Is the Kindle actually better for your eyes?

Let’s face it.  We all know someone with the new Amazon Kindle.  On Christmas day 2010, more people activated new Kindles and bought more e-books than at any other time in Amazon’s history.  And why not?  It’s slim, it’s lightweight, and it’s better for your eyes.

Really?  All of my googling yielded a handful of articles claiming that the Kindle is better than the iPad because it’s easier on the eyes, but none addressed the physiological issue of how that could be.  How is it better?  The abundant lack of evidence lead me to do my own research so I could draw a reasonably informed conclusion.  It took more digging than I expected, so rather than waste all that energy on a simple answer, it seemed prudent to share.

Before digging into the answer (skip to the bottom for a basic yes/no), let’s take a moment to review how each technology works.  First, the Kindle.  Kindle screens are created using ‘e-ink’ technology.  Think etch-a-sketch.  Imagine a checkerboard of beach balls.  Each beach ball is filled with ping-pong balls.  For explanation’s sake, let’s simplify further and just take one beach ball full of ping-pong balls.

There are two types of ping-pong balls – black and white.  The black balls carry a positive charge and the white balls carry a negative charge.  The ping-pong balls are just randomly floating around in the beach ball, which is anchored to one square in the checkerboard.  Then BAM.  I hold a negative charge (technically, in the form of an electrode) over the beach ball.  Now, all of the black, positively-charged ping-pong balls are attracted to my new negative charge.  The white ping-pong balls are repelled.  This means that I have a black surface immediately below the place where I apply the negative charge.  THIS means that wherever I apply the negative charge, I get a black beach ball.  So each beach ball effectively becomes a pixel that I can change from black to white simply by applying a positive or negative charge (see image below, adapted from Wikipedia).

The details of how LCD displays work can be found here (, so I won’t go into the minutia.  What’s important to know is that LCD (liquid crystal diode) displays work in a very similar fashion to the e-ink technology I’ve just described.  The difference is that e-ink effectively uses  ambient light.  LCDs, however, do not reflect light.  They require their own light source to be illuminated.  Backlighting is simply a way to provide light to illuminate the various LCDs.  This means you have a wall of LEDs (light emitting diodes) right behind a wall of LCDs (liquid crystal diodes).  LEDs provide the light, LCDs provide the pixellation or pattern of black/white/color.

Here’s what this means for you.  The Kindle only needs to change the pixels.  The iPad and others need to change the pixels AND they need to add light behind so you can see the pixels.  This means that reading an iPad is just like reading a computer screen or watching TV.  Reading on the Kindle is like reading a book.  Books don’t provide the light, you do.  This is why the Kindle is great on the beach – no light source means no glare which means it works well in bright sunlight.  For the same reason, the Kindle is not great if its after bedtime and your spouse is asleep you realize the futility of looking for a flashlight in the dark.

There's no easy diagram for explaining LCD screens, put imagine a matrix of LCDs in different colors (lots of red here) and a wall of LEDs right behind.

So to recap, iPads and other screens use a backlight to illuminate the screen, whereas the Kindle/Nook don’t require it.  The main argument for e-ink, however, is eye strain.  What is eye strain?  It boils down to fatigue brought on by looking at one thing for too long.  Your eyes might get dry, you might find it harder to keep the page in focus, and it might even go as far as to give you a headache.  But you can get eye strain from both devices if you read them for long enough.  One of the major culprits, however, is changing the brightness of the text you are reading.  This requires your pupils to dilate/contract, which takes energy.  Imagine you’re on an iPad reading your book, but then you here the ‘ding!’ that you have a new email.  You quickly switch to your inbox, which leads you to a link, and you browse a bit.  Each web page has different amounts of luminosity (how much light your eye sees), requiring your eyes to do a fair amount of accomodation to the new light levels.  This also contributes to eye strain.  Fortunately (or un- perhaps), this is not a problem for a Kindle that uses only black/white with a set luminance.  You can browse to a webpage, but the luminance stays the same.

In answer to the question of whether the Kindle is actually better for your eyes – I’d say yes, by a slim margin.  Both devices will tire you out if you read for a long time, but the iPad has two downsides in my opinion.  One, if you’re a night reader, this means looking at an illuminated screen when you’re about to sleep which can ultimately keep you awake.  Two, the iPad allows you to browse the web like a computer, and forcing your eye to accomodate to all the different light levels of the various webpages takes its toll.  This is especially the case if you spend all day working at a computer.  So all in all, if you’re in the market for a device that allows you to  just  read books, I’d pick an e-inker.  If you want books and news and email and Angry Birds, clearly the Kindle will not suit your purpose.  But at the end of the day, with all the choices, decisions, and distractions, sometimes it’s nice to come home and pick up a single device for one single purpose.  Then again, you could always skip all this mess and just stick with a good old fashioned book.

Happy reading!

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