Why We Use…

Fiber-Optic Backlighting

Around for decades, the commuter bus is enjoying a renaissance of positive attention, particularly as gas prices appear to be inching past $2 a gallon this summer, and SUVs are being targeted by religious groups. Perhaps the time has come to exercise the change purse.

Like them or not, the bus does pose a less-expensive alternative for transportation in large cities, when weighed against the cost of gas, maintenance and parking a private vehicle. A 2001 study by the US General Accounting Office showed that a bus rapid transit system, using dedicated bus-only lanes, would incur less cost than a light urban rail system. Appropriately, bus manufacturers and their suppliers are looking for ways to improve their product’s performance and reliability.

North American Bus Industries Inc, Anniston, AL, produces both classic large buses and smaller shuttle vehicles, as might be used in local urban networks or for passenger service at airports. They have also manufactured a 40-ft long composite-bodied bus, which offers improved fuel mileage and lower emissions, along with reducing corrosion issues in cities where roads are salted during the winter. In addition, in February of this year, NABI was awarded a contract by the City of Los Angeles to construct 60-foot low-floor, articulated buses powered by compressed natural gas for the city’s expanding bus rapid transit network.

On one of their transit buses, NABI engineers were dissatisfied with the packaging of several information display panels, so they spoke with sub-contractor Transportation Safety Technologies. The reconfiguration would incorporate several key features, but would increase reliability, ease installation, and simplify service. According to Robert L. LaDow, vice president of product and market development at TST, “Field research pointed to a need to change the backlighting on this panel. We chose to rule out the older lighting technology — incandescent bulbs — in favor of newer designs like electroluminescence and LEDs, both surface mount and fiber optic.”

It was found that EL lighting, in this application, would have problems with connectivity, and with the tendency for the high voltage inverters to fail. “For simplicity, we went to LEDs,” says LaDow. Not a lot of depth was available for the panel, nor was there a continuous linear area that required backlighting. Additionally, one panel at the driver’s station measured 4 ft wide x 8 in. high, while another panel on the center dash measured 16- x 10-in. (A third panel in the engine bay did not require backlighting).

By employing fiber-optic backlighting, TST could stay with LED reliability, but light a panel with 4 or 5 die-cut and standard sizes of fiber optic material. “Each strip has its own LED, and colors can be mixed on a single panel,” LaDow remarks. “The fiber optic strips gave us the consistent and even lighting intensity, without dark spots, that the customer needed.” The low weight of the strips also minimized any damage incurred by vibrations of the bus. Adds LaDow, “We’re already looking at incorporating this material in our standard switch panel lighting line. It’s a better value from a maintenance standpoint.”

The fiber optic technology and support used by TST came from Poly-Optical Products Inc, a division of Lumitex, in Irvine, CA. The company’s products have been used in applications as diverse as underwater pool lighting, medical devices and industrial control panels.

—RM