TV Buying Guide, by Alan Lofft -
Although the transistor was invented 50 years ago and most technology (from DVD players to cell phones to stereos) is "solid-state," its still a shock to realize that most of us continue to use a retro vacuum-tube entertainment device thats 75 years old--the cathode-ray tube (CRT) television set. Yes, that 28-inch or 36-inch "picture tube" that we stare at for too many hours a day is just a big, heavy glass vacuum tube with a flat face covered with groups of red, green and blue phosphors that glow whenever a scanning electron beam hits them. The beam traces out the same color image that a camera scans in the TV studio hundreds of miles away.
Invented in the 1930s, the CRT "direct-view" TV set
represents, in the parlance of the engineer, a
"mature" technology, which means its been developed
and refined over the past half-century to a level
that is impressive, affordable, and as good as CRT
can likely get. Admittedly, that clumsy, heavy
behemoth with the glass tube isnt "cool," but
properly adjusted, a conventional TV can still yield
picture quality that ranks with the best.
Even though we drool over those sexy, new thin
flat-panel displays, conventional TV is still the
most familiar and affordable. Heres a rundown on
what to look for in the dependable conventional TV,
either direct-view or rear-projection. To compute
screen size, figure that to enjoy maximum clarity
from a conventional TV, you should sit no closer
than roughly three times the diagonal screen
measurement of the set. So a 36-inch TV screen
should not be viewed closer than 9 feet.
Conventional CRT TV sets
If
you arent interested in High Definition TV or that
new 16:9 "widescreen" picture shape (the aspect
ratio of normal TV is 4:3), you can get a simple
analog set and save a lot of money. The
transition to HDTV is still moving slowly, and
probably wont be complete for another five or 7
years. A conventional analog CRT set will
still let you enjoy superb picture quality from a
DVD player, but it wont display an HDTV image, nor
will it show the film-like images possible from a
DVD player with "progressive-scan" outputs, which
eliminate visible scanning lines. To get that
film-like image, you have to move up to a digital TV
thats HDTV-capable, and if you want the 16:9
widescreen picture tube, the set will run you a
couple of grand or more. But old or not, CRT sets
can deliver stunning high-definition images. Maximum
screen size is limited to about 40 inches, and if
you plan to pull in HDTV signals over the air,
youll need the accessory HDTV tuner, which runs an
extra $500 to $1,000. Most digital cable boxes and
small dish satellite tuners have the option of HDTV
reception (with an upgraded dish).
Big-screen CRT sets use rear-projection (RPTV)-- actually three separate CRT guns for red, green and blue that overlap on the screen and must be precisely "converged," or aligned, from time to time (otherwise youll get color fringes around objects and faces). However, many new RPTV sets have auto-convergence circuits that align the three color guns in seconds, so what used to be a chore is accomplished with a few button-pushes. Rear-projection CRT sets still look their best in dimly lit or darkened rooms, although new RPTVs are remarkably bright. Here again you have the choice between the "old-fashioned" 4:3 screen shape or the HDTV 16:9 widescreen standard. Screen size and HDTV compatibility are the biggest price determinants here, but smaller HDTV-ready widescreen sets between 42 and 47 inches are about $2,000 and up. All HDTV sets have "line-doubling" circuits that receive any conventional non-HDTV signal and convert it to an image free of scanning lines. If youre hungering for high-def TV and you have a budget to consider, rear-projection CRT sets are the least expensive route to true HDTV.
Talked about for decades as the Next Big Thing, the proverbial flat-panel wall-mountable television display only a few inches thick has officially arrived, and now there is a group of new TV display technologies to choose from, all with improvements and some disadvantages. Herewith, a condensed guide to the new displays.
Plasma flat-panel display
Unquestionably
the coolest TV around--its 3 to 5 inches thick and
from 32 inches to 60 inches in diagonal screen
size--the flat plasma panel uses a transparent
electrode behind a glass sandwich that encases
gas-filled cells coated with red, green and blue
phosphors (a second electrode is behind the
phosphors). The electrodes excite the gas, which
then stimulates the red, green and blue phosphors to
glow in the appropriate colors. Plasma panels
are so bright you can view them in a well-lighted
room, and they remain clear and bright over a wide
viewing angle. (By the way, since "pixel" may arise
in this discussion, a pixel is a "picture element"
that comprises a three-phosphor group) .
Downsides? Plasma panels still dont produce true
blacks (theyre more gray than black), theyre
subject to burn-in if youre not careful (an image
permanently imprinted on the screen), and theyre
expensive -- from $3,000US for a 42-inch panel
enhanced-definition (EDTV) unit to $7,000 for the
same screen size in a high-definition-capable panel.
If you want a bigger screen, look at your bank
account--a high-definition (HDTV) plasma panel 50
inches or larger will be $10,000US and up. Prices
are expected to fall by about 1/3 every two years.
LCD flat-panel display
The
liquid-crystal display (LCD) has been around for
more than 20 years. If youve seen a laptop
computer, youre familiar with an LCD flat panel.
It uses an array of thin-film transistors (TFT) that
power liquid-crystal-filled red, green and blue
cells (again, each making up one pixel) in a glass
sandwich. LCD panels have to have a light source to
operate. When the transistors supply voltage, the
liquid crystals untwist, allowing varying amounts of
light to shine through them. As such theyre also
easily adapted to a projector, where a bright lamp
is focused through the LCD chip. LCD flat panels
arent nearly as popular as plasma displays, and
screen size is limited to about 37 inches, with
prices into the $8,000US range. LCD projectors
can be very bright and are capable of very
accurate color rendition as well as HDTV resolution,
but prices are high, into the $6,000 range or more.
They also have the most trouble producing a true
black, because whether in a flat-panel or projector,
light always has to pass through the LCD chip.
(Unlike a plasma display, the LCD panel doesnt
originate light.) And as youve likely noticed with
laptop computer displays, they arent viewable over
as wide an angle. If low in resolution or clarity,
LCD images can exhibit a "screen-door" effect, where
each pixel becomes visible. But like DLP projectors
(see below) LCD models are quite compact and
lightweight, often 10 pounds or less.
DLP rear- and front-projection TV
Apart
from the flat-panel plasma displays, digital light
processing (DLP) chips are the newest and
most talked about TV technologies. At the heart of
all DLP devices is a 16:9 digital micromirror chip
made by Texas Instruments. A high-intensity bulb is
focused with a lens towards the DLP chip, whose
surface is covered with nearly a million tiny
pivoting mirrors that reflect light from the bulb
onto a screen. Color is derived by filtering the
light through a color wheel. The DLP chip is a huge
advantage in a rear-projection set because the set
can be made relatively thin (about 16 inches) and
lightweight (75 lbs.) compared to cumbersome CRT
sets. DLP rear-projection sets can be very
bright with excellent high-definition clarity
and although they are more expensive (about $4,500US
for a 50-inch screen), they arent nearly as costly
as high-def plasma panels or LCD. Used in a front
projector, DLP is remarkably compact (the size and
weight of a slide projector) and capable of quite
bright, contrasty images with blacks that are better
than plasma or LCD-based displays, almost as good as
CRT blacks. And because the mirrors in the chip are
integral to it, DLP projectors dont have
convergence problems, nor are they subject to
burn-in of images like plasma panels. DLP is still
an emerging technology and some images can be
subject to a "rainbow effect" if you glance quickly
at the screen (Ive never seen it, but some critics
comment on it). Many DLP front projectors range in
price from as little as $1,500US to $6,000,
depending on the projectors' HDTV capabilities. DLP
technology also requires regular maintenance. Bulb
life is about 2,000 hours (depending on your
projector) and the bulbs cost about $450. For an
affordable compact device free of convergence
adjustments, DLP may well be the future of
front and rear TV projection.
