A freeform lens design method based on energy mapping and complementary optimization approaches is proposed to achieve uniform illumination with extended light-emitting diode (LED) sources. This method is primarily derived from a simple source–a target energy mapping approach, while a complementary illuminance on the target plane is introduced to optimize the primary axisymmetric lens so that the profile of the lens can be reformed to produce uniform illumination when applying an extended LED source. By using this optimization method, the illuminance uniformity and optical efficiency of the lens can be improved, respectively, from 0.56 to 0.85 and from 92.4% to 94.3% for an LED light source with chip diameter of 8.9 mm, while the aspect ratio of the lens clear aperture to the source diameter is only 3.8.
As the increase of environment and conservation consciousness in recent years, green-lighting concept begins attracting
much attention of the people in our country; particularly, the exploration of daylight lighting system is an obvious
example. However, in this nature-light lighting system, versatile optical couplers are required to guide and dissipate
sunlight into different indoor spaces to produce assistant illumination, and their coupling efficiencies directly affect the
whole efficiency of the lighting system. Thus, they play an important role in the daylight lighting system. To obtain high
efficient optical couplers, this thesis, other than investigating various used Y-branch couplers, proposes another new type
of coupler, which has a positive- or negative-arc Y-branch structure to split a light-beam into two beams or to combine
two light-beams into one beam with high efficient light output. From optical simulation results, it can be seen that the
output efficiency of this symmetrical Y-branch coupler with positive or negative arc can reach above 90%, no matter it is
used as a combiner or splitter. Furthermore, this thesis also goes through an investigation of the Y-branch output field
distribution and an improved arc design; the coupling efficiency between the coupler and an externally connected optical
fiber can be promoted.
We propose a complementary optimization method to design a freeform lens for uniform illumination with extended
LED sources. With this method, a primary freeform lens is first constructed based on a source-target energy mapping
approach; then a complementary illuminance on the target plane is introduced to optimize the primary freeform lens so
that it can produce uniform illumination with an extended COB LED. The computer simulation results show that the
illuminance uniformity of the optimized lens can be improved nearby 30% as compared with that of the primary lens;
meanwhile, the optical efficiency achieves above 94%.
In many photovoltaic (PV) or sunlight-illumination systems, solar trackers are always essential to obtain high energy/flux concentration efficiency, and that would lead to increase cost and extra power consumption due to the complex structure and heavy weight of the trackers. To decrease the cost while without sacrificing efficiency, a Fresnellens concentrator incorporated with a simple and cheap shutter, which consists of high reflective mirrors instead of conventional trackers, is proposed in this paper to provide solar tracking during the daytime. Thus, the time-variant and slant-incident sunlight rays can be redirected to vertically incident upon the surface of the Fresnel lens by appropriately arranging mirrors and swinging them to the proper slant angles with respect to the orientation of sunlight. The computer simulation results show that power concentration efficiency over 90%, as compared with the efficiency of directly normal incident sunlight, can be achieved with the mirror reflectance of 0.97 and for any solar incident angle within ±75 degrees to the normal of the Fresnel lens. To verify the feasibility and performance of the concentrator with the proposed shutter, a sunlight illumination system based on this novel structure is demonstrated. Both computer simulation and practical measurement results for the prototype of the sunlight illumination system are also given to compare with. The results prove the simple and high efficient shutter applicable to general PV or sunlight-illumination systems for solar tracking.
This paper presents a free-form lens design for indoor illumination. The lens consists of a TIR (total
internal reflection) surface on the sidewall, a refractive surface on the front side, and a concave surface on the
rear side. The TIR surface is decorated with a free-form profile that light rays emitted from the LED with a larger
spread angle to the axis will experience a total internal refection and output from the front refractive surface.
While the central part of the front refractive surface has a convex surface that makes light rays closing to the
optical axis more evenly distributed. The purpose of the rear concave surface is to let light rays emitted from the
LED enter the lens straightforwardly. With this lens light rays from a Lambertian-type LED light source can be
redistributed so that a uniform illumination can be achieved. The optical simulation results show that the
measured optical efficiency is 75% while the uniformity is 80% on a target plane of 6-m diameter and at 2.5-m
A simple approach is presented to design an LED lighting module to provide a uniform illumination. The reflector of the
module is designed using a prescribed candle-power distribution to achieve a uniform illumination on a target surface.
Both the design methodology and the construction of the reflector are stated in detail. The optical efficiency and
uniformity of the module are calculated according to a ray-tracing result. In addition, the effects of the reflector's
aperture and the LED chip size on the optical efficiency and uniformity are also investigated that the result can provide a
reference to LED-luminaire designers and manufacturers.
A freeform collimating lens is designed to project light rays emitted from an LED light source to a far target plane. Generally, the projection distance is assumed to be more than 100 m, and the light beam to have negligible divergence. The lens consists of a total internal reflection (TIR) side surface, a spherical surface in the rear, a vertical plane surface in the outer part of the front, and a freeform refractive surface in the central part of the front. Light rays emitted from the LED source with large spread angles hit the TIR surface and are redirected parallel to the light axis, and those having small spread angles will be collimated by the freeform refractive surface, which is designed with a simple approximation method, and then travel parallel to the light axis. Computer simulation results show that an optical efficiency of 81.5% is achieved under a view angle of ±5 deg and for a 1 mm×1 mm LED source.
A fiber-and-LED-based vehicle headlamp is presented in which light rays emitted from multiple high-power LEDs are gathered using a light collector and then guided into a projector lamp via an optical fiber. This proposed headlamp is intended to reduce the lamp size and the heat-dissipation problem simultaneously. Detailed geometric analysis of the headlamp is given, and the optical efficiency for each component part is also calculated using a TracePro program. The computer simulation results show that the headlamp can produce a legal Economic Commission for Europe low-beam pattern with a total optical efficiency up to 49.4%, and only eight 5-W LEDs (120 lm each) are required.
We present a high-performance cover lens for light-emitting diode (LED) light sources to be applied to large-scale liquid crystal device television (LCD-TV) backlight modules. The cover lens with simple structure can redistribute light rays emitted from an LED light source to make the light distribution more extended so that the luminance uniformity of the backlight module can be increased. To gain a better performance, the parameters of the lens structure are optimized using a genetic algorithm. The simulation result shows that using the cover lens can achieve a luminance uniformity of 94.75% and an optical efficiency of 72.29% for a 46-in LCD-TV backlight module.