Their screen size forces you into several compromises.  This part of our Buyer's Guide explains the implications.

A Buying Guide to iPad and other Tablet Devices :  Part 2 Screen Issues - one of the most important and widely varying factors in different tablet devices
	The amazing Kno tablet, possibly to be released prior to year end, will be available with dual 14.1" screens. This represents perhaps the upper limit of screen size on a tablet.

Perhaps the most most important part of any tablet device's hardware is its screen.

This is the primary output medium for everything it does, and also the primary input medium too.

An awkward tradeoff is required between the 'bigger is always better' screen concept we can embrace when buying a screen for our desktop computer, and the 'tablet devices are convenient, portable, and lightweight' constraints surrounding any tablet.

This part of our iPad/Tablet Buyer's Guide walks you through the different options and implications of screen choices on tablet computers.

Screen Issues

The screen is the main part of a tablet device, something you'll use both for input and output to/from the tablet.  It is possibly also the part of a tablet which currently shows the greatest variation from one product to another, and you need to understand the implications of the different approaches and the compromises inherent in each variation.

Screen size/aspect ratio

Screens are typically measured by quoting the diagonal size of the screen. This used to make sense when all screens were of the same aspect ratio (ie the ratio between the screen's width and height - formerly most commonly 4:3 like an old fashioned television, these days often something around about 16:10 or 16:9 like a new widescreen television) but with differing aspect ratios, the diagonal size alone is no longer so meaningful.

Quick rule of thumb : A wider screen will have a larger diagonal measurement for the same number of square inches of screen that does a 4:3 aspect screen. In other words, wide screens overstate their size when only measured by diagonal.

The range of screen sizes for tablets currently seems to range from a low of about 5" (usually a widescreen format screen) to a high of 9.7" (Apple's current 4:3 ratio iPad screen), although some less well known devices such as the Kno tablet are pushing this number up to somewhat ridiculous sizes - 14.1" and optionally with dual 14.1" screens).

These also probably represent the upper and lower limits for what makes sense in a tablet screen. At 5", you have a small screen that makes it harder to read web pages or to enjoy video; at 10", you have a big screen that unavoidably is starting to become less portable to carry and too heavy to hold.

We'd suggest the sweet-spot is something bigger than 6", and potentially all the way to 9.7" as long as you realize the sacrifices and trade-offs you'll be making if you go to the very large screen size.

Which is better - widescreen or regular aspect ratio screens?

There is no real answer to that, because it depends a lot on your primary uses for the tablet.

If you're mainly going to be using the tablet to watch movies, then you'll probably find a widescreen style screen is better suited.

But if you're going to be using the tablet most of the time to surf the internet, you'll probably find the standard aspect screen is more useful, allowing you to get more of a web page conveniently visible on the screen at a time.

Screen resolution

The other big issue is how many pixels the screen contains.  In general, the more pixels you can get on your screen, the better the quality the image you'll see, allowing you to have smoother letters in small fonts, and higher quality on pictures and video.

There is an upper limit to how many pixels you can benefit from.  Apple sort of determined the limit on how many pixels per inch your eye can conveniently resolve, and claims it to be in the order of about 300 pixels/inch, although this number embodies an assumption about how close to the screen your eyes are.  Their new iPhone 4 boasts 326 pixels/inch (ppi) (ie 960x640 pixels total on the 3.5" display).  In comparison, their iPad has 132 ppi (1024 x 768 pixels on a 9.7" display).  A regular computer monitor will commonly have anywhere from about 70 to 100 ppi.

If two screens are of different sizes, but with the same number of pixels resolution, you won't see more image or detail on the bigger screen, and neither will you see less image or detail on the smaller screen.  Assuming that the smaller screen with the higher pixel density isn't going up above 300 ppi, you'll see as much on the smaller screen as on the bigger screen, and indeed, if the pixel resolution drops much below 75 ppi, the image on the larger screen will start to seem coarse and rough rather than smooth and continuous.

On the other hand, if you have two screens of the same size, but with differing numbers of pixels, you will see more and better information on the screen with the greater number of pixels.  The limiting point here is when things get too small to be clearly seen by the unaided eye at regular viewing distances, no matter how many pixels go into making them up.

One limiting factor on the benefit of more pixels applies to video.  Standard quality video (eg on a DVD) has no more than 720x480 pixels of information per frame.  Most/all tablets already have at least that many pixels, although many cell phones and MP3 players don't, so for regular quality video, you'll get no improvement in picture quality by adding more pixels to the screen.

It is true that HD video can have 720x1280 pixel resolution (for 720p) or even a larger 1080x1920 pixel resolution (for 1080p and 1080i) and in such cases, obviously more pixels up to these maximums will allow for more picture information to be shown and the quality to therefore improve.

But you will probably never choose to watch true High Definition video on your tablet, no matter what the advertising might suggest.  Why?  Because it will use up way too much storage.  A good quality video might use about 1GB per hour of programming, but a true high quality video can go up to (and over) 10GB per hour.

That is fine when you're watching video from a Blu-ray disc with a 50GB capacity, and where you have a library of discs on your bookshelf stretching several feet, but when you have a 32GB iPad (that also lacks sufficient pixels to display the image correctly anyway) you'd end up with only enough storage for a single movie to be on the unit at a time - not much use if you're on a 10 hour plane ride.

In other words, and to try and tie these issues together, more pixels are nearly always better than fewer pixels, and it is usually preferable to have more pixels on a same size screen than a bigger screen with the same pixels.

Don't accept any tablet with less than 800x480 resolution, and try and hold out for something larger than this.

Visibility in bright light

This is the Achilles heel of many LCD screen devices.  In bright sunlight, they 'wash out' and it gets very hard to see whatever is on the screen.

Some screen technologies are better than others in terms of displaying a clear image in bright sunlight.  If you expect to be using your tablet outdoors in places with bright sunlight, you should factor this into your calculation.

Part of a multi part Buyers Guide to iPad/tablet devices.  Please visit the other parts of this series - links at the top right.

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Originally published 30 Sep 2010, last update 21 Jul 2020

You may freely reproduce or distribute this article for noncommercial purposes as long as you give credit to me as original writer.