Pro AV Logo Originally published as a Consultant's Connection
column in Pro AV Magazine
  January 2003

Plasma Displays – Bright and Beautiful,
But By What Standard?

The AV industry seems to be overwhelmed with either an excess of standards (in digital audio. for example) or too few standards—as it is for AV systems specifications and drawings. Going back to the basics of analog audio, however, we find some long-standing standards still being used.

By Tim Cape, CTS-D

There are standards and then there are standards. The AV Industry seems to be overwhelmed with either an excess of standards (in digital audio, for example), or too few standards – as it is for AV systems specifications and drawings. Going back to the basics of analog audio, however, we find some long-standing standards still being used, and they really are standards. Terms like dBu, dBV, loudspeaker sensitivity, signal-to-noise ratio, and THD are measurements we see in a lot of audio specifications, and they are relatively easily verified as illustrated in reviews and workbenches the world over. However, when it comes to the visual part of audiovisual, standards aren’t so standard – especially for plasma displays.

On Display

When choosing a display device, there are five basic categories of information I want to know about it: image size, inputs, control features, reliability and visual specifications. Image size and inputs are easy. How big is the image area? What connectors does it have? How many are there? What formats does it support? What bandwidth can it accept? Are there audio inputs? These aren’t hard to figure out and the formats involved are based on well-established standards, otherwise the inputs wouldn’t work.

Control features of a display can be a bit squirrelly, but with a little perseverance one can find out what the RS-232 control codes are, if the control systems manufacturers have them in their library, whether there is Ethernet as well as RS-232 control and whether the two ports be used simultaneously. There are also the issues of on-board computing and wireless control capability, but these are easy to determine (if not easy to use). And Ethernet and RS-232 are standards-based.

Reliability can be an issue for certain products or manufacturers, but this is something that there aren’t many standards for today. We don’t have a Consumer Reports for Pro AV that will poll integrators and consultants and publish the reported failure frequency and repair rates of manufacturers on a regular basis. But we can sometimes obtain mean time between failure information from the manufacturer. Beyond that, anecdotal feedback from others in the industry as well as personal experience with a product play an important part in evaluating a display’s reliability.

The fifth category – visual specifications – is the squirrelliest. What we really want to know about this aspect of a display device is the resolution, the brightness, and the contrast ratio. Is it too much to ask that these numbers be applicable to the real world? In audio, a loudspeaker’s sensitivity, power rating and coverage pattern are standard specification items we can expect to find for any good Pro AV loudspeaker. And though some may grumble about the accuracy of some of the data, these numbers are usually in the ballpark of reality. Can the same be said for display specifications?

The native resolution of a display is straightforward, but we seem to get into trouble when it comes to brightness and contrast ratio – the two most important design parameters after image size for determining the suitability of a display device for a particular application. These numbers determine how much ambient light can be allowed on the screen and may limit how big the image can be for a given screen type and lighting condition. For projection devices, independent reports confirm that projectors will usually measure up to their published specifications or at least to within striking distance of them. Yet there seems to be a lot more variety in the reported specifications for plasma displays.

The Standards

 
Contrast Test Pattern
 

The image above illustrates the ANSI standard black and white test pattern to use for contrast ratio measurements. With plasmas, measured contrast ratio can vary widely if the total screen area is driven by less or more than the total 50% white area indicated or if the driving electronics are modified.

The procedures for measuring the brightness, contrast ratio and other parameters of a fixed resolution projection device are established in the ANSI (American National Standards Institute, Inc.) document entitled “American National Standard for Audiovisual Systems – Electronic Projection – Fixed Resolution Projectors” designated as ANSI/NAPM IT7.228-1997 (available from www.ansi.org). The Secretariat responsible for penning this standard is the National Association of Photographic Manufacturers, Inc. It contains very detailed procedures and requirements for measuring and reporting a variety of projector parameters, and this standard is the basis for procedures used by most manufacturers to obtain their specification numbers for both fixed resolution projection devices and direct view devices such as plasmas.

ANSI Test Pattern
 

The ANSI standard calls for 9 points of measurement to obtain ANSI lumens or ANSI nits (candelas/m2).

 

There are additional documents prepared by the Data Projector Committee of the Japan Business Machine and Information System Industries Association (JBMIA, formerly the Japan Business Machine Makers Association. Their document “Guidelines for LCD Projector Measuring Procedures and Measuring Conditions” is less detailed but is based almost entirely on the ANSI standards.

The problem is that there is no regulation (self or otherwise) to make certain that the standards are being followed to the letter or that any variations in the procedures are reported. Unlike LCD and DLP technologies, measuring plasma displays can be a lot more variable due to the differences in the technologies. For example, making plasma display brightness measurements “pre-filter” before the final anti-glare coverings are installed, adjusting the plasma driver algorithms to produce brightness levels that aren’t sustainable in real life, and using smaller areas of white than the ANSI standard calls for can create exaggerated brightness and contrast ratio measurements that are not attainable in the field. Independent tests on production units confirm that these specifications can be off by a factor of two or more when the standards are strictly applied to an off-the-shelf display.

To make things more confusing, there is a shell game of sorts with whose plasma glass component is used in whose finished products. These relationships are changing all the time, but one example is that Fujitsu and Hitachi share a manufacturing facility and use the same glass for many of their competing displays, but Fujitsu also uses Pioneer’s glass for their 50” display. Manufacturers who make a 61” plasma use NEC’s glass. All 63” plasmas use Samsung’s glass. And so on. Not that there’s anything wrong with that. The manufacturers are usually willing to disclose who is using what glass, but you do have to ask. This is just more useful information to have when comparing plasma specifications and evaluating whether it’s the glass or the front-end electronics that makes one plasma perform better than another.

Know what you don’t know

Ultimately, even in the Pro AV industry, an educated consumer is a better consumer. And consume we do. Knowing the background of how these specifications can vary can help us have more of a trust-but-verify methodology in selecting which products to use. We can then also focus more on the other quality issues such as internal video scaling and processing that affect the perceived video quality of signals not matching the native resolution of the display instead of playing a purely numbers game that doesn’t have fixed rules.

To their credit, some manufacturers have pulled out of this game and don’t publish brightness or contrast ratio data for their plasma displays, but this also further undermines the purpose of having a standard to follow that allows consultants, contractors and consumers to have reliable published data on which to make informed design decisions.

 

 

 
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