How Transmissive Film Works

LCD Basics
The center display of the 3M/Visteon concept BMW uses transmissive film to improve visibility.
The center display of the 3M/Visteon concept BMW uses transmissive film to improve visibility.
Courtesy 3M/Visteon

The acronym LCD is short for liquid crystal display. Liquid crystal refers to a special chemical compound that lies at the heart of this innovative technology. But we'll get to that in a second.

First, let's talk about digital images. Every digital image -- LCD displays included -- is composed of millions of individual pixels, the name for smallest visible unit of the image. On a color LCD display, each pixel is broken down into three subpixels. These subpixels are each assigned a color: red, blue or green. The different colors that you see on an LCD display are produced by controlling the intensity of the light available to each red, green and blue subpixel.

This is where it gets interesting. The way LCD displays control how much light is available to each red, green and blue subpixel is through teeny-tiny particles called twisted nematic phase liquid crystals. Twisted nematics get their name because they are twisted in their natural state. But when you apply an electronic charge to a twisted nematic crystal, it untwists.

What researchers figured out is that they could apply different charges to the twisted nematics to get them to untwist only partially. In an LCD display, each red, green and blue subpixel has its own twisted liquid crystal. If the liquid crystal associated with the red pixel is untwisted all the way, but the blue and green crystals remain closed, then the pixel will show a pure red color. Untwist the blue crystal, and the pixel will now be purple. Untwist all three to varying degrees, and you can create every imaginable color in the spectrum.

Most high-end LCD screens are called transmissive because the light source comes from behind the screen. That light is generated by a small fluorescent tube attached to a light guide that directs the light forward toward the LCD panel.

When the light reaches the LCD panel, it must first pass through a polarizer that aligns the light with the rows of twisted liquid crystals. By charging the crystals, light is only allowed to pass through certain subpixels, setting the color of each of the millions of pixels associated with the digital image.

For more details about the technology behind LCD displays, read our article on How LCDs Work.

So where do transmissive films fit in to all of this? Transmissive films can be applied to the backlight area of the LCD system or the LCD display screen itself to greatly increase the clarity, brightness, security and energy efficiency of the system. Read on to find out more about the different types of transmissive films.