How projector work

Let’s start from light. So, first a powerful light source emits a beam of intense white light. Then our beam of white  light bounces off a group of mirrors that includes two dichroic mirrors. You know how a prism (or a droplet of water) breaks a beam of light into distinct wavelengths (or a rainbow of colors)? Here is the same thing but through a mirror. So the white light hits the mirrors, and each reflects a beam of colored light through the projector: one red, one green and one blue.

Then, the beams of red, green and blue light each pass through a liquid crystal display composed of thousands of tiny pixels. You can read “ How Liquid Crystal Displays Work”  for a more detailed explanation of LCD technology, but it comes down to tiny, colorless pixels that either block light or allow it to pass through when triggered by an electric current. All three of the LCD screens in the projector display the same image or moving images, only in gray scale. When the colored light passes through these three screens, they relay three versions of the same scene: one tinted red, one tinted green and one tinted blue.

But of course the final image we see isn't red, green or blue; it's full color. So inside the LCD projector, the three tinted versions of this scene recombine in a dichroic prism (a finely crafted combination of four triangular prisms) to form a single image composed of not three colors but millions of colors. You also may know that TV, computers and phones use the same red green or blue colors as projector to show pictures, because these colors emit light, utilizing additive color mixing to create a full spectrum.

https://en.wikipedia.org/wiki/Projector 

https://awolvision.com/blogs/awol-vision-blog/when-were-projectors-invented 

https://electronics.howstuffworks.com/lcd-projectors.htm