The Economist - USA (2021-01-30)

The EconomistJanuary 30th 2021 Science & technology 65

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illuminated and unilluminated pixels.

The upshot of these various strengths

and weaknesses is that led tvs have bright,

high-definition images, while pictures dis-

played on oled tvs have richer colours and

more contrast. Moreover, lacking a back-

light, oled tvs can be made slimmer and

lighter than the ledvariety. oledscreens

are, however, trickier to manufacture. tvs

made with them are therefore more expen-

sive—sometimes more than twice the price

of a similar sized ledtelevision. For the

customer, it is thus a matter of, “you pays

your money and you takes your choice”.

One answer to the backlighting pro-

blem is to call on the services of micro

leds. Unlike standardleds, these are small

enough to be assembled like oleds into

image-forming pixels. Both Samsung, in

the form of a monster called The Wall,

which measures 146 inches (3.7 metres)

from corner to corner, and Sony, a Japanese

firm, in the form of a product called Crystal

led, have micro-ledsystems built from in-

dividual screen modules which can be as-

sembled to make displays of various sizes

for commercial use in places like sports

stadiums. Now, though, micro-ledtelevi-

sions aimed at the retail market are on their

way. At this January’s Consumer Electron-

ics Show (ces), held online rather than, as

is more usually the case, in Las Vegas, Sam-

sung unveiled a 110-inch micro-ledtelevi-

sion constructed as a single unit. This, it

says, will be the first in a new range of tvs

of various sizes that will go on sale later

this year. Television aficionados will,

though, need deep pockets to buy one. Re-

ports from South Korea suggest the new

model will cost more than $150,000.

Quantum mechanics

That will not last long. All new electronic

technologies start off being expensive in

this way. When Westinghouse brought out

the first colour tvin 1954 it cost $1,295,

equivalent to some $12,500 today. By the

1960s colour televisions could be bought

for a few hundred dollars. If new devices

are successful, prices tumble as produc-

tion volumes increase. Lining up 24m indi-

vidually controlled micro leds, each only a

few microns across, with the precision

needed for them to work as self-illuminat-

ing pixels in such a big television screen is

a tricky business. But Samsung says it has

found a way of doing this, based on its pro-

duction of semiconductor chips, which re-

quire similar precision.

Samsung reckons that, because micro

leds are made of inorganic materials, they

will last long enough for more than a de-

cade of viewing. This is a dig at oled

screens. There has been some concern that

the organic materials from which these are

formed may deteriorate, shortening the

life of a television which employs them.

This was, indeed, once true. lg, though,

maintains that it is no longer a problem be-

cause the manufacturing process has been

refined using improved materials to make

screens that are more resilient.

The logical end of this shrinkage of

light-generating elements is a screen that

has pixels made from quantum dots. These

are tiny semiconductor particles which, if

excited by light or electricity, glow in a spe-

cific colour that depends on their size.

Larger dots give off light at the red end of

the spectrum. Smaller ones shine blue.

Such dots are already used in some led

televisions as a layer above the backlight,

an arrangement known as qledthat helps

to produce brighter images and also im-

proves contrast. Quantum dots could,

though, at least in theory, be used in the

way micro leds are, as elements of individ-

ual pixels that emit their own light directly

from the screen. It is early days, but Sam-

sung, for one, has been looking at some

sort of hybrid screen which would com-

bine quantum dots with oleds.

Enter the mini

Just to confuse things further, televisions

called mini leds are also hitting the mar-

ket. tcl already makes devices which em-

ploy them, and Samsung and lghave just

launched their own versions.

Mini ledsare not the same as micro

leds. They do not produce an image but

are, rather, used to improve backlighting. A

A

lthough picturequalityhasim-

proved greatly with the development

of flat-screen televisions (see adjacent

article), sound has taken a dive. The

problem is that tvs with slimmed-down

screens have insufficient room for de-

cent speakers to be fitted to them, either

at the back or in the frame. Such televi-

sions are therefore usually connected to

an external sound system, such as a

sound bar or a home-cinema system, to

improve their audio quality.

The loudspeakers of early televisions

were as big as the screen, but engineers

have got good at making speakers small-

er and squeezing them into tighter

spaces. A conventional speaker produces

sound waves using an electromagnet to

vibrate a cone-shaped diaphragm, but

there are other ways to generate sound,

including employing an actuator to

vibrate a flexible panel. That raises the

question, why not vibrate the tvscreen

itself? And this is exactly what a couple

of television-makers are now doing.

Sony, of Japan, was the first to an-

nounce it had developed such a system,

which it calls Acoustic Surface. It is now

fitting this to some of its upmarket tele-

visions. Acoustic Surface employs a pair

of rear-mounted actuators to vibrate a

screen made with organic light-emitting

diodes (oleds). Unlike screens that

employ regular inorganic leds as a back-

light, oleds emit their light directly. This

means oledscreens have few layers—

and that, in turn, means they are easier to

make flexible and are thus able to vibrate

more easily.

This vibration is invisible to the view-

er and, Sony says, does not affect picture

quality. One beneficial consequence is

thata programme’s soundtrack is broad-

cast directly at the viewer instead of from

the side, as is the case with separate

speakers. It is also possible to create

stereo effects by moving the sound’s

point of origin across the screen.

The other version of vibrating-screen

technology now on offer is Cinematic

Sound, from lg, a South Korean firm.

This includes, as one of the screen’s

layers, a 600-micron-thick film that

works as an “exciter” to vibrate the dis-

play. It is all very snazzy. Sceptical au-

diophiles and Luddites will be pleased to

note, though, that both sorts of sound

screens can still be connected to separate

audio systems, if the owner so desires.

In your face

Television audio

Generating sound from the screen