At the 2006 Consumer Electronics Show (Jan. 5-8; Las Vegas, NV), light-emitting-diode (LED)-illuminated MDTVs (microdisplay-based rear-projection TVs) made a big splash with five demonstration systems in public view. The first crop will reach market by mid-2006, with laser-based MDTVs following about two years later.
While MDTVs are typically powered by a high-intensity arc lamp called an ultrahigh-performance (UHP) lamp, developers want to replace these lamps with solid-state sources like LEDs and lasers.
Microdisplay TVs have been a hit at retail, where they are rapidly replacing CRT-based rear-projection TVs. But they face big pressure from plasma-display TVs and now LCD TVs in the greater-than-40-in. size category. While MDTVs still have some price advantages, this is eroding so developers need new innovations to avoid losing market share. Enter LED and laser sources.
The benefits of LED or laser illumination are substantial and real. By replacing the UHP lamp, the lifetime of the light source can be extended from perhaps 6000 to at least 20,000 hours. Laser or LED illumination can typically achieve more than 120% of the NTSC (National Television System Committee) color gamut, creating much more saturated colors, especially in the red. Plus, LEDs and lasers offer instant-on operation, have no mercury (like UHP lamps), consume less power, and run considerably cooler than UHP lamps. In addition, black levels (and contrast) should improve as the LEDs or lasers can be turned off or way down for darker gray levels-something that an iris must do with UHP-based systems.
Lasers also offer new ways to create projection systems. For example, 0-D systems can be created that rely on 2‑D scanning to create an image with a point of light. 1-D systems use a line-scanning systems and 1-D modulator, whereas 2-D systems use a conventional microdisplay and area illumination. All have tradeoffs that need to be evaluated.
The downside of using LEDs is that high-density, high-brightness devices are needed that can cost more than a UHP lamp. They are extended sources of light that need to be coupled into a projection system in an efficient manner. Plus, the sets will need to be sold with a premium in pricing and a “total cost of ownership” message over the cost of buying a replacement lamp, which could slow adoption.
Major concerns for laser illumination include speckle, cost, and safety. Reducing speckle is required for good image quality, and understanding the safety concerns and approvals needed for laser displays will be challenging. But cost remains the most significant hurdle. Red, green, and blue laser light for displays can be produced today in the desired power levels, but the cost is prohibitive. Developing technology that can meet the power and cost requirements to replace a UHP lamp has been elusive.
Breakthroughs were on display at CES in LED and laser sources. Leading the charge for LEDs is Luminus Devices (Woburn, MA). The company has developed a new type of LED emitter it calls a PhlatLight that adds a photonic-lattice network above a surface-emitting LED wafer. The net effect is high brightness per unit area-an achievement that has now made the commercialization of LED MDTVs a possibility in 2006. The LEDs are offered in red, green, and blue colors.
On the show floor were LED-based MDTVs from Akai, Samsung, Hewlett Packard, JVC, and Sanyo. JVC and Sanyo are not yet committed to commercialization, but the other three are. Expect to see a 56-in. MDTV from Samsung by May for $3999, a 52-in. MDTV from Hewlett-Packard by August for $2499, and 52- and 46-in. sets from Akai this spring starting at less than $2000.
Frequency-doubled lasers
On the laser side, Novalux (Sunnyvale, CA) offered impressive demos. It has developed a laser architecture called Novalux extended-cavity surface-emitting laser (NECSEL), a solid-state laser technology that uses IR lasers, nonlinear frequency-doubling crystals, and an output mirror/coupler to create green and bluew laser light. The surface-emitting gallium arsenide lasers are doubled to the desired green (532-nm) and blue (460-nm) laser light. These are assembled in a compact copper housing for good heat extraction. For the red wavelength (635 nm), no frequency doubling is necessary as a direct edge-emitting semiconductor laser is used at this wavelength.
Last August, Novalux delivered green lasers that offered 500 mW of output power. By November, it reported delivering blue lasers to early customers that also featured 500 mW of output power. At CES this year, the company announced it had achieved green and blue lasers with output powers of 1.5 W each. The company forecasts it can achieve 4 W for green and blue perhaps as early as the end of 2006.
According to optical and color-space modeling done by Insight Media, an MDTV in the mid-50-in. size range with a medium-gain screen and 2-D architecture will require about 2 W per color to create a desirable image. As a result of Novalux’s latest demonstrations, this goal is now within sight. Novalux can also tailor the output of the laser to enable the creation of multi-primary-laser display systems.
At CES, Novalux demonstrated two MDTV laser-based prototypes: a 47-in. 3-LCD (liquid-crystal display) MDTV and a 52-in. MDTV using DLP (digital light processor) technology (see figure). A reference UHP-based MDTV was also shown. The baseline UHP-based MDTV offers about 400 Cd/m2 of on-screen brightness. The same TV with the laser source offers about 250 Cd/m2 while the DLP set produces about 300 Cd/m2.
The laser-based sets were noticeably dimmer than the UHP set and will need improvement. The DLP system appears to be more light efficient. The speckle from the laser sources is quite obvious and will not be acceptable in any commercial product. Novalux is said to have some speckle-reduction technology, but this was clearly not implemented in these demos.
On colorimetry, the color gamut is clearly expanded and more desirable compared to the UHP-based pallet. However, the gamma of the electronics had been optimized for UHP light, so the full potential of the laser sources was not on display here.
All this development activity will turn the heat up in the big-screen TV market. Manufacturers will likely want to consider putting LED or laser-based displays on their roadmaps. The technology is not limited to projection; LCDs will benefit from these sources too.