Electronic Displays

When I say "The TV first debuted in -" you say...

"1960?" No, way off.

"1950?" Nope, it was maturing pretty steadily by then.

"1940?" A common answer, but no.

"1930?" It wasn't yet commercialized then, but you're still way off.

"What's the answer, then?" Believe it or not, 1878.

Well, sort of. In 1878, not long after the telephone was invented, the first sketches were drawn of a device used to transmit light over wires. At the time it was called the telephonoscope and was nothing more than a concept of what the future held.

Some of the theory involved in the telephonoscope was used previously in the 1850's with the pantelgraph, but these devices had no display. They were simply capable of scanning small monochromatic flat images (such as hand-written notes) and transmitting them over pre-existing telegraph lines. They were able to scan two images at once (which maxed out at about half the size of regular 8.5x11 printer paper) and a 25 word note took about 108 seconds to scan and transmit.

This is a 1930's mechanical TV made by
 a British company -Baird - after the
technology had finally been refined
 enough to be usable, and shortly
 before the technology became
extinct.The disc's housing is obviously
visible and the screen itself is that tiny
little recessed square on the right.

In 1884, the first actual television was patented by Paul Nipkow, who was 24 at the time. It involved a massive rotating disc with slits cut in it to allow light through. As light was focused on the disc and allowed through the rotating slits, it hit a light-sensitive selenium sensor which reacted to the light by creating electrical signals that were transmitted as slices of frames over wires to a receiving set. Each frame was assembled from the slices on the receiving end by shining a light through another disc rotating at the same speed. The light would activate and deactivate rapidly with the electrical impulses from the first and a very vague image would be displayed. Mechanical TVs never truly caught on, partly due to their massive size (yet small, blurry displays) and the noise they produced. When Nipkow's patent expired 15 years later due to lack of interest, he did not pursue an extension and in fact never returned to the field of television.

What an image on a mechanical TV looked like.

In 1897, the first Cathode Ray Tube (CRT) was developed. CRTs are something that really REALLY stuck around for a long time, as opposed to the ill-fated mechanical television. In fact, CRT televisions are still available to this day at major stores (mostly in the 15 inch and smaller category) but have been disappearing very quickly in recent years. If you've ever heard someone talk about watching the tube, catching Seinfeld on the boob-tube, or something similar, what they're saying is a direct reference to the technology. That"tube" is the cathode ray tube in this type of television. So, how do they work?

Well, there's a reason CRTs are so fat. Remember that old INCREDIBLY heavy television set you or your parents used to have (or in my case, still have?) They were so big because jutting out behind the display was an electron gun. These "guns" literally took a flow of electrons (the electricity from the wall socket) and fired said electrons forward. The electrons were then spread out evenly using electromagnets to bend their path through space. Have you ever seen an old CRT TV stop showing the entire screen and instead display one blindingly bright line or spot right in the center of the screen? That's because the magnet used to spread out the electrons has been disabled.

Once the electrons are all nice and spread out on the screen, nothing happens. If the screen were simply glass the electrons would just go away without spectacle (and waste a butt-load of energy.) What makes it all work is a fluorescent coating on the inside of the screen that reacts to the beam of electrons by glowing. When the electrons are fired in a pre-determined way, they assemble an image on the screen by making the coating glow in different ways at different points on the screen. When the TV isn't plugged into a video source, the electrons are simply fired randomly without order, causing the white noise snowy static we've all come to love.

You may be thinking about today's more popular technologies, specifically the ones involved in flat-screens. Okay, let's talk about those.

LCD monitors and TVs are one of the most popular display technologies on the market today, and run a very wide range of uses. LCD stands for Liquid Crystal Display, and that's exactly what LCDs are. LCD screens involve a back light (sometimes a tube, sometimes a board of small lights or LEDS) and an arry of liquid crystals. The way it works on a pixel-by-pixel basis is that each pixel is made up of three smaller pixels that are red, green, and blue for the primary colors of light. When a pixel is activated and told to display the color white, for instance, it allows all three sub-pixels to just let as much light through from the back light as possible.

The molecules in the screen twist so that the
light can't pass through the polarized filters.

What happens when certain colors are called for is pretty neat, though. Say you want to just show the color blue on the whole screen. In that case all of the blue sub pixels are activated, while all of the green and red sub-pixels are told to switch off. The way they switch off isn't something normal like simply turning off, though...remember the light for this screen comes from behind and doesn't depend on the pixels for anything. Instead what happens is the unused bits twist and bend in on themselves on a microscopic level. This twisting action blocks the light behind the screen from going through, so only blue light is shown because only the blue bits are still untwisted and allowing light through.

The technology is improving immensely but still isn't perfect. SOME light always gets through, which is way an LCD screen showing the color "black" always looks more gray than black when it's turned on versus when it's completely turned off. LCDs are also not just limited to this type of use. Almost every digital watch and hand calculator that's ever existed has used another type of LCD screen that operates on the same principles.

There are many more types of displays, some extinct and some very much alive today, that have existed over the last century. Plasma displays are, very basically, arrays of millions of tiny fluorescent lights sandwiched in glass (the glass is a must, which is why they're heavy) that are turned on with electrical impulses. Plasma screens can be very brilliant, but dim over time, are very susceptible to burn-in (meaning an image can literally be burned into the display if left shown for too long), and they're very power-hungry and heavy.

LED displays are made up of a ton of Light Emitting Diodes arranged in a grid and lit up individually as needed. These are the very same LEDs that make tiny flashlights, indicator lights on coffee makers, cell phones, and the bottom corner of the monitor you're looking at, and on pretty much every other electric device on the planet. Don't confuse these true LED displays (which look really awful up close and are only used for big screens like jumbotrons or marquee tickers) with the so-called LED displays for sale in electronics stores these days. THOSE screens are really just LCD screens with a bunch of white LEDs behind the screen so that the contrast, brightness and lighting can be more easily controlled across the display.

If you're still interested, I encourage you to do some research. As for myself, I'm tired. Hope this helped!