LED LCD vs Plasma

The shift from conventional fluorescent lamp (CCFL) backlighting of LCD HDTV to LED (light-emitting diodes) provides performance benefits that changed the comparative standing of LCD and plasma HDTV. We compare performance data for two premium model LED LCD (Samsung UN46B8500 and LG 47LH90) and two premium model plasma HDTVs (Samsung PN50B860 and Panasonic TC-P54Z1) in conjunction with an examination of the technology differences between the two display formats.

LED LCD

LED LCD and Plasma Display Technologies in Brief

LCD displays work by filtering a backlight while plasma displays have vast arrays of colored sub-pixel plasma cells which glow when charged. LED LCD displays still use liquid crystals for light filtering but, have hundreds of LED as backlighting instead of a fluorescent lamp. LED backlighting can be either edge-lit or full array with the full array backlighting combined with local dimming having a performance advantage in terms of black levels and contrast ratios. Plasma cells are distributed evenly across the display and being light emitting do not require the light filters and diffusers (full array models) of LCD HDTVs.

Improvements brought by the switch to LED backlighting include; better contrast, wider range of colour reproduction and deeper black levels, reduced energy consumption and the elimination of mercury in production.

Display Dimensions

Modern HDTV have been shrinking in depth and all four HDTVs examined have a depth in the one inch range. As can be seen full array LED LCD cannot be made as thin as edge-lit LED LCD.

Due to plasma pixel size limitations plasma HDTVs have size restrictions which generally limit the minimum size of plasma HDTVs to about 40 inches.

Contrast ratio

A high contrast ratio is an important element in producing high quality image reproduction. Most HDTV manufacturers have increased the contrast performance of their displays by dynamically altering backlight brightness based on the overall brightness level of the frames/scenes being reproduced. Poor contrast ratios are evidenced by the loss of much detail in both brighter and darker scenes.

It has been generally accepted that plasma televisions have better contrast ratios than fluorescently backlit LCD panels due to the fact that a plasma television can completely turn off the light source for individual segments of the screen. However, the latest full array LED backlight technology allows the television to individually control backlight segments so the backlighting matches the distribution of lighter and darker areas required by the image being displayed. This technology allows for dynamic contrast ratios similar to and even exceeding those produced by plasma television panels. This is evidenced by the results in the comparison table where the Samsung B8500 LED LCD leads by a fair margin due to being a full array LED LCD with local dimming as opposed to edge-lit.

When compared to full array backlighting LED LCD, plasma displays have lost the significant contrast ratio advantage they have held over conventional LCD HDTVs.

Colour

A wider, more vibrant color range equates to more realistic pictures. Plasma displays do not create the RGB sub-pixels by filtering the backlight as with an LCD displays and have a wider range of color reproduction from the scintillator materials available. It has meant they have enjoyed a color reproduction advantage over conventionally backlit LCD HDTVs.

An advantage of the shift to LED backlighting is its provision of a wider color gamut compared to conventionally backlit LCD televisions due to the purer white light produced by while LEDs. LED’s cover a broader range of red and greens up to 114 percent of the NTSC standards. With being able to display a more extensive range of colors, comes the attribute of colors being more natural or lifelike as they are closer to the human eye’s color perception range. It should be noted that Sony uses clusters of different color lasers which when combined produce and even purer white light than that achieved by white LED. As a consequence the color gamut and color reproduction of these HDTVs is a step ahead of those using white LED.

LED LCD displays have closed the color performance gap plasma displays enjoyed over conventionally lit LCD displays.

Motion Sharpness

A rapid response time is essential for sharp fast onscreen motion (think sports and action movies) reproduction without blurring. The rapid electrical discharging of the individual cells which make up pixels give plasma displays an ultra fast response time measured in single digit micro seconds (0.001ms – milliseconds).

Although LED display response times have been reduced to single digit milliseconds, significantly improving the handling of fast motion, they are still a thousand times slower than the response time for plasma HDTVs. In the comparison table, the Samsung B860 plasma HDTV has a 0.001 ms response time compared to 2 ms for the Samsung B8500 LED LCD HDTV.

To create smoother onscreen motion HDTV manufacturers have been interpolating extra frames for display resulting in higher refresh rates of 120Hz and even 240Hz for LCD HDTV. The extra frames provide intermediate positions for moving objects resulting in an apparently smoother motion. Plasma displays, including the two models examined, advertise their 600Hz technology where up to 10 sub-fields are created to smooth motion.

LED backlighting has not had any direct effect on motion smoothness as it is primarily a video processing improvement.

Brightness

Traditionally LCD HDTVs with their superior brightness have been the preferred choice for bright viewing environments. Plasma display brightness levels have improved and now come with glare reducing films/coatings which reduce light reflection (reflections destroy image quality) however, the new super bright LED backlighting displays maintain the advantage for LCD displays.

Viewing angle

Very wide viewing angles have always been an advantage of plasma displays over conventional fluorescent lit LCD displays. Wide viewing angles ensure that dimming, contrast loss and color shift at larger angles from the display centreline occur are minimized.

Although manufacturers have claimed wide viewing angles for fluorescent lit LCD displays, they mostly exhibit some significant deterioration beyond 30 degrees from the displays centreline. LED televisions have superior viewing angles, up to 70 degrees off centreline, compared to conventional LCDs due to their decentralised backlight distribution.

Plasma displays still have superior viewing angles but LED LCD HDTV are catching up and it depends on the viewing situation as to whether the difference will be of concern or not.

Display Panel Lifespan

With both LED LCD and plasma displays having rated lifespans of 100,000 hours there is no significant advantage to either display technology in this respect.

Improvements in plasma display technology including functionalities such as screensavers and image-shifting have previously eliminated burn-in as an issue of concern.

Power Usage

Energy-efficient backlighting allows LED LCD televisions to have an energy consumption of up to 40 percent less than conventional fluorescent backlit LCD televisions.

Some significant gains have been made with improving the comparatively higher power usage of plasma HDTV – eg. Panasonic NeoPDP display technology. However, LED LCD displays continue to maintain a lead in energy consumption.

For the four LCD and plasma displays compared the plasma panels have power use 57 percent higher power usage than the LCD HDTVs (when compared on energy use for the same display area).

Environmental Impact

Conventional CCFL backlights contain some mercury leaving a safe disposal problem. LED backlit LCD displays can be manufactured to conform to the European Union’s RoHS initiative to restrict the use of certain hazardous substances in electrical and electronic equipment. The Directive bans the placing on the EU market of new electrical and electronic equipment containing more than agreed levels of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants.

Plasma HDTVs have been the favoured display technology for the environmentally conscious (or aware) however, LED LCD displays have now closed this gap.

Price

Of the four premium 1080p resolution HDTVs examined in the comparison table the LG 47LH90 LED LCD at $1,700 comes in well below the other models. Which reflects the significant cost difference between edge-lit LED LCD and full array LED LCD The only significant feature difference is the lack of content provision through an Internet connection.

In the Future

While Samsung has produced both full array and edge-lit LED LCD to date, it has announced that it will in future be producing only edge-lit models due to performance improvements it has made in this LCD display type. It is also known that manufacturers are working to successfully marry edge lighting with local dimming.

Update – Quantum Dot LED LCD Technology

Quantum Dots, a nano technology, promises to deliver significant performance improvements to LED LCD displays. It has been claimed that Quantum Dot technology will deliver to LED LCD displays; 40 percent efficiency improvement, a color gamut over 100% NTSC and improved contrast. The technology is expected to be integrated into consumer LED LCD displays by 2011.