Yi-Chien Lo

Analysis of the far-field region of LEDs.

Versatility in the design of optical systems is one of the key features of light-emitting diodes (LEDs) that has attracted considerable attention. In the analysis of systems using LEDs, it is useful to know if the distance is far enough from the LED to allow the radiation pattern to be simulated by the point source approach. We propose three far-zone conditions for LED light modeling: the far-field distance, and for practical purposes the quasi far-field and minimum far-field distances. Different types of LEDs have different far-field ranges. We analyze these differences by modulating key parameters like geometrical structure of encapsulating lens, chip size, chip shape, chip position, and package errors. We find that far-field region considerably depends more on the shape of both lens and chip than all other parameters.

Collimating lamp with well color mixing of red/green/blue LEDs

A novel light luminaire is proposed and experimentally analyzed, which efficiently mixes and projects the tunable light from red, green and blue (RGB) light-emitting diodes (LEDs). Simultaneous light collimation and color mixing is a challenging task because most collimators separate colors, and most color mixers spread the light beam. Our method is simple and compact; it only uses a short light pipe, a thin diffuser, and a total internal reflection lens. We performed an experimental study to find a balance between optical efficiency and color uniformity by changing light recycling and color mixing.

Precise Spatial-Color Optical Modeling in Phosphor-Converted White LEDs

White light LEDs are playing a more and more important role in display in various structures. Here, a new modeling algorithm is proposed for use in phosphor-converted white light-emitting diodes (pcW-LEDs); the algorithm can be used to accurately simulate color appearances, potentially enabling optical designers to remove yellowish/bluish spots in LED lighting. The proposed modeling method was applied to simulate a pcW-LED without an encapsulation lens, and subsequently, a pcW-LED with a hemispherical lens. Both simulations accurately predicted the blue and yellow light distribution. The model was further verified by applying a total internal reflector lens to the pcW-LED. In the midfield region, the blue and yellow light distribution exhibited large variations as the observation distance changed; this varying light pattern for both the blue and yellow lights can be accurately predicted using the proposed model. The developed optical model should facilitate designing a pcW-LED that features high-quality illumination and increased color uniformity.

Side-illuminating LED luminaires with accurate projection in high uniformity and high optical utilization factor for large-area field illumination

A novel light luminaire is proposed and experimentally analyzed, which accurately projects light into a large rectangular area to achieve uniform illumination and a high optical utilization factor at the target. Side-illuminating luminaires for large-scale illuminated area are typically set with an elevated tilt angle to enlarge the illuminated area. However, the light pattern is bent thereby reducing the uniformity and optical utilization factor at the target. In this paper, we propose an efficient and useful approach with a rotationally symmetric projection lens that is trimmed to adjust the bending effect and to form a rectangular illumination light pattern on the ground. The design concept is demonstrated and verified. Several potential applications such as highly uniform illumination with fitting shapes for sport courts are analyzed and discussed.

Optical design of the focal adjustable flashlight based on a power white-LED

In the paper, we design a focal adjustable flashlight, which can provide the spotlight and the wide-angle illumination in different modes. For most users, they two request two illumination modes. In such two modes, one is high density energy of the light pattern and the other is the uniform light pattern in a wide view field. In designing the focal adjustable flashlight, we first build a precise optical model for the high-power LED produced by CREE Inc. in mid-field verification to make sure the accuracy of our simulation. Typically, the lens is useful to be the key component of the adjustable flashlight, but the optical efficiency is low. Here, we introduce a concept of so-called total internal refraction (TIR) lens into the design of flashlight. By defocusing the TIR lens, the flashlight can quickly change the beam size and energy density to various applications. We design two segments of the side of the TIR lens so that they can be applied to the two modes, and the flashlight provides a high optical efficiency for each mode. The illuminance of the center of light pattern at a distance of 2 m from the lamp is also higher than using the lens in the spotlight and wide-angle illumination. It provides good lighting functions for users.

Optical modeling with precise spatial-chromatic light distribution in phosphor-converted white LEDs

White light LEDs become more and more important in display and lighting in various structures. Here a new modeling algorithm for phosphor-converted white light-emitting diodes (pcW-LEDs) is proposed, aiming to perform accurate simulation for color appearance, where potentially enabling optical designers to remove yellowish/bluish spots in LED lighting. The proposed modeling method is applied to simulate a pcW-LED with a hemi spherical lens. The simulation accurately predicts the blue and yellow light distribution. The model is further verified by applying a total internal reflector lens to the pcW-LED. In the midfield region, the blue and yellow light distribution exhibit large variations as the observation distance changed; this varying light pattern for both the blue and yellow lights can be accurately predicted by using the proposed model. The well-established optical model should facilitate designing a pcW-LED that features high-quality illumination and enhances color uniformity.

High-performance LED luminaire for sports hall

In this paper, we present a luminaire design with anti-glare and energy-saving effects for sports hall. Compared with traditional lamps using in a badminton court, the average illuminance on the ground of the proposed LED luminaire is enhanced about 300%. Besides, the uniformity is obviously enhanced and improved. The switch-on speed of lighting in sports hall is greatly reduced from 5-10 minutes to 1 second. The simulation analysis and the corresponding experiment results are demonstrated.

Optical Design of Bicycle Head Lamp for K-mark Regulation Based on White LEDs

In this research, we designed a bicycle headlamp to meet the K-mark regulation using a high-power white LED. A prototype performed a contrast of 42 across the cut-off line and a special lighting pattern for roadway illumination.