Students, Faculty Work to Create More Efficient Traffic Lights

Students, Faculty Work to Create More Efficient Traffic Lights
Engineering student Tim Schow speaks about the project at the Engineering Projects Symposium on May 18.

Making a difference in the environment can start with something as small as a light bulb.

Five Cal Poly Pomona engineering students, Tim Schow, Scott Borg, Josh Tomashefsky, Ed Sanders and Nathan Son, are working closely with three faculty members to design more energy-efficient lighting electronics for traffic signals using Light Emitting Diodes (LEDs). The research is being conducted with a $74,000 grant from the California Energy Commission.

Standard light bulbs operate directly from the 120 VAC supply present in homes and in older traffic lights. However, the new LEDs operate on voltages ranging from 2 to 5 volts dc. The research focuses on the electronics that will transform the 120 VAC to the lower voltage and utilize negative feedback to control the voltage.

The project will also serve as the students' senior project, a hands-on culmination of their undergraduate experience.

“While the research is on traffic signals, the results can transfer to other LED uses, like billboards and advertising signs,” said faculty member and grant principal investigator Frank Smith, who is working with co-principal investigators professors Phyllis Nelson and Richard Cockrum of the university's electrical and computer engineering department.

The goal of the project is to develop an energy-efficient way to drive the LED lights. Currently large arrarys of LEDs use series or combination series-parallel circuits. A major problem with this circuit topology is that when only one LED light fails, the entire series string fails. This type of failure could be eliminated with a large series resistor, however, the resistor would consume considerable power resulting in a less efficient system.

The students and faculty hope to make the lighting system more efficient by not wasting energy though heat. Feedback control of the energy source is crucial to the success of the research. You might not know that a typical traffic light using an incandescent lamp consumes 170 W of power but an LED traffic light only consumes approximately 12 watts. The research will attempt to reduce the power consumption to less than 10 W.  

“Most lights use half of their energy on just heat,” Borg said. “We want to generate less heat and use that energy to power the light. The trick is to do that while making sure the LED doesn't overheat.”

Research on the project will be completed by Aug. 31. Manufacturers of traffic lights and advertising signs will have free access to the designs developed under the grant by accessing the research results, which will be posted on the California Energy Commission's Web site.