How Do Projectors Work?
It’s all about the light. When you look at an object, it’s because the light is reflecting off of that object and into your eyes. The retina in your eye sends messages to your brain so you can decide what the thing you’re looking at is, whether or not you want to eat it, how far away it is, etc. Our eyes are actually incredibly sophisticated pieces of technology—ever wonder why we only ever see one color at a time, even though pretty much everything around us is full of thousands or millions of different colors? That’s because our retina has three types of color-sensitive cells: red, blue, and green. When you look at something, your brain merges the signals from all three types of cells to form one color that you perceive.
A projector works the same way as your eyes: it sends information about an image into a receptor surface (your eye, your retina), and your brain forms the image you see. A projector does it on a very small scale—it can’t create the entire image out of the light that comes from one spot (because then it would block that spot of light), so instead, it uses a “light modulator” to control the light output pixel-by-pixel. It’s like taking an image made up of thousands or millions of pixels and creating an image made up of hundreds or thousands of tiny dots and controlling the brightness of each one individually. The modulator is a chip with thousands of tiny mirrors on it, which can each be pointed at different angles so that the light they reflect goes into your eyes at slightly different angles—and because your eye is trying to look at the image as a whole, these individual pixels come together to form a specific image.
You’ll notice that some projectors have lenses and some don’t—that’s because sometimes, the light modulator can be positioned so that all of its pixels are aimed at the surface where the actual image is projected (e.g., a wall), which means no lens is necessary. Other times, there isn’t room to position the light modifiers so they can hit the wall directly, but there’s still space to put a lens between them and the wall. Why would you use one projector over another? Size, primarily—you’ll need a lens if your modulator is very close to where you’re projecting on; otherwise, it won’t be able to create a sharp enough image. That’s why the NVIDIA SHIELD Portable projector doesn’t have a lens—the light modulator is right next to where you’d put your wall, so it creates very high-quality images without needing an additional lens.
Why not just use a TV?
A television typically has only one color-sensitive cell, plus a lens to form an image onto the screen. That’s why you can only see one color at a time on your TV—it takes the entire screen and turns it red for one frame of video, green for another frame, and blue for a third frame. This is called “RGB display” because of these three colors.