Transmissive LCD

Transmissive LCD is the first technology to be touted as a viable solution for pico or cell phone projection. In fact, transmissive LCD is widely used today in notebook computers, and LCD TV. LCD stands for liquid crystal on silicon. In this case the backlight, LED, or laser illuminates the display which is made up of liquid crystals. The crystals are aligned in such a way as to block the polarized light that is trying to get past the display. Each pixel is created by an individual crystal. When the display wants to “turn on” a pixel it charges the pixel and the crystal material switches alignment allowing that polarization to pass through and you see the light on the other side. Thus it’s called transmissive.


Several companies are using this approach. The advantages are that this can be simple design. The projector would be made from a light source, probably a red, green, and blue laser or even an RGB LED source. The light source would be collimated by an optic, then the LCD panel, followed by a projection lens for magnification of the image. So right out of the box, this approach is relatively compact, and probably low cost. Transmissive LCD’s are an established technology and the prices for these devices are falling.


The big drawbacks for a cell phone projector are that the projector will need to be very battery efficient. We question whether or not these companies will be able to make an image bright enough with low enough battery power consumption using LCD. Transmissive LCD also has one other big disadvantage. Because the light is pass through the display, there will always be some degree of black spots or “screen door effect" because of the display itself. The microscope wires between each pixel act like the screen material on a screen door when you look through it.


For more information on transmissive LCD see how it works.


See also a definition of LCD.