– We Engineer Light
VarTech Systems specializes in the manufacture
of high-brightness LCD display systems. Standard color LCDs
are often unable to provide sufficient luminance for viewing
under bright, outdoor environments; the result is poor image
quality. VarTech’s high brightness monitors deliver
a radically higher level of brightness, resulting in unparalleled
picture sharpness. Our high-performance products are ideal
for use under any high ambient light condition, and will give
you the intensity and brilliance your application requires.
products are commonly found throughout the following real
transportation systems (automotive, marine & avionics
- Industrial and medical systems
- Dynamic advertising (commercial advertising displays)
- Outdoor presentation systems (kiosks, drive-though ordering
- Sports facilities
- Military equipment
The display screen on a sunlight readable/outdoor
readable LCD should be bright enough so that the display is
visible under strong sunlight. Second, the display contrast
ratio must be maintained at 5 to 1 or higher.
Although a display with less than 500 nits
screen brightness and a mere 2 to 1 contrast ratio can be
read in outdoor environments, the quality of the display will
be extremely poor. At Landmark, a truly sunlight readable
display is typically considered to be an LCD with 1000 nits
or greater screen brightness with a contrast ratio greater
than 5 to 1. In outdoor environments under the shade, such
a display can provide an excellent image quality.
Luminance is the scientific term for “Photopic
Brightness” which specifies the visual brightness of
an object. In layman’s terminology, it is commonly referred
to as “brightness”. Luminance is specified in
candelas per square meter (Cd/m2) or nits. In the US, the
British unit Foot-lamberts (fL) is also frequently used. To
convert from fL to nits, multiply the number in fL by 3.426
(i.e. 1 fL = 3.426 nits).
Luminance is a major determinant of perceived
picture quality in an LCD. The importance of luminance is
enhanced by the fact that the human mind will react more positively
to brightly illuminated scenes and objects. Users are typically
more drawn to brighter displays that are more pleasing to
the eye and easier to read. In indoor environments, a standard
active-matrix LCD with a screen luminance around 250 nits
looks good. However, a sunlight readable LCD with a screen
luminance of 1,000 will look even more beautiful.
Contrast ratio is also a very important
factor. Contrast Ratio is the ratio of luminance between the
brightest “white” and the darkest “black”
that can be produced on a display. Contrast ratio is another
major determinant of perceived picture quality. If a picture
has high contrast ratior, you will judge it to be sharper
and the image significantly crisper than a picture with lower
contrast ratio. For example, a typical newspaper picture has
a contrast ratio of about 5 to 7, whereas a high quality magazine
picture has a contrast ratio that is greater than 15. Therefore,
the magazine picture will look better even if the resolution
is the same as that of the newspaper picture.
A typical AM LCD exhibits a contrast ratio
between 300 to 700 when measured in a dark room. However,
the contrast ratio on the same unit measured under ambient
illumination is drastically lowered due to surface reflection
(glare). For example, a standard 200 nit LCD measured in a
dark room has a 300 contrast ratio, but will have less than
a 2 contrast ratio under strong direct sunlight. This is due
to the fact that surface glare increases the luminance by
over 200 nits both on the “white” and the “black”
that are produced on the display screen. The result is that
the luminance of the white is slightly over 400 nits, and
the luminance of the black is over 200 nits. The contrast
ratio then becomes less than 2 and the picture quality is
VarTech’s sunlight readable LCDs with
1500 nits screen brightness will have a contrast ratio over
8 with the same amount of glare under the same strong sunlight,
making the picture quality on these units extremely good.
Uniformity is another important factor relating
to sunlight readability. Uniformity is the maintenance of
luminance from one display area to the next. Non-uniformity
can be viewed as a gradual shift in brightness from one area
to the next on the display, making the display inconsistent
and less pleasing to the eye. Most of the LCD manufactures
specify uniformity by measuring the screen luminance at 9
points on the display.
At VarTech Systems, uniformity is measured
Uniformity = (Lmax – Lmin)/ (Lmax
where Lmax (Lmin) is the maximum (minimum)
luminance measured with a 10 mm diameter meter aperture over
the LCD active area except the last 10 mm area from the edges.
VarTech’s CCFL-enhanced products consistently
maintain a uniformity level of better than 20%.
All LCD backlights powered by cold cathode
fluorescent lamps (CCFL) require inverters. An inverter is
an electronic circuit that transforms a DC voltage to an AC
voltage, which drives the CCFLs. VarTech’s CCFL-enhanced
systems are equipped with high-quality inverters.
The dimming range or dimming ratio of an
inverter specifies its capability of performing backlight
luminance adjustment. For inverters used in notebook computers
and LCD monitors, the backlight luminance can be adjusted
typically over a dimming range of less than 10:1. That is,
the luminance is adjusted from 100% down to about 10%.
For very high brightness backlights used
within VarTech’s CCFL-enhanced sunlight readable LCD
systems, the inverters must be able to provide a much wider
dimming range. Otherwise, the LCD screen will be too bright
during nighttime conditions. Therefore, our inverters provide
a typical dimming ratio of 200:1, meaning that the luminance
can be adjusted from 100% down to 0.5%.
Dimming capabilities are beneficial because
lowering the backlight luminance will result in a lengthening
of the backlight life. It also lowers the power consumption
and the related thermal management issues.
One must remember, however, that any CCFL-enhanced
high brightness backlight system will consume a significant
amount of power, thereby increasing the LCD temperature. The
brighter the backlight, the greater the thermal issue. Additionally,
if the LCD is used under sunlight, additional heat will be
generated as a result of sunlight exposure. Temperature issues
can be handled through proper thermal management design. Thermal
management information can be obtained through discussions
with one of our technical sales professionals.
If power consumption and/or thermal management
are of paramount importance for your project, perhaps our
technology would provide a better solution.