Why light from TV’s display doesn’t project it’s image on surfaces like projector?


Why light from TV’s display doesn’t project it’s image on surfaces like projector?

In: Physics

A projector sends light rays in such a way that light corresponding to a single pixel only goes in the direction where that pixel would be on the surface. So, each point of the surface is only lit with the light from one pixel allowing you to see the projected image.

A display has all pixels shining in every direction. This means that any point of the surface will be lit by the light from all pixels, that doesn’t produce an image but allows you (when the said surface is your eye) to see entire image on the monitor.

The light bulb in a projector is way more powerful than the individual pixels that make up an LCD or OLED screen. It shines through the imaging chip, picking up the colors and image and hits a lens, which concentrates it further into a coherent beam of light. Then the light travels a few feet and hits the wall, or screen. As it travels from the lens it will spread out and become less coherent, losing its luminescence, or brightness. The further it goes the larger it gets but also the less focused and bright.

The same thing actually happens with light from pixels but since it’s much less bright it loses coherence that much faster. And since there’s no lenses to focus the light it spreads out in every direction. But it’s mainly the combination of very powerful light bulb and a lens to focus the image that allows us s to project a detailed image onto a surface.

TVs are designed to have a wide viewing angle. To do this each pixel is intentionally diffuse so that it can be seen from multiple angles. Otherwise you would have to sit at a very specific place in front of the TV to see anything and even then it would only be the small part of the screen corresponding to your eye.

Short answer: projectors shoot light in straight lines, tv screens shoot light in all directions.

Each pixel of a tv screen sends its color of light in every direction at once, like a light bulb. You can see the image when you look at the tv screen because light from each pixel is hitting your eye from exactly one direction, but nearby surfaces like a wall are being hit by light from each of the pixels individually. When the light is reflected off the wall and hits your eye, the different colors of light are scattered across the wall and the image has been destroyed. If you have a tv on in a dark room, you’ll still be able to see the intensity and the overall color of whatever is playing reflected on the surroundings, but you won’t be able to make out any detail.

I don’t know exactly how a modern projector works, but somehow they shine light from each pixel in only one direction. This allows the image to be cast onto a surface without any blurring.

All that’s needed for a projected image is for the light hitting each point on the viewing surface to be coming from only one direction. If you placed a barrier in your room with a tiny hole in it and had a very bright tv, you could create a projection on the wall opposite the tv by forcing the light from each pixel to pass through the hole- but because the light from pixels on the bottom of the screen will have to slant upwards to reach the hold, the image will be upside-down!

This phenomenon is called a camera obscura and they are SO. COOL. Google it and look at pictures!

It’s all about focus. A TV does project light at a wall but it’s unfocused so we only see a color average. This is because the light from a TV is going in all directions from each pixel. In a projector the light goes through a lens designed to bend light so that each pixel is sent in a straight focused line.