Overview

Many applications of displays involve installation in environments having a high humidity level. Of specific importance in this regard is the marine environment. In this application, an LCD, OLED or Plasma monitor, no matter how well sealed, will eventually “inhale” moisture within the enclosure. Once inside the enclosure, it is extremely difficult to remove the water vapor. As a result, the protective clear window installed in front of the display will develop a fogged appearance when it becomes chilled. Ways in which it can become chilled include direct impingement of air conditioned air onto the face of the display or spray impacting the outside. The fog which develops inside of the window is frequently difficult to remove without heating the glass or opening the display. General Digital™ Optical Bonding Laboratories™ has developed two distinctly different ways to prevent this from being an issue.

The first technique is to optically bond the window to the flat panel display. This eliminates the air space between the display and the window, thereby eliminating moisture entirely from the space, and hence, the problem of condensation.

The second technique it to provide a hermetically sealed window which includes a desiccating gasket as a part of the seal. This window is, in effect, a custom thermo-pane window tailored to the display. The following paragraphs will describe in more detail the trade-offs in this design.

Basic Design

Two pieces of glass are held in close proximity to one another and are sealed by a specially designed gasket. This gasket, in addition to providing a spacer for the protective window also excludes interchange with the ambient air. The adhesive used is designed to provide a moisture absorbing (desiccating) ability. Thus, as time goes on, the moisture content between the two pieces of glass will actually decrease. In addition, the dead air space between the two glass surfaces forms a thermal barrier, preventing the inner glass from becoming chilled when the outer surface is chilled. The overall effect is to eliminate the fogging which otherwise could occur.

Both our experience and the information from manufacturers of similar products show that the moisture content of a desiccant sealed optical window remains below 10% RH for years. Consequently, in the absence of mechanical damage to the protective window, the display will never be subject to condensation fogging.

Comparing the mechanical design of the sealed window to other designs, we find that this approach adds depth to the display. The thinnest design we would recommend is 7/16″. This is composed of two pieces of 3 mm glass, spaced apart by the thinnest desiccant gasket available (3/16″). In addition, there will need to be a small air gap between the inner layer of the window and the LCD, OLED or Plasma display. Compared with a 3 mm protective window, we need an additional 5/16″ inch in the display depth. Optical bonding does not add this extra space.

Flat Panel Displays find their way into almost every industry and all possible applications. As designers leap to take advantage of this technology and design them into products that range from iPods to Mega Digital Signage screens, it becomes inevitable that the off the shelf (OTS) LCDs require modifications. Modifications for sun light view ability, vandal shield, ruggedization etc. One such modification is the need for shield from Electromagnetic Interference. It is important to understand that the need for EMI shielding is not due to the LCD but due to the components in the overall product incorporating the Display emitting radiation. Hence, the need for shielding which can be integrated to the Display.

 As the demand for Displays rise, so is the need for Touch Screens that are integrated with the Display for ease of user interface. Display integrated with Touch enables the designer the flexibility of using the integrated unit to have the ability to also shield from EMI. Further, more and more applications demand the need for sunlight readable Display systems. In cases where such systems also incorporate Touch Screens, it becomes the designer’s delight as the Touch Screen can potentailly be used to achieve both optical enhancements and EMI shielding.

Please read attachment for detailed discussion.

emi-article

Posted By Vignesh Sanmugam

Overview

As more and more LCDs 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 LCD must also be readable when exposed to extreme optical conditions such as direct and indirect sunlight, glare and reflection. On an average sunny day, the illumination of ambient daylight is approximately 30,000 nits. Therefore, a TFT’s brightness should be over 900 nits to get a clear image for an outdoor application.

Most off-the-shelf LCDs are not properly equipped to handle all of these requirements. There are  several brightness enhancement solutions to meet/exceed our customers’ requirements.

Benefits of Brightness Enhancements for TFT Modules

• Increase brightness up to 100% with enhancement films alone
• Improve display contrast and readability
• Improve display clarity and image quality
• Superior uniformity
• Improved operating temperature range and brightness

Options

Both passive and active backlight modifications can dramatically improve sunlight readability. One of the most efficient and cost-effective solutions is the GenFlective™ display, a hybrid of transflective and passive enhancements. Avnet also offers a standard transflective display, which incorporates a highly reflective polarizer that reflects ambient light back out of the display. Thirdly, Avnet provides the traditional value-add backlight solution, an active enhancement featuring your choice of CCFL, LED or NVIS backlight technology.

Passive Enhancements

Benefits of GenFlective™ Technology

• Requires no more power than OEM panel
• Dissipates no more heat than OEM panel
• Simplifies integration of value-add display
• Easier to address cooling due to low power
• Can often be combined with other passive enhancements (optical bonding) or active enhancements (sunlight/daylight readable backlights/edgelights)
• Typical enhancement of OEM luminance of 20% to 100%

A GenFlective™-enhanced LCD is a display that has been 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, our value-add partner 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.)The display would be characterized under darkroom conditions and three different simulated daylight conditions. We would then do an evaluation of the OEM films in the LCD and modify this configuration as we deem reasonable. We will do up to four iterations of backlight film modifications and submit the data to you, along with our analysis of what the data tells us. 

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 diffused lighting conditions where direct sunlight is not available (e.g., cloudy or rainy days).