Design of a bicycle head lamp using an atypical white light-emitting diode with separate dies

To the best of our knowledge, this is the first demonstration of a design for a bicycle head lamp with a high-contrast cutoff line using an atypical white light-emitting diode (LED) with two separate dies. The precise optical model was created by setting the weighting factor on the emitting surface. The downward reflector was designed and fabricated to produce a high-contrast cutoff line in both short-and long-axis orientations, but a yellowish outer pattern was observed. A modified two-color optical model was created to describe the yellowish patterns in both orientations and explain the yellowish effect. Such an effect was caused by the larger coverage area of the phosphor than that by the blue dies. To reduce the yellowish effect near the cutoff line, a specific phosphor area was blocked in the experiment. The yellowish effect was greatly reduced, and the contrast across the cutoff line was enhanced. The presented technology is useful for designing a high-contrast light pattern with such an atypical white LED.