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The technique usually consists of three LCD chips, each one for the red, green and blue components of the video signal. Once the video signal enters into the process, it is decoded and sent to the three LCD chips. Then it is illuminated by an ultra high intensity halogen lamp. This lamp produces an ideal color temperature. The lamp works for thousands of hours and can be easily replaced by the user whenever it burns out and also produces a large amount of light within small area. A broad spectrum of color is split by a prism into three color components. As light passes through the LCD chips, individual pixels can be opened to allow light to pass, or closed to block the light. This process modulates the light and produces the image. This image is then magnified and reflected onto the screen. This image is made of many different shades from each color LCD chip. Other equipments involved in LCD rear projection 1. The Screen - The screen is the place where video image is produced to be seen by the viewer. This screen is different from front video projection or film. It consists of two elements namely Fresnel surface and Lenticular surface. The inner Fresnel surface magnifies and scatters the brightness of the image across the screen. The outer Lenticular surface improves the final shape integrity, contrast and viewing angle of the image. 2. Projection lenses - These are used to magnify the projected image. There may be single lens or an assembly of four to five lenses to maintain shape and brightness of the image and also to handle high temperature variations from both internal and external factors. 3. Mirrors - As the space is considerably small compared to the projection surface where the image has to be projected, a mirror is placed in the path of the projection element, magnifying lenses and the screen. This makes the image larger fro correct view. 4. The Box - It is used to combine all the above elements into a single unit. Advantages - It is compact and portable as LCD chip is very small. One LCD chip is hundred times smaller than three projection tubes used in CRT rear projection. This makes the LCD rear projection TVs lot thinner and lighter than CRT rear projection TVs. - These can save lot of floor space. - Less expensive compared to LCD flat panel or plasma TVs. - Other merits are high contrast and brightness capability and also less power. Disadvantages - Screen door effect - As LCD chip production is expensive, the structure can be complex. - The entire chip has to be replaced if one or more pixels burn out as individual pixels can not be repaired. |