Tuesday, September 4, 2012

Rugged Displays

There are about 3 dozen parameters by which you can measure a display. Occasionally there is either a technical breakthrough or someone opts to up the performance on one of these significantly beyond the norm and then promote that feature heavily. Other device makers then follow suit to capitalize on the promotional spending the first mover is making with their own performance improvements and promotional spending. Soon performance and the claims of performance move beyond what the average person can actually experience, beyond what anyone can see, and sometimes beyond what can even be measured on conventional equipment.

Lately these have tended to focus on electronic improvements due to the funding sources for R&D in the industry. A prominent computing company frequently they surveys users of computing devices and regularly finds that ruggedness was always in the top three of areas where consumers desire improved performance. However increased ruggedness involves making trade-offs from areas the company was pushing, specifically thinness. So this is not an area that gets much attention from the company or its competitors even though it has very high consumer utility. In the notebook area, I am only aware of Panasonic with their Toughbook brand, actively promoting ruggedness. In the cell phone are, in-spite of designers desire to make cell phones increasingly thin, we find out from of the out-fall of the Apple v. Samsung case that the vast majority of cell phone user encase their phones, sometimes doubling or tripling the thickness in order to increase the ruggedness.

Of course, there are also companies that specifically make devices for children that necessarily design to more stringent specs; but toughness has not widely caught on within the industry… with a few exceptions that are mostly prescriptive. The ThinkPad has a special rubberized paint that gives it better impact performance. The iPhone has the Gorilla Glass cover instead of a plastic one to give it better resistance against surface scratches (keys) in your pocket. Sony also has offered a TV set with a Gorilla Glass cover to prevent screen damage in case the kids get too involved in their video games. However, there are other challenges besides impact and surface scratches.

Early smart phones were very susceptible to moisture. Rather than fix the problem, the first reaction was to mark them with a dye that changed color when it got wet. This relieved the maker from having to pay for replacement of wet phones but did not solve the consumer’s problem. Lately, cell phone case makers have been offering water resistant models and some cell phone makers have introduced product that can actually be submerged without damage. In larger LCDs, digital signage and outdoor LCD TV sets have developed encasements that allow these devices to operate in the rain.

The sun can impact performance of a cell phone or mobile device in two ways. First, trying to use your mobile device outdoors is frequently problematic as the sun washes out the screen. Although this is not specifically ruggedness in that it is not a permanent failure of the device, it does render the device useless. The wash out can be so thorough, that it is sometimes not apparent that the screen is on. Pixel Qi makes a screen that is viewable in direct sunlight; I had expected that type of screen to star appearing on mobile devices before now. There is also a rumor that one of the next Kindles will have both an LCD and an e-paper display.

A second impact of the sun is radiant heating. The unsourced diagram shows the heating of the dashboard of a BMW on a 100 degree July day. The upper (green line) shows the dashboard reaches 185 degrees while the ambient (lower blue line) gradually climbs to 100. Please note that although the ambient air in the interior of the car may reach 145 degrees, the dashboard temperature is more a direct result of the amount of solar radiation it is receiving and the temperature curve reflects the rapid increase in radiation rather than the gradual increase in ambient temperature either inside or outside of the car. Further the dashboard is protected from some of the solar radiation by the glass in the car. An object in direct sun, say left on a picnic table near the summer solstice can reach 210 degrees or more and that equilibration with the current level of solar radiaon can happen in only about 10 minutes. Other than Apple’s preference for white encasements, little has been done to isolate mobile LCDs from possible impairment by the sun.

This may change. Although optical isolation is not a focus issue with mobile devices, it is a recognized problem with digital signage where both ambient light wash out and solar thermal clearing are substantial problems. Currently, the digital signage world basically lives with image wash out and uses active air cooling to combat the thermal issue. One LCD maker also seems to have a product that is significantly more temperature resistant to thermal clearing; however, I do not see them promoting this. More sophisticated approaches are available and the signage industry is actively investigating these. As they are applied to digital signage, they might also find their way into mobile devices as well.


  1. Other than breakage, two of the most common defects on an LCD in the consumer's hands are scratches to the polarizer and a defect sometimes called mura. A Gorilla Glass cover was implemented on smart phones because scratched polarizers, already common on notebooks, gets worse with a phone in someone's pocket with their keys... per the Steve Jobs biography.

    Mura was originally a LCD manufacturing defect, where having the spacer not quite right resulted in dark patches on the screen. In current times, it gets applied to almost any brightness variation, a common one being thermal damage to the polarizer. Both defects can be repaired by replacing the polarizer.

    As the defect rate of scratched polarizers falls with widening use of cover glass, I expect the relative impact of mura will rise and optical isolation will get more attention.

  2. There are some comments on iPhone damage here http://techcrunch.com/2012/09/18/squaretrade-americans-have-spent-nearly-6b-on-iphone-repair-and-replacement-since-2007/


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