DISPLAY BRIGHTNESS & CONTRAST ENHANCEMENTS

As more and more flat panel displays find their way into outdoor applications, the need becomes far greater for them to not only be able to withstand severe temperature extremes (heat and cold) and solar radiation, but the display must also be readable when exposed to extreme optical conditions such as direct and indirect sunlight, glare and reflection.

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Most off-the-shelf displays are not properly equipped to handle all of these requirements. The traditional approach demands installation of value-add backlights to boost brightness and incorporation of thermal management solutions to dissipate the heat generated by the backlights.

Additionally, although transmissive panels are now available with a white luminance of more than 400 nits, they do not provide adequate brightness or contrast to be considered practical in high ambient lighting conditions or direct sunlight.

The Myth

It is a common myth that increasing a display’s backlight brightness alone will make it usable in high brightness environments (i.e., sunlight readable). The reality is that the increase in brightness is only a benefit if it does not adversely affect the contrast at the same time.

For example, imagine that a value-add backlight is used to increase the luminance of an OEM display that has a white luminance of 200 nits and a contrast ratio of 300:1 (black luminance of 0.66 nits) by ten-fold to a white luminance of 2,000 nits. While the display is unarguably brighter, the increased brightness will not be of much 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 integration issues such as power consumption and heat dissipation, must be considered as a collective when designing a display for true sunlight readability.

General Digital offers three types of sunlight readable solutions. The first is the traditional value-add backlight solution. The second approach is to provide a transflective display which incorporates a highly reflective backlight that reflects ambient light back out of the display. Our third offering, and generally the most efficient and cost-effective solution, is the GenFlective display, a hybrid of transflective and passive enhancements.

Value-Add Backlights

Traditionally, value-add backlights have a short life expectancy; bulbs generally have a brightness half-life of 20,000 hours, which means that the backlight will only be able to produce approximately half of its original brightness after 20,000 hours. Compared to this, current OEM backlights often are rated for 50,000 hours.

A typical 2,000 nit backlight for a 10.4″ display will require as much as 20 watts, while a 600 nit 20″ backlight uses greater than 60 watts. Because of this high power consumption, heat dissipation is of paramount importance. Integration of thermal management such as heat sinks, cooling fans, heat exchangers, heat pipes, etc. is necessary to maintain safe operating conditions.

Although most recent value-add backlight designs do not add significant depth to the OEM display, they typically require more space in the integrated enclosure due to the necessity to provide thermal management.

By themselves, value-add backlights can be quite costly. In addition to the expense of the backlights and their associated electronics and packaging, most displays also require some optical films as well. When considering the integration of a value-add backlight, one must also consider the expense of the thermal management solution (typically required) as well as the increased cost of ownership resulting from shortened lamp life. And don’t forget about the special inverter(s) required to drive the backlights.

Transflective Panels

Although they are designed to reflect ambient light back out the display to augment its performance in direct sunlight, transflective panels have insufficient transmissive luminance (typically ~200 nits) to be considered usable in diffuse lighting conditions where direct sunlight is not available (e.g., cloudy or rainy days).

Additionally, transflective panels are only available in a limited range of display sizes and resolutions.

GenFlective Technology

A GenFlective-enhanced display is one that General Digital has altered, using passive enhancements, to improve the brightness (transmissive and/or reflective) and/or the contrast of the display. Although each display has its own personality, due to differences in design, manufacturing techniques and in the stock film stack, General Digital can typically enhance the performance of an OEM panel utilizing Optical Management Films, Polarizers and Diffusers, and a multitude of films and coatings (Contrast Enhancement, Index Matched, Antireflective, etc.).

In contrast to value-add backlights, displays enhanced with GenFlective technology do not require any additional power since General Digital has not modified the OEM bulbs, backlights or LEDs. In addition to reduced power consumption, this benefits the end user with cooler running units, which in turn negates the need for bulky, complex and/or expensive cooling systems (fans, heat exchangers, heat pipes, etc.) that traditional value-add backlights typically require. Another benefit resulting from these factors is improved reliability (reduced piece count).

Since the display’s lamps are not being overdriven, the GenFlective 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.

In theory, candidate displays for GenFlective enhancement can be of any size, resolution or manufacturing origin. The success of the candidate display is most influenced by the display’s aperture, transmissivity and the “personality” (OEM film recipe).

Combining GenFlective with Other Technologies

To further enhance LCD performance and improve its ruggedness, GenFlective technology can be combined with optical bonding, provided by General Digital’s Optical Bonding Laboratories.

Optical bonding of an LCD reduces internal reflection and increases brightness and contrast by index matching internal surfaces. It also creates a shatterproof construction similar to the properties of automotive windshields. An additional benefit is the optical-friendly integration of other options, such as heaters, EMI filters, hot mirrors (IR filters) and more.

Another combination utilizes low power active enhancement, which allows overdriving of cold cathode fluorescent tubes and multiple tube edgelight replacements.

Overdriving the bulbs, or using a drive current that is greater than recommended by the OEM manufacturer, will increase display brightness but will also reduce the brightness half-life expectancy of the bulbs. Increasing the number of bulbs will also increase the luminosity of the panel and add less than 10 watts of additional power consumption.

In some instances, GenFlective technology can also be combined with traditional value-add backlights for a “best of both worlds” solution.

Integration Decisions and Influences

To optimize the benefits and performance of the GenFlective-enhanced display panels, General Digital recommends that an index-matched-to-air antireflective coating be included on the outer viewing surface to improve contrast. Customers should note that special handling and cleaning instructions are required for the care of antireflective coatings.

Introduction of overlays that adversely affect light transmission, such as vandal shields, touch screens, EMI filters, hot mirrors, etc., will diminish the performance of the Genflective-enhanced flat panel display.

Overview

Light emitting displays all suffer from a visibility problem when used under conditions which include high ambient lighting levels. A common condition is exposure to uncontrollable outdoor lighting, such as kiosks, advertising displays, control towers and aircraft cockpits, to name just a few. The solution is to increase the luminance of the display well above normal levels expected for indoor use. The display contrast must be increased to maximum, as well. Because of these measures, precautions must be taken to avoid direct specular reflections from the display surface.

Several technologies have been developed to improve the situation. One of these technologies is film lamination. General Digital Optical Bonding Laboratories can passively enhance a display by applying optical films to its front surface, thereby improving brightness and contrast by reducing surface reflections.

General Digital Optical Bonding Laboratories is a National Distributor of Tigold Films (formerly known as OCLI). We also integrate films from other third party film manufacturers.

Antireflective Film (AR)

• Laminated to the front surface of the LCD panel. Can be performed either directly in-the-frame or under-the-frame. General Digital prefers the under-the-frame method to reduce risks of delamination.
• Reduces surface reflections, thereby improving brightness and contrast two to three times without actually making display brighter.

Antireflective Film and Antiglare Film (AR)

• Laminated to the front surface of the LCD panel. Can be performed either directly in-the-frame or under-the-frame. General Digital prefers the under-the-frame method to reduce risks of delamination.
• Reduces surface reflections, thereby improving brightness and contrast two to three times without actually making display brighter. Softens direct light source images in reflection.

Conductive Films (EMI/RFI Reduction)

• Laminated to the front surface of the panel. Can be performed either directly in-the-frame or under-the-frame. General Digital prefers the under-the-frame method to reduce risks of delamination.
• Reduces EMI emissions.

Specialty Films

• Reduces reflected ambient light more than the emitted light, thereby increasing contrast of the display.

Color Selective Films

• Alters the output color of the screen. Can be used to trim the output for special applications.

For further information regarding optical film enhancements or to request a quote for your application, please contact one of our qualified Sales Engineers.

Many Display Sizes Available

In response to customer demand, General Digital has engineered a multitude of sunlight readable and daylight readable LCD display solutions that feature OEM LCD displays and our custom-designed LED backlights (edge-lit and direct-lit), light optimization films and overlay enhancements. Our standard LCD display solutions range in size from 6.5 inch to 24.0 inch. New flat panel display sizes and resolutions, and subsequently, complete LCD monitor models, are being added regularly, or can be engineered upon customer request. Many of our sunlight and daylight readable display solutions also provide night vision goggle compatibility, as well.

Component or Monitor

Our enhanced display solutions may be purchased “off the shelf” for integration into your own product designs, or you may opt to have General Digital technicians expertly integrate the display of your choice into almost any of our monitor and display kit products. In addition, we can design and integrate the sunlight/daylight readable displays into a custom solution to meet customer-supplied design and performance requirements.

LED Backlight Advantages

• Greater efficiency (brightness vs. power)
• Lower cost
• More durable solid-state design
• Extended operating and storage temperatures
• No mercury content
• Faster startup times

Why are General Digital LED Backlights Necessary?

If LCD manufacturers are already manufacturing their LCD displays with LED backlights, you may wonder why General Digital produces its own value-add LED backlights. Most LCD manufacturers target large-volume markets for their LCD designs, where they can maximize their return on investment (ROI). Since competitive pressures from other suppliers exist in these markets, their products are designed to meet the bare essential requirements at a minimum cost in an attempt to achieve product acceptance and market competitiveness.

Traditionally, Original Equipment Manufacturers (OEMs) of liquid crystal displays have underserved niche markets (e.g., military, avionics, marine, outdoor usage) that require very specialized display performance, such as extended operating temperatures, sunlight readability, night vision capability and long product life cycle. General Digital prides itself on solving industry problems and providing product solutions to these underserved and specialty markets. Customers find our LED backlights to be necessary to meet one or more of the following application requirements:

• To provide superior brightness performance for use in high ambient lighting conditions or direct sunlight.
• To convert a legacy LCD design (that meets a specific need) from a CCFL backlight to a comparable design using less power, with increased durability and efficiency.
• To provide an LED backlight with greater reliability than the OEM design. Many OEM backlights have a Mean Time Between Failure (MTBF) between 30,000 and 70,000 hours. Typically, General Digital uses LEDs that have a have brightness rating in excess of 110,000 hours MTBF.
• To provide a more efficient LED backlight design than the OEM LED backlight that provides customer-required performance at lower power consumption/heat dissipation. This requirement is especially important for display solutions that are housed in fanless or fully sealed enclosures.
• To provide night vision (NVIS) goggle compatibility.
• To provide, in combination with our LED controllers, a wider dimming range than the OEM LED backlight/controller, as well as additional programmable functionality.

What Makes a Display Sunlight Readable?

There are many display performance attributes that must be considered when selecting a display to be used in high ambient lighting conditions or in direct sunlight, such as:

• Brightness
• Contrast
• Dimming range
• Viewing angle
• Operating life
• Power consumption
• Heat dissipation
• Reflectivity
• Response time
• Operating/storage temperature

OEMs provide the contrast performance of their LCDs in dark room conditions within their display specifications. While this information is an important indicator for consideration if the LCD is to be used indoors, it provides an inconclusive indication of how well the LCD will perform when exposed to high ambient lighting conditions (read our white paper, Not All Brightness is Created Equal). For this reason, General Digital quantifies the performance of our LED enhanced LCDs in our Optics Laboratory following the guidelines of MIL-STD-3009 (formerly MIL-L-85762-A).

Often, users prequalify panels by how bright they are, employing the “if it is brighter, it must be better” mentality. While brightness may indeed be an important performance consideration for many applications, General Digital holds that the display’s contrast is even more important. Ultimately, it is the user’s ability to discern a difference between colors (contrast) that enables them to properly view information under varying lighting conditions—from total darkness to direct sunlight.

Following these guidelines, General Digital provides our customers with a host of performance metrics, most notably its Weber Contrast, its contrast under 10,000 foot candles of direct light and a Display Class. These metrics allow customers to compare our performance to the military’s standard of approval for display usefulness in direct sunlight, as well as the type of information that can be read under these conditions, ranging from numeric-only to live video. This data also will allow customers to compare our products to competitive alternatives on a level playing field.

General Digital’s Optical Laboratory

General Digital’s Optical Laboratory was created to provide quantification of the optical performance of an LCD under a variety of extreme ambient conditions along with raw intrinsic system characteristics. The data provided by the laboratory tests allows for numerical performance descriptions of each LCD display system. This enables the customer to compare displays across the entire General Digital display catalog and provide the ability to choose the correct product for the target environment while removing guesswork. To ensure accuracy and cross correlation, sunlight and NVIS measurements adhere to procedures and regulations outlined in MIL-L-85762A, and its successor, MIL-STD-3009.

Enhanced LED Display Measurements

Typically, General Digital attempts to standardize its measurements by applying an antireflective film to the surface of the LCD. However, it is not unusual for us to test the displays using a variety of other combinations of overlays (EMI filters, touch screens, vandal shields or films) that may be required to meet a specific application requirement.

Lastly, we maintain a record of the data that summarizes and compares the optical performance of the OEM LCD before our enhancements and improvements, as well as after modification. Much of this data has been acquired under the guidelines of MIL-STD-3009.

The following is a standard list of carefully chosen measurements performed by General Digital’s Optical laboratory that provide all relevant information on dark/night, direct sunlight, ambient sunlight and night vision conditions.

Sunlight Readings

For more details, reference the documentation at the bottom of this page.

• Dark Room Data
  • Luminance A (Nits)
    • Measured in a dark room at optimal display brightness and contrast providing real world data. This data is provided for real world performance information.
  • Luminance B (Nits)
    • Measured in a dark room at maximum display brightness and contrast, providing maximum brightness; however, display readability is reduced through loss of contrast. This metric is provided for inter-vendor comparisons.
  • Contrast Ratio
    • Contrast ratio of the display in a dark environment.
• Sunlight Condition MIL-STD-3009
  • Weber Contrast
    • Weber contrast (as defined by MIL-L-85762A) of the display under full diffuser and specular simulation. This simulates an outdoor bright sun condition (10,000 fc) with a secondary reflection of the sun (2,000 fL) off the monitor system.
  • Contrast Ratio
    • Contrast ratio of the display under full diffuse and specular simulation sources. This simulates an outdoor bright sun condition (10,000 fc) with a secondary reflection of the sun (2,000 fL) off the monitor system.
  • Direct Sunlight Only Contrast
    • Contrast ratio of the display under diffuse simulation source ONLY. This simulates an outdoor bright sun condition (10,000 fc).
  • Display Class (0-6)
    • Classification of the display usability, 0 being not sunlight readable with text, image or video, black and white or otherwise, and 6 being readable given full color motion video.
• LED Backlight Data
  • Rail Temperature °C
    • Temperature of the backlight illumination source in each drive condition.
  •  Watts
    • Power being consumed by the backlighting system in each drive condition.
  • LED MTBF (Hours)
    • Mean time before failure of the backlight system, this will change depending on type, vendor and model of illumination source.
• NVIS (MIL-STD-3009)
  • U’V’
    • Color coordinates in the CIE 1976 (L’,u’,v’) color space of the display in NVIS mode (if equipped).
  • Error Radius
    • The radial deviation distance from the MIL-STD-3009 defined NVIS B CIE 1976 NVIS B white point.
  • NVIS Radiance B
    • The NVIS B radiance in nw/cm²/sr.

Drive Options

• OEM Performance
  • Driven with the OEM or General Digital LED backlights at a power equal to the OEM backlights. This provides data on luminance improvements over OEM if equipped with our backlights.
• OEM Brightness
  • Driven with the OEM or General Digital LED backlights to produce brightness equal to the OEM display brightness. This provides data on power consumption improvements over OEM if equipped with our backlights.
• 1000 Nits
  • Driven with the OEM (if possible) or General Digital LED backlights to produce 1000 nits. This luminance is chosen as it is an industry recognized number for sunlight readability; however, the importance of contrast over brightness for sunlight readability must be emphasized. 
• 50°C Rail Temperature
  • Driven with General Digital LED backlights to determine the maximum output of the display with no active cooling. Many displays can be pushed beyond this threshold; however, active cooling or heat sinks may be required.

The metrics outlined above represent most common conditions; however, due to General Digital’s vast array of capabilities, experience and equipment, many more display measurements can be obtained. Should further assistance be necessary, a Sales Engineer can be consulted for additional clarification.

LED Backlight Controllers

General Digital also designs and integrates our own line of intelligent LED backlight controllers to provide command, control and status of our  NVIS-enhanced and NVIS/Sunlight Readable-enhanced displays and backlights. Again, these ruggedized products can be purchased from our stock or integrated by General Digital. Additionally, our software engineering staff can tailor our controller firmware to provide the precise performance necessary to meet a customer’s operational requirements. Typical requests include, but are not limited to, the following:

• Minimum and maximum brightness levels for NVIS luminance.
• Minimum and maximum brightness levels for standard/sunlight readable luminance.
• Brightness resolution (number of brightness steps between minimum and maximum set points).
• Automatic brightness control algorithm adjustment based on ambient lighting conditions.

Other Controllers

General Digital also designs and assembles standard and custom microelectronic assemblies in house (e.g., embedded display heaters, cooling fans, touch screens, bezel buttons and potentiometers, OSD controls) that may be included in the final configuration. Since these designs are under our control, it is a simple task for us to program or tailor their performance to meet a variety of needs. More information is available by speaking with a Sales Engineer.