Transparent video walls
Transparent video walls combine transparent LCD screens with a video wall controller to display video and still images on a large transparent surface. Transparent displays are available from a variety of companies and are common in retail and other environments that want to add digital signage to their window displays or in store promotions. Bezel-less transparent displays can be combined using certain video wall controllers to turn the individual displays into a video wall to cover a significantly larger surface.
How it works
There are two major see-through display technologies, LCD and LED. The LCD technology is older, though OLED see-through displays are becoming more widely available. Both technologies are largely derivative from conventional display systems, but in see-through displays the difference between the absorptive nature of the LCD and emissive nature of the OLED gives them very different visual appearances. LCD systems impose a pattern of shading and colors on the background seen through the display, while OLED systems impose a glowing image pattern on the background.
Any LCD panel is by nature “see through,” though conventional LCDs have relatively low transmission efficiency so that they tend to appear somewhat dark against natural light. Unlike LED see-through displays, LCD see-throughs do not produce their own light but only modulate ambient light. LCDs intended specifically for see-through displays are usually designed to have improved transmission efficiency. Small scale see-through LCDs have been commercially available for some time, but only recently have vendors begun to offer units with sizes comparable to LCD televisions and displays. Samsung released a specifically see-through designed 22-inch panel in 2011. As of 2016, they were being produced by Samsung, LG, and MMT, with a number of vendors offering products based on OEM systems from these manufacturers. An alternative approach to commercializing this technology is to offer conventional back-lit display systems without the back light system. LCD displays often also require removing a diffuser layer to adapt them for use as transparent displays.
The key limitation to see-through LCD efficiency is in the polarizing filters, which inherently limit the transmission efficiency for unpolarized light to 50% or less. Inexpensive polarizing films also have relatively low transmission efficiency, though commercial development efforts have had some success in improving it.
LED screens have two layers of glass on both sides of a set of addressable LEDs. Both inorganic and organic (OLED) LEDs have been used for this purpose. The more flexible (literally and figuratively) OLEDs have generated more interest for this application, though as of July 2016 the only commercial manufacturer Samsung announced that the product would be discontinued. OLEDs consist of an emissive and conductive layer. Electrical impulses travel through the conductive layer and produce light at the emissive layer. This is different from LCDs in that OLEDs produce their own light, which produces a markedly different visual effect with a see-through display. The narrow gap between the pixels of the screen as well as the clear cathodes within allow the screens to be transparent. These types of screen have been notoriously difficult and expensive to produce in the past, but are now becoming more common as the method of manufacturing them is advancing.