3M’s Disappearing Trick

May 18, 2011. How do you make three kilograms disappear from a typical 55-inch LCD panel? 3M is well known for its optical films, so it may be a bit surprising to learn how it can accomplish this trick: get rid of optical films in the LCD panel stack.

The typical edge-lit panel has a reflective bottom layer to recover scattered light, and then a series of layers including a light guide, diffuser, and collimator. In addition, air gaps are required to make the optics work. Building on its experience with multi-layer optical films such as DBEF reflective polarizers, 3M has developed a film that is applied directly to the back of the LCD panel. This film is called “Collimating Multi-layer Optical Film” (CMOF), and is combined with a rear reflective layer separated by an air gap to create the “Air Guide” light mixing system.

One of the benefits of this approach is that it saves material and assembly costs by eliminating all the free-floating films and their required substrates. This leads to secondary advantages such as lower shipping costs.

The technology has many other advantages, however. For example, the standard spacing for LEDs in an edge-light configuration is 12 mm. The reason is the light guides cannot produce a uniform illumination if the LEDs are spaced further apart. 3M has demonstrated the Air Guide technology with LEDs spaced 60 mm apart. This has many implications. For example, designers can now use fewer LEDs with higher brightness, which could help with thermal management. Or they could keep the traditional spacing, and if an LED should fail, it would only make the panel slightly dimmer. This would reduce the need to repair panels under warranty.

The more efficient light mixing also means that designers no longer have to buy the expensive binned white LEDs that everyone else needs for their backlights. Instead, they can use a mix of outliers that are available at much lower cost, and still achieve the same desired color temperature.

This new technology could be a major game changer in LCD panels, eliminating 90% of the light management materials.--Alfred Poor, HDTV Almanac