BMW plans to roll out a multicolor head-up display (HUD) on its new 5 Series this spring, and General Motors Corp. said that HUD penetration in its flagship performance car, the Chevrolet Corvette, has climbed from 25 percent in 1999 to 90 percent today. GM said it expects to put the technology in two new vehicle platforms by the 2006 model year. BMW said it will soon launch HUDs in the 6 Series coupe and expects the technology will spread from there.

"Right now, we're launching it in upper- to medium-priced spheres, where the customers are more affluent," noted Martin Birkmann, product advocate for BMW's 5 Series.

"But later on, we expect it to trickle down into less expensive vehicles."

Suppliers said that HUD technology is spreading into other, unnamed automotive programs as well. "We know that it's going into some lower-end luxury vehicles in the 2006 time frame," said Mark Brainard, business development manager for Siemens VDO (Auburn Hills, Mich.), a maker of HUD systems. "We see this technology really taking off and becoming more embedded in the midlevel market segment later in this decade."

Many observers are skeptical of such forecasts, given the lukewarm reception for HUD after its initial launch by General Motors in 1988. But automakers and suppliers are optimistic this time around, because of a combination of better electronics and a renewed understanding of the optics involved in such systems.

"Since the advent of LEDs, we've been able to replace the hot, parabolic overhead-projector-type bulbs with better light sources," said Steven Stringfellow, lead displays engineer at General Motors' Electrical Center (Warren, Mich.). "The new technology has enabled us to take a leap forward and do head-up displays with color and content that we never dreamed of before."

Indeed, besides signaling speed, like the first-generation HUDs, the new models will work in tandem with vehicular global-positioning systems to tell a driver, for example, to turn right at the next intersection. Suppliers and automakers maintain that HUDs will grow even more valuable as next-generation technologies, such as adaptive cruise control and collision avoidance, reach the market in greater numbers. There, HUDs could help save lives, they said, as the "floating displays" use red icons to warn drivers that they are coming too close to the car in front of them.

Adopted from the aerospace industry and installed in the Oldsmobile Cutlass Supreme and Pontiac Grand Prix in 1988, head-up displays were originally intended as a safety feature. The technology, which projects vital information such as vehicle speed about 7 to 8 feet ahead of of the driver, enables users to keep their eyes on the road while they read gauges. According to some estimates, it trims about 1 second from the process of checking the speedometer by eliminating the need to look down at the dashboard, and therefore keeps drivers more aware of what's in front of them.

"We've done studies that show people are much better at detecting events in the forward scene with a head-up display than with a conventional instrument cluster," said Raymond Kiefer, crash-avoidance engineer for GM's Safety Integration Center (Warren).

That, of course, is what automakers also said in the late 1980s and early '90s, when several major manufacturers delved into head-up display technology with limited success.

This time around, however, industry analysts said there is a real sense of renewed interest in HUDs, sparked by a combination of brighter LEDs, better and smaller LCDs and an enhanced knowledge of windshield optics.

"In the past three years, LEDs have grown more powerful, so that they are now bright enough to be used as a backlight on a liquid-crystal display," said Kimberly Allen, director of technology and strategic research for iSuppli/Stanford Resources (Santa Clara, Calif.). "Auto companies are seeing they can use LEDs to solve some of the problems that plagued the [first] systems."

One problem in particular, Allen said, is that past head-up displays used technologies that generated too much heat and were considered toxic because they contained mercury. Some engineers worried, she said, that environmentally friendly technologies would lack the brightness needed for automotive HUDs.

Siemens, however, has solved the problem by replacing fluorescent displays and incandescent bulbs with a package that uses 128 micro-LEDs printed on a silicon base. The LEDs incorporate three colors-red, green and blue-and combine with a 1.6-inch-wide thin-film-transistor display to project information. The TFT display, working with up to four mirrors, operates like a film projector, amplifying the original image and delivering an information box measuring 6 x 3 inches to the windshield.

The image, however, doesn't appear to the driver as if it's on the windshield. "After it bounces off the mirrors and off the windshield, it gives the appearance that it is floating," said Brainard of Siemens.

Siemens engineers said their system offers two key advantages over the original monochrome technologies. The display can combine the three basic colors of the LED to produce as many as 64,000 shades, and it is brighter than its predecessors. The ability to produce colors is important, they said, because it enables automakers to highlight certain safety messages in brighter hues, such as red, that are easily seen under varying conditions.

"There are a lot of losses in the optical system," Brainard said. "So we use an overly intense light source to overcome those losses as the light bounces around."

Siemens also used light sensors in the system to monitor ambient conditions. The sensors work with a software algorithm to modulate the light to match varying conditions. If, for example, a vehicle goes from bright sunlight into a tunnel, the software can quickly turn up the intensity of the display.

Similarly, General Motors has also moved toward LED technology. Even in its monochrome models, the automaker now can use 24 bright-green LEDs to provide greater brightness. The LEDs are combined with a double-layer supertwisted-nematic (DSTN) passive-matrix LCD from Futaba Corp., which gives the HUD better color contrast than earlier models, GM said.

The DSTN technology is said to offer contrast advantages over conventional light-ray-twisting supertwist technologies, because it employs two display layers to counteract the color shifting that occurs in supertwist systems.

GM engineers said that the technology has opened the door to new HUD concepts. "With a high-contrast, high-resolution display, we can do almost any level of graphics right now," Stringfellow said. "We find that these bright-green displays are exceeding 1,000 foot-lamberts [lumens of light per square foot], giving us better contrast with the road."

Stringfellow said that the technology has made the Corvette's HUD reconfigurable as well. By punching a button, drivers can now change the display to project the fuel gauge, oil pressure gauge, tachometer, speedometer or whatever the driver wants to monitor. A similar system also is being used on the 2004 Pontiac Grand Prix.

"It's one of the best products we've ever done," Stringfellow said.

GM engineers said they are also combining their LED-based displays with a newfound knowledge of windshield optics. The company's engineering staff said that it traced many of the early problems, such as distorted images and so-called "ghosting" issues, to the optical properties of the windshields after they noticed that identical HUD systems worked well on some vehicles but not on others.

"It's like a pair of eyes," Stringfellow said. "You have to make sure an eyeglass prescription is right for those eyes. But the prescription of the windshields wasn't right. Each one was different."

Today, the company has improved the optics by placing a polyvinyl butrate film, about the thickness of a plastic garbage bag, between the glass layers of the windshield. The film, GM said, provides better overlap of the images projected.

The company has also improved the optics through an alliance with a Japanese molder of precision plastic mirrors, and has embarked on a program with Nippon Seiki Co. (Nagaoka, Japan) to build the head-up displays.

"The windshield is important because it's the user interface," said Allen of iSuppli/Stanford Resources. "You can talk about low toxicity and all the other advantages, but drivers care most about how it looks when you project the image onto the windshield. If it doesn't look right, they're not going to buy it."

Industry observers said the time could be right for a HUD renaissance, especially as automotive instrument clusters continue to grow more complex. "The market didn't really respond to this technology when it first came out," noted David Cole, executive director of the Center for Automotive Research (Ann Arbor, Mich.). "But it's not unusual for a technology to creep in, go away for awhile, and then come back as a more mature product. That's what happened to the airbag in the 1970s and '80s."

Industry analysts said that the technology is likely to move through the rental-car market, where it would benefit from greater exposure, before it trickles down into mid- and lower-level vehicles. "The price is going to have to come down from the level of a $1,000 add-on, which is where it is now," Allen said. "Until it does, not many consumers are going to consider it."

Both BMW and General Motors are also incorporating navigation information onto the HUD, enabling vehicles to display directions without ever requiring drivers to take their eyes off the road.

"First and foremost, we want this technology to enhance safety," said Brainard of Siemens. "With more and more information overload on drivers, it's going to be more important to reduce the driver's 'glance time.' "

For that reason, GM, which already has HUDs on nine different models, is hoping that success in competing platforms will bolster its own effort. "We want to see BMW pick it up and do a good job with it," Stringfellow said. "If they do, they're going to help to spread the technology."

Whether consumers will embrace the new breed of HUDs, however, is unknown.

"There's definitely renewed interest on the manufacturer's side," said Cole of the Center for Automotive Research. "How customers will receive it is another matter. That's really going to be the final exam."