STOP UNWANTED REFLECTIONS
Optical bonding is the lamination of the TFT surface to the protective window or touchscreen overlay to eliminate the air gap. Transparent adhesive materials such as silicone, urethane, and epoxy usually couple the display and glass overlay into one optical path that optimally has a single index of refraction.
Also, optical bonding increases the overlay’s durability. The only significant drawback to optical bonding is cost. It is a timeintensive enhancement to standard TFT displays, making it more suitable for devices where bright ambient light viewability or environmental ruggedness is necessary.
Acting as light absorbers, AR treatments consist of multiple layers of thin-film materials deposited on a surface whose arrayed properties cause destructive interference to cancel reflections. The AR coating or a polymer film with AR coating can adhere directly to the surface of the protective window.
Unfortunately, AR-enhanced glass easily smudges, and it is very difficult to clean. AR coatings also wear off through repeat cleanings or touches, so it isn’t a viable contender for touchscreens. These coatings find wider use in avionics applications.
AG surface treatments consist of etching the reflective surface of the display overlay, which results in non-coplanar micro surfaces that scatter reflected light in many directions. While the sum of reflected light is undiminished, the eye then perceives an effective reduction in glare because it senses only the portion of light that reflects collinearly between it and the reflecting micro surfaces.
Overall, AG surfaces are easier to clean and more durable than AR surfaces, making them the best choice for managing external surface reflections in touchscreen applications. AG treatments aren’t the best choice for bright daylight situations, though a mild concoction like AG110 is a good compromise.
FINAL WORD
Products displaying data in bright ambient environments will benefit from optical bonding and reflection-reducing surface treatments. Remember, air gaps and reflective surfaces decrease a display’s legibility, and increasing the backlight output isn’t the best design practice in battery-powered and other applications where power consumption is critical. Reflection management techniques can increase contrast ratios without the additional power necessary for brighter backlights.
Reprints
