台大光电所所讯

Powerful LED-based train headlight optimized for energy savings

Professor Guo-Dung J. Su's laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所苏国栋教授

A new LED-based train headlight that uses a tenth of the energy required for headlights using conventional light sources has been designed. If operated 8 hours every day, the electricity savings of the new design would reduce emissions of the greenhouse gas carbon dioxide by about 152 kilograms per year.

Train headlights not only illuminate the tracks ahead, they also play an important role in rail transportation. Because trains are difficult to stop, the headlights must be visible from a distance far enough away to give people or vehicles on the tracks ample time to move out of the way. Traditional train headlights, which use incandescent or halogen bulbs, are bright enough to meet safety regulations but are not very energy efficient because most of the energy powering the light is converted into heat rather than visible light.

We were approached by the engineering and design company Lab H2 Inc., to design locomotive headlights that use LEDs as a light source. In addition to requiring less energy, LEDs also last longer and are smaller and more rugged than traditional light sources.

Fig. 1 new train headlight design uses two half-circular parabolic, or cup-shaped, aluminized reflectors with high-efficiency LEDs placed in the plane where the two reflectors come together. Combining the strong beams from each reflector generates the light intensity necessary to meet safety guidelines. Image Credit: Wei-Lun Liang, National Taiwan University.

Transient carrier trapping effect in organic light-emitting diode

Professor Jiun-Haw Lee

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所李君浩教授

Transient carrier trapping and de-trapping effect in an organic light-emitting diode (OLED) was studied under different voltage waveforms. As shown in Fig. 1 (a), with 1-kHz voltage pulse at 6 V during on-period of 30 μs and different reverse bias (0 V to -14 V) during the off-period (970 μs), the luminance increased with increasing reverse bias up to 36% due to the trapping effect of positive charge at the cathode and the electron transporting layer (ETL), which was proved by the shift of threshold voltage (V_th) in displacement current measurement with different driving waveforms, as shown in Fig. 1 (b).

Fig. 1. (a) Transient luminance responses with different reverse bias under the off-period. (b) Injection trace from -2 V to 4.5 V of displacement current measurement with different waveforms.