E-Paper Technology Explained: Carta, Spectra, Kaleido, and Gallery Compared

What sets e-paper apart from a screen

E-paper, also called E-Ink or electronic paper, isn't a miniature version of a tablet or TV screen, but a fundamentally different technology. Instead of producing light from millions of LEDs, e-paper works with tiny capsules or microcups filled with charged pigment particles. An electric field moves these particles within the capsule to the surface or away from it, making either white, black, or a color visible from outside. The result looks like printed ink on paper: matte, angle-stable light that's reflected from the surroundings rather than emitted by the display itself. That's exactly why e-paper can be read in daylight and bright sun without glare and without backlighting, while an LCD screen loses considerable contrast under the same conditions. For businesses using displays outdoors, in shop windows, or directly on shelves, this readability in natural light is often the first practical reason to look into the technology at all, long before questions of power consumption or color come into play.

The invention of electronic ink

The physical idea behind every Vitria display is older than today's products. It traces back to E Ink Corporation, a company founded on 19 August 1997 in Cambridge, Massachusetts, out of research at the MIT Media Lab. The original idea for an electronic book came from Joseph Jacobson, a professor at the MIT Media Lab, who developed it as early as the beginning of the 1990s during his postdoctoral research, long before tablets or e-readers existed. It was realized together with MIT students JD Albert and Barrett Comiskey, who co-founded the company along with Jerome Rubin and Russ Wilcox. The decisive technical breakthrough came in the early morning hours of 23 January 1997, in a basement lab: Comiskey and Albert placed a single microcapsule between two copper electrodes on a glass slide and demonstrated that an externally applied electric field could move a charged pigment particle inside that capsule in a controlled way. This exact mechanism — an electric field moving a charged particle inside a capsule — remains to this day the physical principle described later in this article as bistability. The reflective, paper-like look described earlier in this article as the difference from a self-illuminating screen is also a direct result of the same experiment: because the moved pigment reflects light instead of generating it, it produces exactly that matte, angle-stable impression of printed ink. What was demonstrated in 1997 on a single glass slide in a basement lab is today exactly the principle behind every Vitria display, whether label, price tag, or signage surface. The difference between that first lab experiment and today's Spectra or Kaleido panel lies not in the physical principle, but in manufacturing: instead of a single capsule on a glass slide, a modern panel contains millions of microscopically small capsules or microcups, each individually addressable via a backplane, plus additional pigment layers for color. The basic principle from the basement lab was industrialized, miniaturized, and extended with color over nearly three decades, but never replaced by a different operating principle. Anyone who orders an e-paper display today technically gets a mass-produced, industrially refined version of exactly that 1997 experiment, not a fundamentally new invention. For a company like Vitria, which deploys these displays in everyday use in Switzerland today, this origin is more than a footnote: it shows that the physical operating principle has been proven and refined in practical use for almost three decades, rather than being a new, untested technology.

Why cold noticeably slows the image refresh

The pigment particles in an e-paper cell don't float in a vacuum, but in a fluid inside the microcapsule or microcup. This fluid is the medium the particles must move through when an electric field pulls them to the surface or pushes them deeper. Like any fluid, this medium becomes more viscous as temperature drops, much like engine oil thickening in winter. The particles then physically move more slowly through the capsule, which has two direct consequences: the image refresh takes longer, and at low temperatures the colors clear less completely during a change, because not all particles reach their target position in time. Both effects intensify as it gets colder. An already-completed image is unaffected, because the bistable particles simply stay put there, regardless of temperature. Only the moment of the change itself is affected — precisely the brief period during which voltage is applied anyway. This isn't a marketing claim, but a physical limit of the technology, just as much a part of e-paper as the bistability described in the next section. It's exactly for this reason that Vitria's standard indoor displays are rated for an operating range of 0 to 40, or 0 to 45, °C, while the separate outdoor product line is built for a considerably wider range of −15 to 65 °C, with correspondingly adapted electronics and sealing (see the article on e-paper for outdoor use). In practice this means: anyone planning a display in an unheated room, a cold storage room, a wintry entryway, or directly outdoors needs the temperature-resistant version, not the standard indoor variant. It is precisely this physics — the more sluggish particle movement in a cold medium — that otherwise leads to a noticeably slower and less complete image refresh, exactly when a display at a cold location most urgently needs to work reliably. It's therefore worth taking a quick look at the actual installation site during product selection, not just the desired display size or color. A seemingly sluggish image change in winter is usually not a defect but exactly this physical behavior, which is why choosing the right temperature class pays off already at the planning stage.

Bistability: why an image stays visible without power

The decisive physical difference is called bistability. Once the pigment particles in an e-paper cell have been moved into position, they stay there, even when no voltage is applied anymore. The display therefore needs no continuous power flow to hold an image, unlike an LCD or OLED screen. A price tag, a signpost, or a menu on e-paper shows its content for days without any energy flowing at all. Only when the content changes is voltage briefly applied to rearrange the particles. This property is why battery-powered e-paper displays last months or years on a single charge, while a tablet with a comparable display area needs to be charged daily. For everyday business operation, this means above all one thing: a display doesn't fail because a battery is empty, but keeps showing its last content stably until the next update is due, no matter how long that takes.

Where power consumption actually occurs

Because a static image costs no energy, the entire power consumption of an e-paper display is concentrated on the moment of the image change itself. When switching, a driver chip must apply an electric field to every single cell, move the pigment particles, and fix the new image. That costs energy for a fraction of a second up to a few seconds, after which consumption drops back to practically zero. In practice this means: a display that changes once a day draws hardly any measurable power over weeks. A display that changes content every minute needs noticeably more. This logic fundamentally sets e-paper apart from LCD or LED screens, whose consumption primarily depends on how long they're switched on, not how often the content changes. This relationship is also why e-paper and battery operation or minimal cabling complement each other so well: the energy balance depends on update frequency, which can be planned and controlled, not on the mere presence of an image on the surface.

The E-Ink platform family at a glance

Most e-paper panels on the market today come from E Ink, the company that brought the technology to market maturity in the 1990s and has since developed several product platforms. These platforms differ not only in the number of colors they can display, but above all in how many pigment layers per pixel physically need to move. The more pigments a pixel contains, the more complex and slower the image refresh. For a company using e-paper, the question is therefore not which platform is fundamentally the best, but which platform fits the use case. A price tag updated several times a day has different requirements than a poster that changes once a week. The following sections walk through the most important platforms in order, from the fastest and simplest to the most color-rich and slowest, to make clear where each one's strengths and limits lie.

Carta: the monochrome base for speed and sharpness

Carta is E Ink's black-and-white platform and, in a sense, the technical foundation the color variants build on. Each cell contains only two particle types, black and white, that move against each other. Because no additional pigment needs to be moved, Carta achieves the highest resolution, the strongest contrast, and the fastest image refresh of all E Ink platforms. For applications where legibility and response speed matter and color plays no role — plain price or text shelf labels, for example — Carta remains the obvious choice. Doing without color here isn't a drawback but a deliberate decision in favor of speed and clarity. Especially on small-format displays, which primarily show numbers and short text anyway, Carta's high contrast directly benefits legibility from a greater distance.

Spectra: black, white, and red for labels

Spectra extends the basic principle with a third pigment: red. Each cell can therefore switch between black, white, and red, which is already sufficient for most retail applications, such as visually highlighting reduced prices or promotions. Because only three instead of two pigments need to move, Spectra is somewhat slower than pure Carta, but still stays within a range that's practical for electronic shelf labels. Spectra is today one of the most widely used color platforms for electronic price tags and shelf labels, because it offers a good compromise of color, speed, and cost for this specific use case. In practice, the single additional color is enough for most price labeling, because red as a signal color already delivers the greatest impact for discounts and promotions, and further shades rarely add much value.

Spectra 3100: a fourth pigment for more flexibility

Spectra 3100 is the natural evolution of Spectra with a fourth pigment, yellow. This allows four colors to be combined directly on a single label, creating additional design options, such as visually distinguishing between the regular price, a reduced price, and a separate note. E Ink also improved refresh time compared with the original Spectra in this generation and widened the usable temperature range for the red and yellow tones, making the platform more practical for environments with fluctuating temperatures, such as chilled shelving. For shelf labels with higher design demands, Spectra 3100 is today often the more obvious choice over the older Spectra generation. For a label, this means concretely: a product can simultaneously show a crossed-out old price, a new price, and a separate symbol or note in different colors, without the surface looking overloaded.

Spectra 6: color for large-format signage

Spectra 6 is a newer, considerably more capable color platform based on a so-called microcup architecture: four pigments, including white plus red, blue, and yellow inks, that mix into up to six visible base colors and, in combination, a color space of several tens of thousands of shades. This color depth makes Spectra 6 suitable for large-format posters, shop-window, and indoor signage where an image needs to convincingly hold its own visually. The price for this is speed: because considerably more pigment layers per cell need to move, a full image change on Spectra 6 takes noticeably longer than on Carta or Spectra, typically in the range of several seconds. For content that changes several times a day, this isn't the right platform; for advertising surfaces and posters that stay up for days or weeks, this speed doesn't matter. Newer waveform methods also reduce the visible flicker during the refresh, but that doesn't change the basic rule that more color depth costs more time per change.

Kaleido 3: a color filter over a monochrome panel

Kaleido 3 takes a different technical approach than Spectra or Gallery. Instead of several color pigments per cell, a thin color-filter layer sits over a classic, high-resolution black-and-white panel. The base panel itself resolves at around 300 PPI; the color-filter layer reduces the effective color resolution to around 150 PPI, at a color space of roughly 4,096 displayable shades. Because the monochrome panel underneath still does most of the work, Kaleido 3's update speed sits considerably closer to pure black-and-white than to the pigment-based color platforms. That makes Kaleido 3 a middle ground: visibly colored, but without the full color depth of Spectra 6 or Gallery 3, in exchange for a response speed that also allows more frequent content changes. For displays combining text and color, such as a card with colored highlights and fine typography, this trade-off of crisp black-and-white rendering with moderate color is often more practical than a pure full-color panel.

Gallery 3: full color directly at every pixel

Gallery 3 pursues the most technically demanding approach, known as ACeP, Advanced Color ePaper. Instead of an applied color-filter layer, every single cell contains four pigments, cyan, magenta, yellow, and white, from which a shade can be mixed directly at the pixel. As a result, Gallery 3 reaches a larger color space than Kaleido 3, with up to around 50,000 displayable colors at a resolution of up to 300 PPI, because no resolution needs to be sacrificed to an additional filter layer. The price for this color depth is speed: because considerably more pigment movements per cell are required than with Kaleido 3, the image refresh on Gallery 3 is slower. Gallery 3 is therefore suited to applications where color fidelity and image quality matter more than update speed, such as high-quality, rarely changing displays. Compared with Spectra 6, the difference lies mainly in the color-mixing principle: Spectra 6 combines preset base colors, while ACeP mixes the color directly at the pixel, allowing for finer gradients, but likewise costing time.

Which platform fits which use case

The common thread running through all E Ink platforms is always the same physical relationship: the more pigment layers per pixel that need to move, the richer the color rendering, but the slower the image refresh. A shelf label that must show a new price several times a day needs speed, so Carta, Spectra, or Spectra 3100. A large-format color display or a poster meant to grab attention and rarely changes can afford the slower but more color-rich Spectra 6 technology. Vitria deliberately applies this mapping within its own product range: Carta, Spectra, and Spectra 3100 for labels and price tags, Spectra 6 for large-format color signage. Choosing a platform is therefore not a question of better or worse, but of fit for the specific use case. Anyone planning an e-paper project should therefore first determine how often the content actually needs to change and how important color is to the specific message, before the choice of platform is even up for discussion.

Frequently asked questions

What's the biggest technical difference between e-paper and an LCD screen?

E-paper holds an image via bistable pigment particles that keep their position without any power supply, while an LCD screen constantly needs energy just to keep an image visible at all. As a result, e-paper draws practically no power at rest.

Why are color displays like Spectra 6 or Gallery 3 slower than black-and-white displays?

Every additional color means an additional pigment that must physically move per pixel. Carta moves only two particle types, Spectra 6 or Gallery 3 four, which slows the image refresh accordingly.

Which platform suits an electronic price tag, and which a poster?

For price tags with frequent changes, Carta, Spectra, or Spectra 3100 are suitable because of their speed. For large-format, rarely changing color signage, Spectra 6 is the better choice, because color depth matters more than speed there.

How many colors can an e-paper display show today?

It depends on the platform: Carta shows only black and white, Spectra and Spectra 3100 three or four base colors respectively, while Kaleido 3 can display around 4,000 and Spectra 6 as well as Gallery 3 several tens of thousands of shades.

How long has the technology behind e-paper existed?

The physical basic principle was demonstrated on 23 January 1997 in a basement lab, a few months before E Ink Corporation was founded on 19 August 1997 in Cambridge, Massachusetts, out of research at the MIT Media Lab. Since then the principle has been industrially refined, but not replaced.

Sources

• E Ink — Spectra 6 (official product page) ↗
• E Ink — Kaleido 3 (official product page) ↗
• IEEE Spectrum — How E Ink Developed Full-Color e-Paper ↗
• Wikipedia — E Ink (company history) ↗