The different types of HDTV

There is a wide array of display technologies now available in the market.  Many years back, CRT (Cathode Ray Tube) was the only technology available.   Today, LCD (Liquid Crystal Display), Plasma and DLP (Digital Light Processing) are the competing HDTV displays you will find when you go to the store.  How do these display technologies differ and which one is the best?  We will try to answer these questions by providing the basic principles behind each technology and a comparison of their advantages and disadvantages.

Display Technologies

CRT or cathode ray tube display technology is based on vacuum tubes that contain electron guns and fluorescent screens.  Images are formed directly on the screen at the end of the tube opposite the guns.  They are available in screen sizes up to 40 inches and going larger than this is not practical because of weight issues.  There are very few CRTs produced with HDTV capability.

Pros:

• Best black response
• Highest color performance
• Smooth gray-scale response
• No motion artifacts
• Widest viewing angle

Cons:

• Low contrast for fine text and graphics
• May produce some image flicker for refresh rates below 75
• Largest direct-view CRT screen size is only 40 inches
• Periodic adjustments and calibration required for critical applications
• Bulky and heavy

Plasma is a type of flat panel display technology based on gas made up of xenon and neon.  Each pixel is made up of individual RGB light emitters that when lighted convert the gas into plasma.  This then excites the phospor coating of the screen to produce the picture images.

Pros:

• Good black response
• Good color quality
• High contrast images, including fine text and graphics
• Wide viewing angle
• Fast screen refresh rate making it suited for fast moving pictures
• Largest direct-view display technology available

Cons:

• Suffers from screen burn that is the result of lost phospor luminosity in certain areas due to prolonged usage.
• Suffers from image retention (similar to screen burn) when some pixels are run at high brightness for a prolonged period.  But this is only due to charge build-up and there is a self-correction  process after power down.
• Screen Door Effect due to gaps between pixels
• Display technology makes products heavy and bulky

LCD TV technology is based on liquid crystals which align themselves when activated by electric current.  This alignment process, in conjunction with polarized color filters and a source of light sitting at the back of the screen produces the picture images on the screen.

Pros:

• Longer screen life
• No screen burn from stationary images
• Better glare response
• Lesser power consumption
• High contrast images, including fine text and graphics
• Brightest of all the display technologies
• The thinnest displays available and not very heavy

Cons:

• Slowest refresh rate of all the displays
• Brightness and color response decrease as the viewing angle increases
• Screen Door Effect due to gaps between pixels
• Possible uneven light distribution from the backlight

DLP (Digital Light Processing) is actually a rear projection technology wherein the CRT projectors are replaced by microchip projectors.  The picture image is created by tiny mirros laid out in a matrix of a semiconductor chip called Digital Micromirror Device (DMD).  Each mirror represents one pixel so the number of mirrors is equal to the resolution of the projected image.

Pros:

• Microchip mechanism makes it possible to manufacture lighter and larger screen sizes.
• Darkest black-level and highest dynamic range
• Closest color response to older CRT direct view displays
• High pixel fill factor produces a smooth and sharp image
• Very fast pixel response times and few motion artifacts

Cons:

• Color wheel rainbow artifacts
• Direct-view display not available
• Noise from the color wheel and cooling fans

Comparison of HDTV Display Technologies:

All of the HDTV displays that we discussed produce very good picture quality but there was no single winner.   Each uses a different technology so we cannot really do an actual apple to apple comparison between them.  Aside from the technical parameters used in the discussion, other factors to consider are price of the display device and the viewing environment.

If you require only a 40 inch or smaller display, and you are on a tight budget, then you can settle for CRT which is a clear winner when it comes to image quality.  The problem with this is there are a very limited number of HD-capable CRT displays in the market today.  If you require a thin display at 50 inch or larger sizes, then plasma is the choice.  It is the better choice when it comes to color quality, black response, refresh rate and better value for your money in screen sizes 50 inch or bigger.  For home theater purists and enthusiasts, plasma is highly recommended.  For those looking for smaller screen sizes but want something stylish and slim, LCD TV can be a good choice.  LCD TV has the added advantage of longer screen life and lesser power consumption.  It also does not suffer from screen burn so LCD can also be considered if the display will also be used for computer applications.  For very large screen sizes, DLP is the overall winner when it comes to image quality.  This is the clear choice if the requirement is for larger home theater venues or small digital cinemas.