Unbundling the Optical Stack for Better Environmental Performance

LCDs used outdoors as digital signage must be protected from the environment. Typically, they will have a cover glass to protect them from being poked and prodded. They may also have air-conditioning to protect the LCD from reaching its thermal clearing temperature or otherwise suffering thermal damage. Objects in direct sun can reach temperatures as much as 185⁰ F, and more than 70⁰ F above the ambient air temperature. The cover glass may be plate glass or chemically strengthened glass. Chemically strengthened glass has the advantage of being thinner and lighter. Plate glass has an advantage in that if it does fracture, it typically cracks rather than shattering, a feature known as "frangibility". This is especially true if a laminated solution is used. For public spaces, especially confined spaces such as in transportation applications, management of the broken glass hazard may be critical.

However, the cover glass may also be part of the thermal solution. The polarizers of an LCD, by definition, absorb about 50% of the light that hits them. They are agnostic as to which direction the light comes from absorbing 50% of inbound sunlight as well. Removing the outer polarizer from the LCD and laminating it between the layers of the cover glass puts a few millimeters of glass and an air gap between the absorbed thermal energy and the liquid crystal. This would cut the solar radiation load on the LCD by 50% and also provide the opportunity for passive, chimney, cooling rather than a powered air conditioner. Here, I discus removing the color filter as well. In addition to the brightness benefit, removing the color filter would have some solar radiation benefits as well. Certainly it will obviate any issues with solarization or fading of the color filter.

SpectraVue for Outdoor Signage

When LCDs had terrible viewing angle, many solutions were being developed to fix the issue prescriptively. Of course, the best solution is most always fixing the issue rather than applying a bandaid which is why most of these external fixes were dropped. One of these external fixes was a product called SpectraVue. It consisted of two components, and channel waveguide and a viewing film. The viewing film was an array of cones embedded in a black matrix. Light from the LCD entered the array columnated, bounced off the side of the cones a few times and left the viewing film very dispersed. The film produced an LCD appearance that was virtually the same as a CRT. It was described by Toshiba Labs as "Virtually Perfect viewing angle". Although I have seen several startups and other corporate projects where the intended function of the device depended on building a light funnel, basic geometry shows that funnel structures have exactly the opposite effect on bosons as they do on physical matter. Spectravue takes advantage of this effect to essentially provide something of a photon diode.

Although it was a great solution to the LCD viewing angle problem, it had two problems of its own. The first is that the maker, AlliedSignal, had problems actually manufacturing the product. The second, and more compelling issue was that it was a cost adder. It was being developed at the same time as IPS technology which fixed the problem in the LCD with no additional layers or costs.

Examining the diagram, there is another advantage that SpectraVue had, though it did not count for much at the time. The surface is virtually all blackfill. It adds inherently better sunlight viewability withoug significant loss of display aperture. As IPS development was the reconsideration of an old solution, as I note in my previous post, reconsidering the LCD optical stack might be in order for the digital signage market.

Re-Thinking LCD Architecture for the Digital Signage Market

The original intent of the LCD developers was a hang on the wall Television. However, it was not until 2004 that that really happened, at least for LCD technology. Several things had to happen first. From its emergence as a viable commercial product, color performance had to be accomplished and improved, viewing angle issues needed to be fixed, it had to be cost reduced to affordable levels at 32” and above. All of this was done by about 2004. Shortly thereafter, the use of CRTs in public information displays started to disappear and we had the development of the “digital signage” concept. Previous use of CRTs as public information displays inevitably used “off the rack” consumer product as neither the display makers nor the electronics companies paid much attention to the use of their product as public displays.

Since digital signage has become a recognized market, the differences in product requirements between that and a consumer TV have become more recognized. Although most differences between the two are complimentary: e.g. thinner bezels are beneficial to both consumer TV and digital signage but count for a lot more in the signage market. In some cases, however, the differences between the two are not complimentary and signage needs a solution that would be contrary to product design for a TV. One example is viewing angle. LCD TVs today have great viewing angle: left, right, up and down. In the signage market you probably don’t want that. For overhead signage, photons directed up are completely wasted. Even for eye level signage, the up/down distribution of light would be beneficially focused left to right. For outdoor signage, in areas where there are restrictions in showing video content (especially by roadways) a narrow viewing cone might be called for.

With respect to color, color has always been a tradeoff between saturation and brightness. For outdoor applications, it may be that the loss in brightness is accepted to generate over-saturated colors knowing that they will tend to be washed out in the daylight. Alternatively, a solution could be to go with a black and white, reflective or transflective LCD and do without color. For those displays using a linear polarizer, signage, is most often in portrait orientation, the polarizer should be reoriented for those consumers that might be wearing polarized sunglasses. Finally, as signage displays will face environmental challenges that TVs generally don’t, changing the way the LCD optical stack is put together can have some significant environmental benefits.

Bunny Burgers: Is it Mkt Research or PR

The dearly departed “Spy” magazine did a story where they spoofed several large PR firms regarding a fictitious new chain of fast food restaurants called “Bunny Burgers.” The idea behind the chain was that these QSRs would stock live bunnies, cute ones, and grind them up on the spot to give their customers the absolute freshest meat in their hamburgers. Spy festooned this idea with a fake client with lots of fake money and rented a suite in the Ritz Carlton overlooking Central Park and invited 9 PR firms to bid. Of the 9 PR firms contacted, all 9 were interested in Bunny Burgers as a client and 3 of the 9 were asked to come to the Ritz to discuss the matter. Of the three, none were prepared to turn down the business although one responded seemed diffident about the idea. The other two were quite enthusiastic about it, one even noting how much the public in California would love this idea. The magazine noted, “… as a general philosophical defense of her and her peers, it is important to remember that by the very nature of their profession, they [PR people] are constantly required to represent clients seeking to market stupid, tasteless and even immoral products.”

In a follow up to the PR firm interviews, Spy hired Mark Penn, yes that Mark Penn, to conduct a focus group on the topic. Per Pen’s observations, "Even though we got people to take the first bite, they really wouldn't take a second or third… Scientifically, we tried the concept on them, we tried the reality on them, and most people didn't like either. As well as we could package it, as well as we could add sauce to it, they just didn't like it…. Clearly, if someone tried to go forward with Bunny Burgers, they would have picketers, protesters, riot outside the Bunny Burgers stands, and so the product couldn't make it."

Spy’s conclusion, “For our investigation of the world of fast-food marketing, we discovered a yawning chasm between the enthusiasm of our PR professionals and the outright, unapologetic disgust of the dining public.” Having been around long enough to see several new prospects of the “Technology of the Future” come and go, having seen these technologies of the future accompanied by market forecasts of how this new thing is going to go off like a rocket, I often think to myself, “Bunny Burgers”.

The full Spy article may be found here.