How do Projectors work
Projectors have special chips which convert the RGB signals in a Digital picture into light beams which are focused on to a screen to show the color pictures. The color in a digital picture, like the video signals transmitted by TV shows, is stored and processed using just 3 colors: Red, Green and Blue, usually written as RGB color.
When the 3 primary colors RGB (Red, Green and Blue) are combined or added together in different proportions, millions of colors can be produced on the TV screen. The image here shows the primary Red, Green and Blue colors and the colors they produce when they are added together. You can see the resulting color in the overlap of the the primary colors in the image here. This process is called Additive color mixing. Red and Green combine to give Yellow color; Green and Blue combine to give Cyan color and adding all three primary RGB colors together gives pure White color.
So White color light has equal quantity of each RGB color: this means pure White light consists of ⅓ of Red, ⅓ Green and ⅓ Blue. If the Blue color light from white light is removed, then the light will have ½ Red and ½ Green with no Blue color in the mix, and this results in a Yellow color light and picture. So by changing the proportion of the RGB colors in the light mix, millions of different shades of colors can be produced. For a projector to convert Video signals to light, the projector has to convert the RGB signals in the TV picture to light beams using individual beams of Red, Green and Blue light and mix the right proportions of RGB light into each pixel of a Video frame.
How 3LCD projector works
Projectors have different means of producing the required RGB light source. Some use a bright white light source and split the white light, using Dichroic mirrors, into individual beams of RGB light.
The image here is the working principle of the 3LCD projector and shows the light path inside a projector. The popular 3LCD projector uses 3 Dichroic mirrors. A Dichroic mirror is a mirror which reflects certain wave length light and let others pass through. In the case of the 3LCD projector, 3 Dichroic mirrors are used, the first reflects Red light but allows Green and Blue light to pass through. The second Dichroic mirror reflects Green but lets Blue light through and the final mirror reflects the Blue light.
Some high end Projectors have Blue Laser beam as the light source to make the RGB light beams. Some have colored LED bulbs to produce the RGB light beam directly and some projectors have a combination of LED and Laser, the so called Hybrid Projector. These different light sources of projectors are explained in detail in a separate page.
A TV picture is made of millions of pixels, for example an HD TV picture is made up of 1920 pixels horizontally and 1080 pixels vertically to make over 2 million pixels or 2 Mega-Pixels. Thus the Projector needs a device to individually process the RGB color of each of the pixels in a TV picture. This Projector Light Processing Unit device is called a ‘Chip’ and today we have 3 types of Chips for projectors: LCD, DLP and LCoS. How each of these Projector light processing units or Chips work, with their advantages and disadvantages are discussed in separate pages. After the individual RGB signals from a Video frame has been processed by the Projector light processing unit or Chip, three individual beams of RGB light comes out of the Projector Chip and these three beams have to be combined into a single beam of light to be projected on to the screen. Prisms are usually used to do this.
After the processed RGB beams are combined into a single beam of light, they pass through a set of lens to focus the Projector beam on to a screen. The lens of a projector plays an important role in the quality of the Projector. The quality of a Projector lens depends on its capability to focus the beam on to the screen from a distance or close-up, change the size of the picture on the screen by Zooming, Shift the picture Up or Down, or Left or Right by a feature called ‘Lens Shift’ and to make corners of the picture exactly 90 degrees by a feature called ‘Keystone Correction. All of these features of the Projector lens are discussed on a separate page.