limitations on the maximum print speed depending on the horizontal resolution used, which does not cause geometric distortion of the printed lines. The graph on the right clearly shows that with a physical resolution of 1200dpi, the maximum print speed of a laser printer is about 20 pages per minute. At a higher print speed, linear distortion of the print lines will occur: the lines will not be strictly horizontal, but slightly inclined. An alternative to distortion would be a reduction in physical resolution. For example, when printing with a resolution of 600dpi, the maximum speed of laser printers can reach 50 ppm. If it is necessary to achieve high speed with high resolution, designers are forced to install two or more laser mechanisms in laser printers, each of which will work only with a part of the image. This significantly increases the cost of the design and increases its dimensions, in addition, it creates obvious problems with setting up such printers. All these problems are fundamentally absent from LED printers, for which restrictions on print speed lie far beyond the actual print speeds. If it is necessary to achieve high speed with high resolution, designers are forced to install two or more laser mechanisms in laser printers, each of which will work only with a part of the image. This significantly increases the cost of the design and increases its dimensions, in addition, it creates obvious problems with setting up such printers. All these problems are fundamentally absent from LED printers, for which restrictions on print speed lie far beyond the actual print speeds. If it is necessary to achieve high speed with high resolution, designers are forced to install two or more laser mechanisms in laser printers, each of which will work only with a part of the image. This significantly increases the cost of the design and increases its dimensions, in addition, it creates obvious problems with setting up such printers. All these problems are fundamentally absent from LED printers, for which restrictions on print speed lie far beyond the actual print speeds.
Often highlighted flaws:
The resolution is not more than 600 dpi, and the images created by LED printers are often obtained with blurry and fuzzy edges, thin halftone lines had gaps, color matching on color images was inaccurate. Print quality, especially in terms of resolution and stability, is a weakness of LED printers.
Firstly, a big misconception about the resolution of "no more than 600dpi." Already in the 2000s, OKI released two older models of color printers - C7400 and C9400, formats A4 and A3, respectively, the resolution of the LED lines of which was 1200dpi. Then there were the C7500 (A4) and C9500 (A3) models, then the C9800 (A3) and, finally, today's C9850 in A3 format. All of them had 1200 separate LEDs on one inch of the LED line, due to which the physical resolution of 1200x1200dpi was achieved.
“Blurred and fuzzy edges” is completely a figment of imagination and speculation. For a very long time, LED printers have been using technology for smoothing vector images based on the ability of LED rulers to create dots of various sizes. Even the most inexpensive and, frankly, not the best representatives of the OKIPAGE family of black-and-white printers, gave more than enough smoothness for text and vector images already at a basic resolution of 300dpi! What can we say about today's printers, working with a resolution of 600 and 1200 dpi and fully utilizing the same technology!
But the image is not stable enough - a homespun truth. But ... 10 years ago. Indeed, 10 years ago, the LEDs in the lines slightly differed in the intensity of the glow from each other, which gave a slight banding along the movement of the sheet. But with the advent of the C7000 and C9000 series printers in 2000, they saw the light and new lines, the luminescence of each LED in which was automatically controlled and normalized to one level. Since then, the issues of image stability due to the difference in the glow of the LEDs have not been raised.
Conclusions
compactness and absence of moving parts.
Provides small size of the mechanism and long trouble-free operation of the device. The most important element - the LED line - is given a lifetime manufacturer's warranty!
no ozone emission
LED printers are the most environmentally friendly of modern toner printing devices, preventing the harmful effects of ozone such as dizziness and drowsiness.
high accuracy of the image
The created documents are distinguished by high accuracy and linearity of the image, technologically unattainable on classical laser printers.
information security
LED printers can be used in applications that require increased confidentiality of workflow.
high speed
In LED printers, you do not have to sacrifice speed or print quality, since flare parallel to the entire width of the sheet makes it possible to print without speed limits with any optical resolution, which is not available for laser printers.
Which does not apply to LED technology, but is attributed
Very often, when considering LED printers, people ask themselves a question - what happens if one LED burns out, how does a pixel burn out on a monitor screen? However, this rather funny question can in no way be attributed to LED technology. We need to look for an association in another area of computer technology and ask ourselves - what happens if one transistor on a processor burns out? After all, there are orders of magnitude more than the LEDs in the line, and the manufacture of both of them, by and large, is done using similar technological processes. And in both cases, the weak link is rejected at the production stage, and as the percentage of processors with faded transistors is extremely small, they almost never get into the printer and LED lines with faded diodes. If something happens to the LED bar, So this is a failure of the control board, responsible for a whole section of LEDs. Individual LEDs during operation fail so rarely that they do not even fall into the failure statistics, that is, they are outside the range of 0.01% of the total number of failures of LED printers. And in any case, no matter what happens with the LED line, we can always be sure that it will be replaced as part of a lifetime warranty! By the way: LEDs operate with an intensity of at least 5,000 times lower than the laser. Therefore, they do not fail. Therefore, such a guarantee. no matter what happens with the LED line, we can always be sure that it will be replaced as part of a lifetime warranty! By the way: LEDs operate with an intensity of at least 5,000 times lower than the laser. Therefore, they do not fail. Therefore, such a guarantee. no matter what happens with the LED line, we can always be sure that it will be replaced as part of a lifetime warranty! By the way: LEDs operate with an intensity of at least 5,000 times lower than the laser. Therefore, they do not fail. Therefore, such a guarantee.
OKI has been developing and improving its LED technology since 1987. Today, OKI is one of the few companies that continues to conduct fundamental technological research and independent developments in the field of black-and-white and color printing, investing significant funds in them. In this article, I only indirectly outlined the development directions for improving LED technology, however, as you can see, in recent years the technology has got rid of almost all of its shortcomings.
Sergey Lebedev OKI Marketing Director