Laser scanners usually take the form of the characteristic "gun" type shape, usually being trigger operated and apparently "firing" a slim beam of red laser light at the bar code. The beam effect is in fact an optical illusion. What is actually happening is that a pinpoint of laser light is being scanned across the code at a rate of around 30 scans per second, the speed and intensity of the scan creating the "line" effect. The very practical and useful result is that the user can see exactly where the laser is being targeted and "shoot" the scanner at the bar code correctly.

Laser scanners have two major benefits: firstly they generally have a much greater depth of field than CCD scanners, normally operating at around 15 to 20 cms from the bar code (although this can vary according to the code size). Some laser scanners are special long range versions that can operate even further away, but these usually use the much higher powered Class II lasers and are both more expensive and require higher power to drive them.

The second major benefit is that of speed and accuracy of reading. Because the laser is scanning the code at a high speed, it quickly has a lot of "goes" at reading the signal, hence the decoding will often appear to the user to be virtually instantaneous. As a double check the scanners are often set to have "redundant read" option which means that the scanner will not confirm and process the scan until it has received the same reading two or three times; only then will it be happy that the code has been correctly read. Redundant reading can be so fast with laser scanners that two or three times redundant scanning is often a default setting and many users will be completely unaware that this additional error checking is even happening!

The relatively low amounts of energy used in laser scanners do lead to limitations of use in conditions of high ambient light, for example outdoors in good daylight. In these cases the background light energy can be higher than the reflected light from the laser, effectively "dazzling" the scanner. For this reason laser scanners are generally not suitable for use outdoors, although specially designed outdoor models are available. CCDs and even wands can suffer from similar problems although usually to a lesser extent.

Laser scanners also exist in other forms apart from the familiar gun style. The next most common form is the fixed head laser scanner. Modern supermarket check-outs are generally equipped with fixed head scanners. Instead of the side to side scan of the laser gun, fixed scanners fire the laser beam in special patterns with the objective of intercepting and reading a passing bar code presented at any angle. The same approach is applied to the industrial use of fixed scanners where, for example, a scanner may be mounted to read codes on items passing along a production line.

Output signals from laser scanners generally take the same form as that of CCD scanners, i.e. decoded serial, wand emulation or keyboard wedge output. In addition some scanners transmit a raw laser signal (laser output) and must be attached to suitable decoding equipment. Specialist EPOS (electronic point of sale) terminals sometimes require an output type known as OCIA.

I thought laser beams were dangerous. Are laser scanners safe ?

The short answer is yes, in proper use they are quite safe. Certain international standards define the safety considerations for different power levels of laser light used in electronic products. The details are very technical, however class 1 lasers, the lowest power, are very low power. The level of light energy that the human eye would receive from a class 1 laser is (as a rough guide) less than the light it would receive on a bright sunny day! In any event, the normal human eye blink action would provide more than adequate protection if a class 1 laser should happen to hit it.

Class 2 lasers are higher power than class 1 and carry warning labels about the possible effects of looking directly into the laser beam. However, these products are still safe in general operation for two reasons: firstly the blink reaction will normally protect the eye in adequate time to avoid any damage; secondly, with bar code scanners, the beam is constantly moving. As a rough guide the intensity of a class 2 laser beam is roughly analogous to looking at the sun, thus users are strongly advised to avoid doing so!

I've been advised to buy a "medium resolution" reader. What does this mean ?

Resolution refers to the ability of a given scanner to "see" different sizes of bar code elements. If you have very small bar codes where the size of each element (i.e. the smallest bar) is very narrow, then you will need a reader capable of seeing very small bars. This requires a high resolution reader.

A larger bar code can of course be read with a high resolution reader. The main risk here is that larger codes can be more susceptible to imperfections that a high resolution scanner might detect. Hence a bigger or poorly printed bar code is often best read with a lower resolution reader.

For the vast majority of day-to-day applications, a medium resolution scanner represents the best compromise between these two extremes. Most users normally only have to concern themselves about resolution if reading very small or very large bar codes.

Resolution is normally expressed as the width that a given scanner can resolve down to: medium resolution is usually viewed as around 0.15mm - 0.19mm.