Apple mentioned the ideal pixel density is around 300 PPI, pixels per inch, when they mentioned the specs for iPhone 4/4S and its Retina display, so considering there’s 326 PPI for the Retina display it seems like this is ideal for the human eye. This has led to many phone users wondering why have much more than 300 pixels per inch if the human eye cannot see it?
Reality is a little different according to research we’ve tracked down – according to a number of analysts, and an email Raymond Soneira of DisplayMate Technologies sent back in 2010 to several tech blogs, you will be able to see 477 PPI when holding an iPhone at 12-inches away, and if you moved the iPhone closer to around 8-inches you’ll be able to see up 716 PPI.
This means that the iPhone 5 could theoretically launch with a display at 477 PPI for the maximum your eye will see, and anything more would be too much at 12 inches away, which is the distance a large percentage of people apparently view their phones from. It’s worth pointing out that an iPhone 5 viewed at a closer distance like 8-inches would allow the eye to see up to 716 PPI.
Within the last couple of days we saw LG launch a 5-inch full HD LCD panel, which will be used on future cell phones and features 440 PPI. LG state this is the first full high definition panel in the world for smartphones, so if Apple want to jump above this it seems that there would be no point going past 477 PPI if you hold a phone at 12-inches, or 716 PPI if you hold a phone at 8-inches.
You can see key points below from the email Raymond Soneira sent back in 2010.