New display concepts are a dime a dozen. However, very few of them find their way beyond prototype stage, and even if they do, they usually can’t compete with the manufacturing muscle of the $100 billion liquid crystal display (LCD) industry. But a display startup called Prysm believes that its technology, called laser phosphor display (LPD), has the perfect combination of picture quality, energy efficiency, and manufacturing simplicity to have a chance of breaking through.
The San Jose-based Prysm, which came out of stealth mode last week, has been getting plenty of media attention due to its claims of energy efficiency. According to Roger Hajjar, the company’s chief technology officer, an LPD consumes a fourth of the power of a liquid crystal display with the same brightness and about a tenth of the power of a plasma screen (although an LPD also shines brighter than a plasma screen, so the comparison isn’t direct, according to Hajjar).
“The physics is simple,” says Hajjar. In other displays, he says, “the light source is mostly on and there’s a threshold power requirement even to keep the screen black.” In an LPD, he says, the lasers get to rest where the screen is dark, saving power.
The concept behind LPD is relatively straightforward. Beams of light from several ultra-violet lasers are directed by a set of movable mirrors onto a screen made of a plastic-glass hybrid material coated with color phosphor stripes. The laser draws an image onto the screen by scanning line by line from top to bottom. The energy from the laser light activates the phosphor, which emits photons, producing an image.
An LPD differs significantly from a LCD, in which a backlight, made of either white LEDs or a cold-cathode florescent light, shines through layers of optics, including color filters and liquid crystals, to produce an image. More than 90 percent of the original light is lost in this process. Another competitor, plasma display technology, consists of small cells of ionized gases that emit light–a process that requires a relatively large amount of power. And a conventional laser television, such as the LaserVue, made by Mitsubishi, uses red, blue, and green lasers and a micromirror device that combines and directs the light. This is essentially a rear-projection display, but because of its high price tag, it hasn’t become widely popular.
Crucially, Hajjar says, larger LPDs are also energy efficient compared to today’s larger displays, such as electronic billboards. Compared to an LED billboard, where each diode is a pixel, an LPD of the same size and brightness eats up only about a tenth of the power, since fewer lasers are used compared to the number of LEDs required for the billboard.