E-paper screens are sunlight-readable, have a wide viewing angle and are ultra-low power making them the ideal display choice for outdoor applications

Virtually every town and city in the world is home to tens, if not hundreds or even thousands of parking meters with digital displays. Some designs haven’t changed for decades, with their simple, traditional numeric liquid crystal displays (LCDs), like those found in pocket calculators. Other manufacturers use back-lit TFT LCDs in their meters – similar to the ones in our laptops and smartphones – to enable them to display richer, more complex information.

But with the maturing of e-paper technology – commonly found in e-book readers such as the Amazon Kindle – there’s now a new and better way to present visual information on these parking meters.

E-paper: Ideal for parking meters

E-paper’s inherent characteristics make it ideal for use in parking meters. Its high resolution means it can display far richer information than the calculator-like LCDs. It’s also much easier to read in bright sunlight than the smartphone-like back-lit variants.

This second point really sets e-paper apart from back-lit TFT LCDs – if you’ve ever had to use a parking meter with this type of display on a sunny day, you’ll probably have had to cup your hands over the screen to try to make out what it’s showing you. From a user experience perspective, there’s room for improvement here.

Where back-lit LCDs rely on a light shining through a layer of liquid crystal, e-paper works very differently. E-paper creates an image on its display using physical ink particles. Ambient light reflects off these, making the content readable. It’s exactly the same principle as printed words on a page or a physical sign board. And it’s what makes e-paper much more user-friendly for outdoor displays, such as those in parking meters.

Ultra-low-power

E-paper’s second big plus is that it requires very little energy to work. There are two main reasons for this: firstly, it doesn’t require a backlight, even at night. So long as there’s a streetlight nearby that’s sufficient to make other words printed on the parking meter legible, your display will also be readable.

Secondly, an e-paper display will only draw on its power source when you change the information it’s showing. Once there, the contents will remain visible, using no further energy (this is thanks to e-paper’s so-called ‘bistable’ characteristic). A smartphone-style back-lit TFT LCD screen, by contrast, requires energy to refresh its contents up to 50 times per second.

Even when you do want to update what’s shown on an e-paper display, the amount of energy required is incredibly low: a full-screen refresh of an e-paper display requires less than 10% of the energy required to refresh a TFT LCD of the same size. And that’s before you introduce e-paper partial update technology, where only a small number of pixels is updated, as opposed to the entire screen. This can slash energy use still further.

Consequently, an e-paper display can easily be run off a battery, which can last for weeks or even months, depending on the number of updates you want to make.

How long the battery in an e-paper-display-enabled parking meter would last will depend on how often the contents of the screen needs refreshing – it could be multiple times per minute in busy locations. But this needn’t mean regular battery changes or the use of mains power: a solar panel, mounted on top of the meter, will easily generate sufficient energy to charge a battery capable of driving the display.

E-paper’s time is now

E-paper has proven itself as a technology in the e-reader world, and is now spreading to other areas. With both small and large quantities of modules readily available from manufacturers like Pervasive Displays, now is the ideal time for parking meter manufacturers to try out the technology in their next generation of products.

Blogger: Scott Soong, CEO, Pervasive Displays