Everyone knows real life is nothing like it gear blog picturetelevision —possibly because TV screens are so much smaller than the things we see around us. You couldn’t show life-sized people, cars, sharks, trees, and skyscrapers on a glass-fronted box 30cm (12 inches) high even if you wanted to. But if you’d like your entertainment to feel more realistic, one option is to swap your TV set for a projector that throws giant images of TV pictures onto the wall. Watching TV then becomes more like watching a movie – in the comfort and privacy of your own home. Projection TV is also very useful in business meetings and college lectures where a whole room full of people need to watch a picture at the same time. You can use it to show live TV pictures, video and DVD recordings, or even the output from a computer screen. Let’s take a closer look at the different kinds of TV projector and how they work.
What is projection?
There’s nothing new about projecting images onto a screen. Back in ancient times, Greek philosopher Plato (429–347 BCE) described a famous idea called the “allegory of the cave” in which he likened our everyday experiences to those of a group of cave-bound prisoners watching distorted shadows of puppets flickering on a wall. Thanks to Plato, we can say fairly confidently that people have understood the basic idea of projecting simple images onto screens for thousands of years.
Shadow play like Plato described is something all children enjoy and, simple though it is, it’s the basis for all forms of projection technology, no matter how sophisticated. Think for a moment how it works. You have a light source, you put an image in front of it, and a shadowy image of the object is thrown onto the wall in front of you. If you move the object around, you create an animated image.
Front projection and back projection
There are two basic kinds of projection. If the light is behind you and the screen is in front of you, you make an image through front projection. You can also make projected images a different way. You might have walked down the street at night and seen shadows of people dancing around on their blinds as they walk around inside brightly hit homes. In this case, the light source and the object being projected are behind the screen (the blinds) and you’re looking from the opposite direction in what’s known as back projection.
“Cine” movie projectors, which were developed in 1895 by two French brothers named Auguste and Louis Lumière (1862–1952 and 1864–1948), work by front projection. The projector is positioned behind the audience and throws an image over their heads onto a screen in front of them. Televisions, which became popular a few decades later, work by back projection. You sit in front of the box and watch a pattern of light that’s being created by a very sophisticated electronic mechanism behind the screen.