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
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
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
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.