Waveform 09 FPD and Digital Displays

[HD Library]

Originally published 10/28/2004, HDTV Magazine, editor Dale Cripps

Updated 08/12/2005

By Richard Fisher

We start our FPD discussion with the oldest FPD on the market, LCD. This has been around for over 10 years and has improved dramatically. While greatly improved over the last decade plus further refinements over the last year or two LCD front and rear projection displays can still suffer from poor fill factor and does not meet the 3 screen height spec of HD for viewing distance. In practice we are using 4-5 screen heights to get the pixels to disappear. While burn-in is not a problem the heat from the lamp can destroy the LCD panel after many years of use but I do not have a time frame in viewing hours for you; from experience 8-12 years is when this can show up but it is a function of hours used. The LCD panel used for projection is based on light passing through or being blocked. LCD front and rear projection do not have good black levels but that is changing with front projection using an iris and will be covered later in this article. Both typically require bias lighting for optimal results. While recommended for casual viewing it does have videophile potential provided you are aware of the limitations. A bright display for medium-to-bright rooms. HD product uses three 720P panels with excellent uniformity. LCD RPTV uses an outside diffuser anti-glare screen that will create a frosted look or artifact with bright areas of an image.

DiLA, LCoS and SXRD front or rear projection offers a different variation of LCD based on reflectivity. These panels provide great fill factor and pixel visibility is of no concern with excellent uniformity. Unfortunately they are about equal if not slightly worse than LCD with black levels and bias lighting is required as well. Burn in is of no concern. DiLA front projection have quite a buzz in videophile circles. Rear projection versions of either are best for casual viewing due to the black level problem. The LCoS which I have seen in the stores use the same outer lenticular screen as CRT so no frosted imaging. All versions use three HD 720P or 1080P panels which is what has created most of the buzz with this technology and is a good example of how resolution must be balanced against other imaging factors. A bright display recommended for videophiles or casual viewing in medium to bright rooms.

DLP is probably the most exciting technology in the HD world of FPDs. Each pixel is actually a tiny mirror that reflects light to the lens or to a light absorbing area within the light cavity for black. While similar to the above for performance in the early years much has happened over the last 2 years threatening the reign of front projection CRT. Fill factor is good and comes very close to meeting 3 screen heights viewing distance with excellent uniformity. Rear projection DLP on the other hand still suffers from poor black levels for dark room applications. Some are three HD 720P panels but most are a single panel and use a color wheel to create the red, green and blue primaries. This method can cause an artifact called rainbows that many have found annoying and for a minority causes viewer fatigue. Much of this has been due to color wheel design and/or the use of high gain screens. Current generation appears to have overcome this for most folks by using a 7 segment color wheel rather than the 5-6 segments used in the past but this is offered in respect to front projection applications. Rear projection DLP still has this problem due to the high gain screen used. One potential solution is to implement an archimedes spiral rather than RGB sections for the color wheel but this has yet to be applied. Every front projection DLP I have seen has been current product installed in the correct viewing environment producing awesome imaging unheard of just 1-2 years ago with no rainbow artifacts to be seen.

DLP will also be presenting it