LED traffic signal modules as an incandescent lamp alternative

Institute of Transportation Engineers. ITE Journal, Apr 2003 by Iwasaki, Randell H

Procurement of LED modules also led to some innovations in the way the state of California purchases commodities such as LEDs. After the initial purchases of 18,000 modules in 1998 and 1999, Caltrans decided that the traditional purchase process was too cumbersome. As designed, the process could take up to four to six months from the initial decision to purchase to a finalized purchase order. The California Department of General Services-Procurement Division (DGS/PD) had other methods for multiple purchases of large product quantities. With its help, Caltrans was able to set up multiple master purchase agreements with many LED module vendors. This cut the processing time to less than one month from the initial decision to purchase LED signals. In addition, master purchase agreements allowed Caltrans to use total cost of ownership criteria to determine the quantities to be ordered from each vendor. As LED module prices come down, energy costs and other life cycle costs become more important than the initial module price.

Deploying LED modules presented other logistical problems as well, most of which were centered around quality assurance issues. Along with learning about LEDs and the other parts that make up LED traffic signal modules, Caltrans had to learn how to test LED modules and what to test for. Caltrans' position was to ensure that what was put out on the road would work-certificates of compliance were not good enough. With the staggering number of modules foreseen, new equipment and facility upgrades had to be procured for testing on this large number of units.

The engineers and technicians at the Caltrans Transportation Laboratory developed test procedures and equipment needs. A 44-point test was used on both incandescent and LED indications, but the testing of LED modules required that the test be expanded. LEDs, as with any electronic device, respond to different environmental temperatures differently. With an incandescent lamp, there was no need to test at any temperature other than ambient, but temperature can have a dramatic effect on the light output of LEDs. Therefore, 44-point tests needed to be carried out at hot and cold temperatures as well as at room temperature.

The department invested in new test equipment and, most important, a large environmental chamber, which allows Caltrans to test up to 60 LED modules at one time or to test shipments of LED modules as they come in. This investment has proven worthwhile because many manufacturing errors have been discovered. These modules either were replaced or were reworked to meet standards prior to field deployment. This quality assurance effort not only ensures that Caltrans is installing the best material but also helps manufacturers improve their product assembly lines and further improve the quality of material for everyone.

By the time California faced its energy challenge in 2000/2001, Caltrans was putting the final touches on its standards for the remaining configurations of LED signal modules. With Governor Gray Davis' issuance of Executive Order D-1500, Caltrans accelerated the standards approval process and worked with vendors to pre-qualify their products prior to the awarding of master purchase agreements by DGS/PD. By February 2001, state and local governments within California had all the tools necessary to deploy a full spectrum of LED signals.