How do Kindle Screens Work?

The display of a Kindle or e-book reader looks very different from the screens we find on our phones, laptops, or even refrigerators. It is pleasant to the eyes and looks so much like a printed page that sometimes we might even forget that we are not reading a physical book. How do they do that?

The answer is by using paper and ink—but of the electronic kind. Before entering the world of electronic inks, let’s make a quick stop to find out.

Table of Contents

How does ink work?

To make words or images appear on paper, we need paper, obviously, and some ink. Blue, black, or of any color, inks are made up of two major ingredients: a colored substance and a solvent to dissolve the colored substance and keep the ink flowing. The colored substance could be a dye that uses water as its solvent, or a pigment that dissolves in organic solvents like propyl alcohol.

We use devices like printers or pens as vehicles for depositing ink on paper in the form of letters or shapes. Once the solvent from the deposited ink dries up, it leaves millions of tiny colored particles, creating a permanent stain on the paper. And that’s how we get our favorite poems and posters.

But what does this have to do with how a Kindle works?

Electronic inks, or E-inks, also use tiny colored particles suspended in a solvent to make words appear on the screen.

Creating words with charge

For book lovers across the world, very few things beat the feeling of holding a book, be it the crisp vibrant cover of a new mystery novel or the sweet and vanilla odor of an old copy of a fairy tale. These experiences, however, come with their own share of disadvantages.

Like any other physical object, books have weight and take up space. A travel bag stuffed with every book from your summer reading list might end up weighing like a sack of potatoes… not to mention the extra baggage cost if you are traveling by air.

Wouldn’t it be amazing if we could just fit all those books into something light and compact? This aspiration is what led to the invention of electronic ink and paper.

Prototype E-paper Display
Prototype E-paper Display , Credit: Wikimedia/Kuebi

An E-ink display comes together like a sandwich. Instead of bread, the top and bottom layers are two ultra-thin transparent plastic films. These films are then lined with thousands of tiny electrodes that are each the size of a pixel, similar to the pixels in our mobile phones. The filling consists of a suspension of millions of microcapsules floating in an oily substance. These microscopic capsules are the ones that create the magic!

The microcapsules are like tiny golf balls filled with black and white colored particles the diameter of a human hair. The black particles are usually made up of negatively charged carbon black pigment, and the white particles consist of positively charged titanium dioxide (TiO2) pigment. The black pigment forms the ink, whereas the white acts as the paper.

An e-reader display writes by passing an electric current across the top and bottom layers of the “sandwich.” Introducing a charge causes pigments inside the microcapsules to separate and rush towards the opposite charges. This process is known as electrophoresis. A Kindle display uses pixel-sized electrodes to apply positive and negative charges as required.

The working of an electrophoretic E-ink display
The working of an electrophoretic E-ink display, Credit: Wikimedia/Nicolas M

To create a page from a book takes white parts, which act as the paper, and black parts, i.e. the text. Wherever the text should be, the electrodes apply a positive charge to the top layer. This causes the black particles to rush up and the white particles to settle down. And in the areas where we need paper, the exact opposite happens: the electrodes apply a negative charge and the white particles come rushing toward the surface.

To create a grey shade, the electrodes can also bifurcate the charge meaning. This means one side of the pixel has a negative charge and attracts the white particles upwards while the other side does the opposite. This precise control of charges allows a Kindle to create those familiar screensavers.

Kindle Standby Screensaver
Kindle Standby Screensaver, Credit; rawpixel.com/free-public-domain-cc0-photo

After reading about such a complicated procedure some might think: Why do we even need these readers when a laptop or phone does the job?

What’s so special about E-ink displays?

For starters, they don’t strain the eyes as much as mobile phone displays. This is rooted in the fact that E-ink displays have reflective surfaces that are different from the emissive displays of our smartphones and laptops.

Emissive Displays vs. Reflective Displays
Emissive Displays vs. Reflective Displays , Credit: szmaclight.com

We see things when light from the sun or an artificial source like a bulb hits an object, bounces back, and reaches our eyes. The reflective display of a Kindle uses the same phenomenon. It reflects the light coming from an external source towards our eyes, which allows us to read what’s on the display. It does not create its own light like LEDs or LCDs. The displays on our phones or laptops have light-emitting diodes or crystals that emit light when an electrical current is applied to them.

 E-readers with reflective displays also have better visibility in the bright outdoors than emissive screens. Most of us have struggled to read a message or navigate maps when out on a sunny day. This problem arises because the brightness of the sunlight is greater than the light emitted by the display. We often max out the brightness of our device to be able to see clearly. Reflective displays, on the other hand, don’t have to compete with the sunlight. All they have got to do is bounce it back. The brighter the merrier!

E-ink display and LCD under direct sunlight
E-ink display and LCD under direct sunlight , Credit: flickr.com/Tudor Barker

The reflective display is also the reason why a Kindle can run for days on a single charge. Since they don’t have to produce their own light, the only time an e-reader consumes power is during page turns. Once the electrodes have done their job of arranging the particles, they don’t need any more power. So, no worries if you get stuck on a page for a while because you drift off to an imaginary world while reading your novel; your Kindle will have not lost any extra power.

So, dream on, dear reader! Because this amazing technology that causes millions of tiny particles to dance with every page turn was once just a dream in the minds of some MIT undergraduates.

Glossary

Electrodes: Conductors, such as metals, that carry electric current into poorly conducting or non-metallic parts of a circuit.

LCD: Liquid crystal displays are flat panel optical devices that have liquid crystals that manipulate light and produce images by changing directions when a voltage is applied to them.

LED: A light emitting diode is a semiconducting device that produces light when an electric current passes through it.

Pixels: The smallest programmable units that make up a digital image. They come in different shapes, like dots, diamonds, and rectangles.

Flesch Kincaid Grade Level: 7.4

Reading Ease: 70.5

Books of the Future: the Engineering Behind Electronic Ink Displays – USC Viterbi School of Engineering. (2011, June 1). The University of Southern California. https://illumin.usc.edu/books-of-the-future-the-engineering-behind-electronic-ink-displays/

 

Chemistry World. (2003, Feb 28). Ink chemistry. https://www.chemistryworld.com/news/ink-chemistry/3002158.article

 

Tu, C. (2016, May 10). How Electronic Ink Was Invented. Science Friday. https://www.sciencefriday.com/articles/how-electronic-ink-was-invented/

 

LED Screens. (n.d.). Institute of Physics. https://www.iop.org/explore-physics/physics-around-you/technology-our-lives/led-screens

 

Benedetto, S., Drai-Zerbib, V., Pedrotti, M., Tissier, G., & Baccino, T. (2013). E-Readers and Visual Fatigue. PLoS ONE, 8(12), e83676. https://doi.org/10.1371/journal.pone.0083676

Contributors

  • Sanjukta Mondal
    : Author
    Sanjukta Mondal (she/her) has a Master's degree in Industrial Chemistry and loves to explore the world through the lens of chemistry and her trusty camera. During postgraduate research, she worked on the development of functional materials for battery technology and water treatment. Currently, she is trying to navigate through the labyrinth of scientific writing and science writing, fuelled by coffee and her fascination for the extraordinary science and stories hidden behind everyday objects. Writing for SmoreScience will allow her to explore the enthralling world of science and share it with other curious minds.

Copyright @smorescience. All rights reserved. Do not copy, cite, publish, or distribute this content without permission.


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