Apple's Summer-Changing Goal: Helping You See an iPad Screen Through Sunglasses
Ever try to read an LCD display when you're outside and wearing sunglasses? A pair of polarized lenses can make a smartphone, GPS system, music player, or any other screen-based device almost impossible to read. Don't panic, though -- Apple (AAPL) has apparently hit upon a solution, according to a patent application, filed in January, that became public today.
Called "Display That Emits Circularly-Polarized Light," the solution is smart and elegant. At the heart of the problem is polarization. Light normally vibrates in all directions. Polarizing sunglasses only pass through light vibrating in one direction, like a set of grates that keep out anything not oriented the right way. For example, glare off the surface of a pond or lake is actually reflected light that the water surface has polarized into two parts: one vertical and one horizontal. Polarized sunglasses are vertically polarized and cut glare by excluding the horizontally polarized light without equally dimming all the non-polarized light from everything else.
Because LCD screens use so-called linear polarizing technology, they and the glasses can interfere with each other:
The use of portable computing devices outdoors or in other bright environments can result in users viewing such devices through polarized sunglasses, which typically only allow through light with an electric field that vibrates in the vertical direction. Hence, a user looking at the LCD display of a portable device, such as a global positioning satellite (GPS) receiver, portable music player, or personal digital assistant (PDA), may see a distorted image in the display when viewed through polarized sunglasses, due to the polarized filters in the sunglasses blocking the light when the display is viewed from some angles. Depending on the angle at which the device is held or viewed, the image might be clear, completely dark, or somewhere in-between. An image might be further distorted when a lens cover is placed in front of the display for protection or industrial design, because such lens plastics are typically manufactured without good control of optical birefringence, which can result in non-uniform optical retardation. As a result, when viewed through polarized sunglasses, the image may appear to include numerous color- and gray-shade artifacts.Apple's solution is to add to the display a film that converts linearly-polarized light into what is called circularly-polarized light. The circularly polarized light acts as though it has two parts: one that vibrates in one direction and another that vibrates at a 90 degree angle to the first. The result is that the light acts as though it is spinning around an axis, as the illustration below shows:
The now circularly-polarized light doesn't interact with linearly polarized sunglasses the same way the unaltered display image does, drastically reducing any dimming or distortion. What makes the solution elegant is that it's simple, using well-known technology. Not only could Apple build the correcting film into a device, but it could sell one that you could attach to an existing iPhone, iPad, or iPod. All you'll need then is a beach and some sun block.
Illustration: Wikimedia Commons, public domain. Sunglasses: RGBStock.com user lusi, site standard license. iPad image, courtesy Apple.
