Inner Workings: Inside a Slim-Cabinet Rear-Projection TV
Clearly embedded somewhere in America's national psyche is an obsession with getting thin. How else do you explain both the celebrity of Nicole Richie and the craze for flat-panel TVs? In fact, with the increased focus on TVs slim enough to be mounted on a wall, the environment for rear-projection HDTVs has gotten a lot tougher.
The irony is that while fewer rear-pro models are being sold each year, there's still quite a bit of innovation going on in that category. But it's hard for rear-pro sets to compete with flat-panel displays when it comes to sex appeal. Compared with a wall-mountable plasma or LCD set, even the shallower rear-projection models still come off like Kirstie Alley post-Jenny Craig - thinner, yes, but not exactly skinny.
That's why companies have been working feverishly to shave a few inches off the depth of their rear-pro cabinets. The current "Biggest Loser," at just 10.8 inches from front to back, is JVC's 58-inch LCoS model (reviewed in June). To see how JVC did this, it's helpful to know how an LCoS set works. LCoS is a "reflective" technology, where light is bounced off a coating on a silicon chip. When voltage is applied to the chip's liquid crystals, they act like tiny gates that regulate the amount of light reflected onto the projection screen.
JVC calls its version of the LCoS technology D-ILA (Direct-drive Image Light Amplifier). And it uses a three-chip design, with a separate LCoS panel dedicated to each of the primary colors (red, green, and blue).
In an LCoS TV, light from a high-intensity lamp is first sent through a condensing lens, which focuses and directs the beam. The focused light then goes through a polarizing beam splitter, which separates the white light into red, green, and blue. In the JVC, each beam then hits one of the three LCoS panels. The panels have a layer of liquid-crystal cells sandwiched between a silicon semiconductor (which contains the driver circuitry that regulates voltage) and a clear glass plate. Behind the semiconductor, which has a reflective coating, is the printed circuit board.
The liquid crystals regulate the amount of light striking the semiconductor's shiny surface. The light is reflected back through the liquid-crystal layer and into a prism, where the three beams converge in a single, full-color image. That image is then sent to the projection lens, where it's magnified before being bounced off a flat mirror at the rear of the cabinet that sends it forward to the back of the projection screen.
JVC uses a concave mirror and a refracting lens to create an optical engine with a wider projection angle than that used in other rear-pro sets. With a concave mirror, as opposed to the convex ones usually found in projection TVs, the beam is focused before it hits the screen, allowing the use of a small-beam projection unit. As a result, these sets can generate a projection angle that's 138° wider and 1.5 times greater than that of previous models, allowing JVC to cut the required projection distance by 40% and thereby reduce cabinet depth.
With flat-panel TVs getting larger and less expensive every year, the future for rear-projection sets seems cloudy. But they still offer the least expensive path to big-screen home theater excitement. And based on JVC's ultra-slim models, there's no longer any reason for you to live with a big hulking presence in your living room or den - unless it's your significant other.