Commuters in Tokyo are getting a chance to experience some cutting-edge display technology starting on Thursday—although they might have to look hard to see it.

On three commuter trains, some traditional paper advertisements have been replaced with color e-paper displays. The displays, while technologically advanced, proved difficult to read during a demonstration Thursday.

The 13.1-inch displays are made by Hitachi and based on Bridgestone’s "electronic liquid powder" technology. There are two such displays on each of the three trains, mounted on the carriage wall at either end of the train.

Each display is connected to a smaller unit that contains companion electronics and an 8MB memory that can hold 37 advertisements. Each advertisement is shown for two minutes in a continuous cycle.

Electronic paper is still in its infancy. While it has been shown in prototype form for several years, the technology has only recently started making its way into commercial products. One of the highest-profile uses is Sony’s Sony Reader electronic book, but it uses only a monochrome display. Color e-paper development lags.

The displays in the trains offer relatively low resolution, at 50 dpi, and can display only eight colors. There’s also no backlight, so on-screen images appeared quite dark and advertisements utilizing dark colors, such as red and black, were relatively difficult to read. Reflections on the display’s protective plastic cover also caused problems.

The monthlong tests are relatively high-profile because the trains in question run on East Japan Railway’s Yamanote Line, which runs in a loop around the center of Tokyo. It’s used by about 3.5 million people each weekday, making it one of the city’s most important and heavily used railway lines.

The trial will gauge feedback from travelers and see how the system performs in a real-world environment, said Nobuyuki Ogura, a senior manager with Hitachi’s transportation information systems division in Tokyo. They follow a trial last year in which a monochrome e-paper display replaced a wall poster at Tokyo Station, he said.

Hitachi will continue working on the screens and hopes to have a commercial panel ready for use by March 2008, he said.

The Yamanote Line has 52 trains, and on each 11-car train there are 1,414 advertisements, for a total of 73,528 on the entire line. While 96 of the advertisements on each train are LCD displays, the rest must be changed by hand. The use of more digital advertisements would mean new content could be quickly transmitted to each display panel with little fuss.