As
an increasing number of LCD flat panel displays
(both commercial grade as well as more ‘ruggedized’
units) find their way into outdoor applications,
the demand becomes significantly larger for these
products to not only be able to withstand wider
temperature extremes (cold and hot), but the viewable
images from these displays must also be readable
when exposed to extreme optical conditions such
as direct sunlight and/or high ambient lighting
condition, especially where glare and reflection
are most common and subsequently create undesirable
imaging results.
The
majority of commercial displays are not properly
designed to address these demanding requirements.
A very common approach by many LCD product manufacturers
is to simply integrate higher wattage CCFL or
LED backlights to increase brightness of the display
image. This approach and way of thinking has a
multitude of flawed aspects…one being ‘heat’.
The more wattage one integrates to merely boost
luminance, the greater the need for complex thermal
dissipation. There are even instances where these
manufacturers incorporate no additional thermal
management solutions to dissipate the heat generated
by the enhanced backlights. Heat, regardless of
backlight type (CCFL or LED), will significantly
shorten the life expectancy of not only the backlights
themselves, but as well many other internal electronics
and optical materials. Consider further reading
our whitepaper article LCD Operating Temperatures
where we discuss “Going Isotropic”.
On
the opposite spectrum of things, some LCD product
manufacturers are integrating “transmissive” enhancements
only and, although many panels today are offered
with higher “white” luminance of more than 400
cd/m2 (nits), these products do not adequately
provide enough brightness and/or contrast improvements
to be considered practical in high ambient lighting
conditions and certainly not in direct sunlight.
The
Myth
A common myth is that simply increasing a display’s
backlight brightness alone will make it readable
in direct sunlight or other high brightness environments.
The reality is that merely boosting levels of
brightness is only a benefit if it does not adversely
affect the contrast of the display image at the
same time.
A
distinct characteristic of human vision is contrast
or the difference in visual properties that makes
an object (or its representation in an image)
distinguishable from other objects and the background.
In visual perception of the real world, contrast
is determined by the difference in the color and
brightness of the object and other objects within
the same field of view. Because the human visual
system is more sensitive to contrast than absolute
luminance, we can perceive the world similarly
regardless of the huge changes in illumination
over the day or from place to place. Subsequently,
it is for this very reason that contrast plays
the biggest role in viewing images in direct sunlight
or high ambient light conditions. Luminance is
only a small factor. Try this exercise….as the
contrast level
decreases images
become less
visible even though the background
brightness remains the same. The human eye significantly
notices contrast changes, so simply making an
LCD display brighter does not necessarily make
it visually appear better nor easier to view in
direct sunlight. One can increase the luminance
of a display to the point of greatly reduced contrast
and thus progressively diminishing image visibility.
For
example, let’s consider that an LCD product manufacturer
enhances the backlights to increase the luminance
of a particular display that has a white luminance
of 200 cd/m2 (nits) and a contrast ratio of 300:1
(black luminance of 0.66 nits). This hypothetical
manufacturer boosts the backlights by ten-fold
to a white luminance of 2,000 nits. While the
display luminance output is without argument considerably
brighter, the increased brightness will be of
little or no actual value in direct sunlight if
the “black luminance” is correspondingly increased
from 0.66 nits to 660 nits (contrast ratio of
3.03). These factors, as well as other now inherent
integration issues such as increased power consumption
and the need now for complex thermal ‘heat’ dissipation,
must now be considered as a collective when designing
a display for true sunlight readability. Not to
mention, that if optical bonding of the LCDs frontal
protective window or touch screen isn’t added,
reflection still exists. More on this can be learned
from reading our article titled Optical
Bonding.
For
many of its products, VarTech Systems integrates
a number of active and passive enhancements to
its ‘sunlight readable’ solutions. The first is
the integration of traditional value-add backlights
to increase the luminance of the display well
above normal levels expected for indoor use. The
display contrast must, however, as well be increased.
Because of these measures, precautions must be
taken to avoid direct specular reflections from
the display surface.
The
second is to incorporate VBOND, a unique optical
bonding technology which combines an innovative
bonding process with an industry-leading proprietary
adhesive to optically bond an anti-reflective
glass, plastic or touch sensor directly to the
front of an LCD display. VarTech’s bonding technology
enhances display performance by improving sunlight
readability up to 400% and impact and scratch
resistance up to 300%. It is ideal for use in
consumer and industrial applications requiring
outdoor viewability and the durability to withstand
impact, vibration, extreme temperatures, altitudes
and dust.
But
the third modification is to integrate an innovative
optical stack enhancement (OSE), a unique optical
design which boosts efficiency of the backlight's
light utilization and minimizes the surface reflection
of ambient light. The result is a transmissive
enhancement that features higher contrast and
a wider range of colors, even in bright outdoor
light, than traditional reflective LCDs. This
is accomplished by:
Recycling
what would be wasted off axis light and then redirecting
light towards the viewer;
Reflecting
and recycling polarized light which under normal
circumstances 50% of the backlight output would
have been absorbed into the LCD and subsequently
wasted;
Finally,
the use of a multilayer, ultra-high reflectivity,
mirror-like optical enhancement film that is used
as a very efficient light guide and cavity reflector
with a reflectivity of 98.5% across the visible
spectrum which provides a brighter more efficient
display.
And
while VarTech does add increased backlighting
to its sunlight readable products, the integration
of theses innovative films to the LCDs optical
stack allow for much lower wattage value-added
backlights to be needed. So, in contrast to those
companies who are simply adding significantly
higher wattage value-add backlights to its products,
displays enhanced with VarTech’s unique technology
do not require huge amounts of additional power.
This benefits the end-user with cooler running
units.
Since
the display’s lamps are not being overdriven,
the VarTech enhancements do not adversely affect
the brightness half-life of the bulbs. A direct
correlation exists between the brightness half-life
of the bulbs and the suitability and cost of ownership
of the integrated solution. For example, most
bulbs are rated for 50,000 hours when operated
at their intended drive current. As a rule of
thumb, the bulbs will lose 10% of their initial
brightness during their first 500-2,000 hours
and 1-5% for every 1,000 hours of use thereafter.
Longer brightness half-life also reduces the cost
of ownership by reducing the frequency in which
the backlights must be replaced.
Those
models which VarTech incorporates its unique Optical
Stack Enhancement (OSE) technology are typically
combined with its optical bonding process as well.
This process (VBOND, as mentioned above) produces
an optical bond between any display cover glass
or touch panel, and any size LCD.
Utilizing
advanced proprietary optical bonding technology;
VarTech Systems overcomes optical challenges for
display product manufacturers at an affordable
price. In a wide range of applications, standard
liquid crystal displays appear to "washed out"
in high ambient lighting conditions. This wash
out is due to excessive reflections and glare
caused by bright light. Commercially available
LCDs, especially when protected by a separate
cover glass or plastic shield, can not deliver
enough brightness to make the display functional
in outdoors or in other high ambient light applications.
The exclusive VBOND process provides a significant
reduction of ambient light reflections at an affordable
price, compared to other display enhancement technologies.
VBOND
seals either a top cover glass or touch screen
directly to the face of the display bezel. Our
bonding process eliminates the air-gap between
the display and the cover glass, vastly reducing
reflective light, which causes visual washout
of the display image. VBOND also enhances structural
integrity by supporting the LCD assembly with
the cover glass. The bond maintains perfect display
uniformity while providing shock protection, unlimited
humidity protection, and elimination of fogging
caused by trapped moisture accumulating in typical
air-gap assemblies.
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