How do projectors work?
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Imagine cutting a square hole in a sheet of paper, then holding a torch on one side of the sheet and pointing it at a wall, so that it forms a square of light. Same principal, but instead of a hole in a sheet of paper, it’s a piece of transparent film with the bits around the square being less opaque, or “see-through” than the square part.
Inside the projector, there is a very small, very bright screen with the inverted image to be projected. That light from that screen goes through the lens and is magnified.
The only real difference is that a flashlight uses a mirror and a projector uses a lens. A flashlight is just projecting a blurry image of a lightbulb, but you could pull that image into focus if you could adjust the mirror.
So the obvious part is a really bright light. And it has to be able to project a fairly even amount of light without specific bright center and dim areas like a flash light.
So, how does it project an image? Well, there are a few different methods but I’ll cover the main one I’m familiar with. It uses a spinning color wheel and a specialized image chip. The color wheel spins right in front of the white light. This is done to change the color of the light. This light then shines on the image chip. This chip is covered in numerous tiny mirrors that are controlled with tiny electronics to adjust their angle. Changing the angle reduces or increases the amount of light they reflect. This is what creates the image you see on the screen. From here the light passes through lenses for focusing and adjustments for projection angle relative to the screen.
The projector is really shining a sequence of single color images on the screen, but it does it so rapidly that they combine into a single full color image when you look at them.
*There are some projectors that use 3 image chips instead of one, they use a prism to split the light into colors instead of a color wheel and will display all the colored images at the same time instead of in sequence.
One point others have missed – the light is actually flashing in time with the frames, so each one lines up with the other instead of just a blur were the light constant.
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