While the iPad 2 and the iPhone 4 share a lot of the same DNA, there has been some debate as to how the tablet’s LCD screen holds up against its handheld sibling -- particularly regarding a small gap of air between the glass and the LCD panel itself. DisplayMate Technologies to the rescue!
We recently reported on DisplayMate Technologies’ comparison of the iPad 2 display against the presumably higher-resolution iPhone 4 Retina Display, where researcher Dr. Raymond Soneira revealed that the larger iPad 2 display actually held up quite well against the iPhone 4.
Now, DisplayMate is back with new research on the subject of an air gap found in the iPad 2 between the cover glass and LCD panel. As you may recall, for the iPhone 4, Apple bonded these two critical elements together to make the screen appear to be sitting right on the surface of the glass. So how does the iPad 2 compare?
“We measured the iPad 2 screen reflections from light that is coming from all directions -- this is called diffuse illumination,” Dr. Soneira reveals on the DisplayMate website. “Next we examine mirror (specular) reflections off the screen of the iPad 2 and also the iPhone 4 for comparison. Mirror reflections can be visually annoying because they produce image content that competes with the LCD and your eye attempts to focus on them as well. Because the screens are made up of multiple layers of glass and plastic they actually produce multiple reflections from light reflecting off the different layers.”
Dr. Soneira and his team used a pencil-sized beam of light to show the effects of the air gap with the iPad 2 display. As you can see from the images here, the beam of light creates only one prominent reflection on the iPhone 4, the result of directly bonding the cover glass and LCD. The image on the left shows the iPad 2, with two prominent reflections due to the air gap between these critical elements.
“We examined this by bouncing a tiny 3mm in diameter collimated pencil beam of light at 45 degrees to the screen and photographing the reflected beam of light with a Nikon D90 DSLR camera,” Dr. Soneira elaborates. “Highly magnified photos are shown in Figure 2 -- the circles are all 3mm in diameter. The iPad 2 has an air gap between the cover glass and LCD panel so there are 2 prominent reflections from them. A weaker 3rd reflection from the bottom of the cover glass can also be seen between them. On the iPhone 4 the cover glass and LCD panel are optically bonded together to reduce multiple reflections. This also results in the LCD image appearing much closer to the surface of the cover glass. The bonding produces a drawn out haze reflection.”
Judging from these tests, DisplayMate has made an “educated guess” that the air gap on the iPad 2 display is about 0.65mm thick, while the cover glass itself is 1mm thick. “The total specular reflection from all layers is about 3.5 percent on both the iPad 2 and iPhone 4,” Dr. Soneira reveals.
So why did Apple choose to use an air gap on the iPad 2 display rather than the direct bonding used by the iPhone 4? The answer comes down to size -- and money.
“[The iPad 2] is much larger than the iPhone 4 and it’s much harder to properly bond two large pieces of glass together,” Dr. Soneira summarizes. “It’s also much less expensive to replace just the broken cover glass instead of the entire assembly that includes the bonded LCD panel, as with the iPhone 4. While it’s possible for dust to get inside the air gap, that could be a problem only if the screen needs to be repaired -- the factory assembled units should be fine.”
For a complete and detailed look at the iPad 2 display, visit DisplayMate’s website, where you can also get a look at the company’s research on the iPhone 4 and iPhone 3GS LCD display.
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(Image courtesy of DisplayMate Technologies Corporation)
