E paper

What is e-paper?

Electronic paper, e-paper and electronic ink are display technologies which are designed to mimic the appearance of ordinary ink on paper. Unlike conventional backlit flat panel displays which emit light, electronic paper displays reflect light like ordinary paper. Many of the technologies can hold static text and images indefinitely without using electricity, while allowing images to be changed later. Flexible electronic paper uses plastic substrates and plastic electronics for the display backplane.

It is a term that has been used rather loosely for a long time, but broadly speaking it is a display technology that has all the attributes of paper but can be written to and erased electronically. We can list some of these basic attributes as follows:

• High resolution (150dpi or better).
• High contrast, equal to that of print on paper (about 10:1 or better).
• Readable in any ambient light conditions
• Readable at any viewing angle
• Excellent ergonomic features, easy to hold, carry, and use.
• Light weight, at most comparable to an equal sized sheet of card.
• Robust, will withstand being dropped, hit, etc.
• Flexible, or at least bendable.
• Cheap, maybe not as cheap as paper, but easily affordable by everyone.
• Reasonable large area, preferably A4 (298x212mm)
• Bistable, once a display is written it will stay displayed even when power is switched off.

A display that meets all of these attributes can be referred to as an e-paper display suitable for use in an e-publication reader, since it is,in virtually all aspects, an electronic replacement for a sheet of paper. Indeed such display technologies are sometimes referred to as paper replacement technologies.

The importance of readability.

Although the information storage and distribution function of paper is increasingly being replaced by digital technology, paper still holds pre-eminence when it comes to reading that information. By and large most people still prefer to read from a sheet of paper than from a computer screen. Indeed the much heralded 'paperless age' of the personal computer has instead been an age where paper usage has been higher than ever.

The reason for this is that most people do not like reading from a computer screen, either an LCD display on a laptop, or a CRT screen on a desktop. There are several reasons for this, the most important are:

• Low contrast ratio and low resolution lead to eyestrain in long periods of continuous reading off a computer screen.

• The size, and weight of a computer screen means that the reader cannot easily position himself/herself at a proper viewing distance, leading to further eyestrain.

• Computer displays are light generative, or backlit, and often not viewable in a wide range of ambient light conditions or viewing angles, leading to further eyestrain.

• Lack of portability, even with a laptop, limits the times and places in which a document can be read off screen.

• The landscape format of a computer display contrasts to the portrait format of most printed paper documents, resulting in the need for page scrolling of documents that are formatted for print.

Although some people, especially younger computer users, are happy to read from screen for long periods, most users find that the above reasons limit the time that they can comfortably spend reading off screen. Indeed, the problem is sufficiently serious to be recognised by health authorities, and in the UK, the normal fee for eye tests can be waived for computer users.

This means that reading from a screen is usually confined to quick scan reading and searching for information, rather than careful in depth reading. Consequently most will opt for printing out a page that they wish to read carefully.