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.