Improving the color uniformity of multiple colored light-emitting diodes using a periodic microstructure surface.

This study looks at the performance of a periodic microstructure surface on multiple colored light-emitting diodes (LEDs). A periodic microstructure surface on the package was used to reshape the light from the different colored LED chips in the multiple colored LEDs, which decreased the color separation and color nonuniformity of the multiple colored LEDs. Experimental results show that the multiple colored LEDs with a periodic microstructure surface could achieve medium or high collimation as well as good color uniformity. Thus, this study provides a simple and cost-effective method to greatly improve the color uniformity of multiple colored LEDs with medium or high collimation.

Prevalence and dynamic characteristics of generalized joint hypermobility in college students.

BACKGROUND: Generalized joint hypermobility (GJH) is a common, but often ignored, condition characterized by general joint laxity, which is reported to increase one's risk of anterior cruciate ligament (ACL) injury and osteoarthritis. Nevertheless, it is not clearly learned in the prevalence and dynamic characteristics in college students. RESEARCH QUESTION: Is the active motion stability in the six-degree-of-freedom (6DOF) kinematics of the knee joint of people with GJH poorer than that of others? METHODS: This is a cross-sectional study. A population of 489 college students was recruited who was divided into two groups: a GJH group (Beighton score ≥ 4, n = 54) and a normal group (Beighton score < 4, n = 435). A paper questionnaire with questions about the participants' demographic characteristics and musculoskeletal disorder symptoms was collected. A three-dimensional gait analysis system was used to collect the participants' knee joint kinematic parameters during treadmill walking. Variables were evaluated using independent t-tests and Wilcoxon signed-rank tests. RESULTS: The prevalence of GJH was found to be 11.0 % among college students. Participants with GJH exhibited a greater active range of motions in the anterior/posterior translation than the normal (P =  0.026). Participants with GJH exhibited greater flexion at the end of the terminal stance (P = 0.039) and greater anterior translation of the tibia during almost the whole gait period than the normal group (P＜0.05) during the treadmill gait. A greater external angle was found in GJH group during the periods of middle stance (P = 0.008). SIGNIFICANCE: GJH with a prevalence of 11.0 % among college students should be paid attention. Poor active motion stability in anterior/posterior translation may play an important role in the development of knee joint instability, potentially resulting in subsequent ACL deficiency and the development of knee osteoarthritis among people with GJH.

Analysis of position-dependent light extraction of GaN-based LEDs.

The light extraction efficiency of GaN-based LEDs as a function of the position of the light source over the active layer is studied. Several parameters, including chip dimensions, absorption coefficients and package are analyzed on the basis of a Monte-Carlo ray tracing simulation. The light extraction efficiency of a Thin-GaN LED is studied with respect to a sapphire-based LED, including the surface texture.