Electronic Readers: Using Lighting For A New Wave of Books

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Electronic readers, more commonly known as E-Readers, have grown in popularity since they give users easy access to a countless number of books. E-books are oftentimes cheaper, more accessible, and better for the environment compared to physical books. E-readers are cheaper than tablets, since they are just used for books. E-books can be read on smartphones and tablets, using apps such as Audible and Libby, but the smaller screen can be difficult to read on, especially in daylight. Because of the lighting technology and materials used, most e-readers can be read in broad daylight and late at night. Electronic readers also have much better battery life than smartphones, due to the low energy usage of the LEDs. 

Electronic readers may not have the computing capacity that smartphones and computers do, but the use of LEDs, light principles, and lightweight materials make them perfect for reading in many situations. 

Lighting Differences between Electronic Readers and Tablets

Liquid Crystal Display (LCD) tablets utilize a backlight for the screens. On the other hand, the Kindle, uses a light guide, which directs light from LEDs on the edges towards the screen. Light from the LEDs enter the light guide. The light is “guided” through by reflecting back and forth until it exits toward the display. The light guide is flat and covers the whole reading screen. Because the Kindle only utilizes four LEDs to light the screen, it is less taxing on the eyes compared to LCD screens which have light shining directly on. The Kindle Paperwhite, a newer e-reader version, has a battery life of 28 hours. The iPhone 11 has less than half that, with about 11 hours from a full charge. 

Electronic Ink

Electronic ink, or “e-ink”, is how the Kindle creates realistic ink on its electronic pages. E-ink is engineered with millions of very small spheres dispersed throughout the entire screen. Each sphere contains white ink, which is positively charged, and black ink, which is negatively charged. Each sphere lies between electrodes. The polarity of the electrodes determines where the white and black ink move towards. The differing polarities between electrodes create the correct black and white spheres, which become a page of a book. A representation of this is shown below.

E-ink, sometimes referred to as E-paper, has many advantages. Electronic readers are popular for many reasons; however, if someone loves the feel of a physical book, e-readers may not be desirable. E-ink creates a realistic feeling page, similar to reading a newspaper. Although the four LEDs allow Kindles to be read even in the dark, the reflective nature of E-paper allows for an even more efficient battery life, since it uses natural light to make the screen visible. 

How Electronic Ink Works. The polarity of the boundaries changes, which cause the spheres to move and produce an image. Photo courtesy of wikipedia

Vision Effects of Electronic Readers 

The issue of screen time has been long discussed, but reading physical books has also been referenced in regard to eye strain. A study in 2013 compared reading a physical book, an electronic reader screen, and an LCD screen, which are shown below. The E-ink screen was an Amazon Kindle, while the LCD screen was a Kindle Fire tablet.  Blinks per second and a rating on a “visual fatigue scale” were recorded. All three methods were tested for 70 minutes. 

The three different reading mediums used in the study. A physical book, an electronic reader, and a tablet (from left to right). Photo courtesy of journals.plos.org

Blinking moisturizes the eye, and a decrease in blinking can lead to dry eye. Dry eye is a common symptom of computer vision syndrome, which occurs with prolonged screen time. Historically, blinking decreases in physical reading, but decreases more when looking at an LCD screen. For the E-ink screen and physical book, the decrease in blinking was similar, while for the LCD screen, blinking decreased significantly more. Blinking was measured with a 30 hertz infrared eye tracking glasses. To keep the amount of light constant, each participant had a digital light meter sensor on their forehead, to guarantee that the total light on the reading surface was 54 lux (flux/area) during each trial. 

To measure visual fatigue, each participant was asked questions such as “I have difficulties seeing” and “I have a headache”. These questions were answered on a 1-10 scale and were asked at the beginning and end of each 70 minute reading session. The scores for these questions before and after reading did not significantly change between reading on the physical book and the E-ink screen. However, high scores were recorded for the LCD screen. Both measurements indicate the LCD screen can lead to eye strain.

Blue Light Emission

Something not discussed in the study above on eye strain is the effect of blue light. Blue light has a higher energy and smaller wavelength than other colors on the visible spectrum. It is theorized that blue light can affect one’s sleep cycle. Natural light emits the full visible spectrum, while also emitting light from the ultraviolet range. Blue light is included in this, however, the exposure to blue light indoors is much more concentrated than being outside during daylight. When the eyes pick up on blue light, the pineal gland suppresses melatonin from being released. The pineal gland is crucial for regulating a human’s circadian rhythm, which makes sure the body rests, is alert, sleeps, etc., at the correct times. When melatonin is suppressed from blue light, the body does not rest at its natural time, causing sleep problems.  

Reading is a relaxing way to end the day; however, if an e-reader emits large amounts of blue light, it may be doing the opposite. The Sony DPT-RP1/B emits no blue light, but it also does not have any backlight or LEDs, meaning it has to be read with another light source on. 

Although blue light may be harmful in large quantities, a blue light emitter can be useful. It can be found here.

A Colorful and Clear Future

From Amazon to Sony, many large tech companies are developing e-readers. Some are trying to replicate physical books and pages, while some aim to provide the ability to read anything, anywhere. For all types of e-readers, a lighting source is needed and a way to transmit the text electronically. The next step for e-readers appears to be colored text, which ClearInk is aiming to do. E-readers are also leading to advances in the note taking industry. E-paper could allow students to use a stylus to take notes. “E-notebooks” would save paper, while giving people the more tactile feel of taking physical notes.