High Bright Display Technologies & The Advantages
of VBOND
Large LCD displays for Dynamic Signage
• Retail digital signage is a great market.
• And now you want to take large LCDs outside.
• It should be easy, right?
Large LCD displays for Dynamic Signage
• New displays are 500 nits +• New displays are 2000+ : 1
contrast• They should be perfect, right?
What is a nit?
1 meter
1 meter
1 meter
A nit is a unit of projected light energy from one candle, measured from its source,measured one meter away, measured over a one meter square area. A footlambert is the same light measured one foot away, over a one foot square area. 1 ft lambert is the same as 3.426 nits
Contrast ratios: two methods, two results
350nits
Intrinsic Contrast RatioOn the surface, the display, may read a 300:1 contrast ratio. This does not take into account ambient lighting. In addition, the light meter is measuring total flux regardless of angular distribution
Extrinsic Contrast RatioA reading from a distance, taking into account ambient light and reflections. A good extrinsic contrast ratio is 10 :1.
How LCDs work
Liquid Crystal Display• Liquid = Fluid• Crystal = Organized Molecular Structure
When placed onto an alignment layer, the molecules will track in the general
direction of the grooves.
How LCDs work
Rear Polarizer
Alignment Layer
Cell Gap
Color filter on front glass
Front Polarizer
Transistors on rear glass
Light from the backlight is polarized and then twists 90 degrees through the LC material allowing it to
pass through the front polarizer.
How LCDs work
The transistor applies an electrical field across the cell. The LCD molecules align to the direction of the flow. This
prevents the LCD from twisting. No twist, no light transmission
Luminance vs. Illuminance
1000-1500 nits
1500 nits
• 1500 nits is read only on “white”
• Black level can go as high as 100-150 nits
• This is only 10-15:1 contrast
Effects of illuminance
1500 nits
10,000 ft Candles
5% reflection adds to the “white” level but also to the “black” level, lowering the contrast ratio, washing out the display
5% reflectionAmbient light is “illuminance”
Brightness versus Contrast
• “Brightness” lightens or darkens the image. “Contrast” changes the distinction between the light and dark areas.
• Humans can “perceive” roughly 100 levels of brightness.
• Humans can “see” roughly 1 billions levels of contrast.• The human eye eventually becomes saturated with
brightness and becomes more responsive to contrast. • Contrast ratio is much more significant than brightness
in high ambient illumination environments.• The human visual system amplifies the difference in
contrast: lateral inhibition
Contrast Example
This is a test
This is a test
High contrast, easy to read
Very low contrast but it is readable
Two types of display enhancements
Display enhancement has two approaches: Brightness and Contrast. Outdoor LCD displays require both in order to make them readable in high ambient light.
Brightness:• Active- Adding more lights • Passive- Collects and focuses the
available lightContrast: • Direct Bonding AR glass• Air gap AR film and windows
For outdoor viewability, one must increase both!
Passive Brightness Enhancement
50% of the backlight light never gets out the front
50% of the light will transmit in either of
these orientation
No light will get through at this
orientation
Reflective Polarizer
Passive Brightness Enhancement
Reflective Polarizer transmits all light in its orientation direction but will reflect back any light not in alignment. Additionally, the light is rotated slightly, to be reflected off the rear reflector.
Reflective Polarizer-
Passive Brightness Enhancements
Horizontally aligned BEF- Collects light going up or down
and channels it forward
BEF- Brightness Enhancement –
Vertically aligned BEF- Collects light going left and right and
directs it to the front
Passive Brightness Enhancements
Transflective Film- Mirror film
Light from the outside comes in, and is reflected off the rear wall
Passive Brightness Enhancement
ELG- Enhanced Light Guide
Light from the CCFLs is non-directed and bounces in all directions. Some light never makes out the front.
Passive Brightness Enhancement
ELG- Enhanced Light Guide
Micro-prisms internal to light guide
ELG with the Reflective Polarizer is very effective in converting non-collimated light to collimated light
Light returning from reflective polarizer
Light from CCFT
Active Brightness EnhancementDual tubes Multiple edge-lit
tubesMultiple rear-lit tubes
Contrast Enhancement with Anti-reflecting technology
Whether a film or glass bond, AR coatings eliminate reflective loss
Challenges of enhancing large LCDs
• DBEF- Factories already use it• BEFs- Steals light from the sides, not good• ELGs- Works with edge lighting, not rear
lighting.• Transflective film, hmmm maybe.• Backlighting- Displays already have high
bright back lights• AR film- Not big enough and very expensive
More challenges with large LCDs
• Large LCDs are designed for TV, with fast response and wide viewing angles.
• Their structure lowers light transmission from backlights by 50% (more lights, heat and power with lower results).
• Their fast responding LC material causes problems.
Challenges of enhancing large LCDs
• Have we mentioned HEAT?!?!?
Lots of heat from the CCFLs
50% of the heat load is Infrared radiation
Air gaps traps heat and allows it to go higher
Heat is a big issue
A display will go “isotropic” or
“clear” at as low as 50o C
Isotropic is the point where the LCD molecules go random (instead of organized, causing the
display to go black
Formulas
Luminance + ReflectionReflection
= Contrast Ratio
Reflection = 5% x # of surfaces x ambient light
Even with high bright backlights, contrast may be
low
Reflection = 10K ftC x 15% R= 1500 nits
5%5%
5%1500 + 1500
1500= 1.85 :1 Contrast
VBOND eliminates reflective loss and increases contrast
5%5%
5%
VBOND eliminates the two internal points of reflection. With AR coatings on the front, overall reflections drops to less than 2%
Reflection = 10K ftC x 2% R= 50 nits
1500*0.85 + 5050
= 26 :1 Contrast1500 nits
VBOND Benefits• Low reflective loss means higher
contrast in high bright environments• Display are daylight readable at 500 nits,
sunlight readable at 800 nits• Backlight power can be lowered to reduce
overall power draw and less heat production
• No air gap eliminates “greenhouse” effect heat rise. • Solid bond will conduct heat out of the
display• Cooler displays will not “clear”or go
isotropic as quickly.• No air gap prevents moisture from
forming under the window.
Benefits of VBOND for Outdoor Signage
• VBOND is not size dependent. Large size LCDs are no problem.
• Glass thicknesses and other features such as chemical strengthening or tempering is offered.
• Glass can be developed to reflect infrared radiation, lowering the heat load.
VBOND Benefits
• Reworkable through production process• Reworkable in post-production• Low toxicity, environmentally friendly
materials.• Excellent UV resistance• Excellent optical properties• Excellent mechanical properties• Low glass transition temperature