Freeform optics constitutes a new technology that is currently driving substantial changes in illumination design. It liberates designers and engineers from restrictions of optical surface geometry, enabling them to achieve compact, lightweight, and efficient illumination systems with excellent optical performance. Freeform optics is currently used widely for both fundamental research and practical applications. This Review focuses on the design of freeform illumination optics, which is a key factor in advancing the development of illumination engineering. The design methods of freeform illumination optics can be divided into two groups: zero-´etendue algorithms based on ideal source assumption and design algorithms for extended light sources. The zero-´etendue algorithms include ray mapping method, Monge–Ampere equation method, and supporting quadric method. The algorithms for extended sources include illumination optimization, feedback design, and simultaneous multiple surfaces method. The characteristics and limitations of these design methods are illustrated and a summary of these methods with future outlooks is also given.

Design of Freeform Illumination Optics

A practical method is proposed to design a double freeform surfaces (DFS) lens for LED sources, in order to form uniform illumination in the high distance–height ratio (DHR) lighting system. The ray mapping relationship is first established between the solid angle of the source and the target plane according to the energy conservation law and the variable separation method. A DFS lens is then constructed simultaneously and point by point to the ray mapping based on the Snell's law. Optical performance of the lens is investigated by the Monte Carlo method. A simple and effective method is utilized to optimize the lens design in accordance with the simulation results. As an example, a DFS lens with DHR of 2.5 (distance 30 mm, height 12 mm) is designed by the proposed method. Compared with the traditional methods, the illuminance uniformity is significantly improved from 67.20% to 86.43% and the size of the lens is dramatically reduced.

Double freeform surfaces lens design for LED uniform illumination with high distance–height ratio

We propose a newly projected LED low-beam headlamp based on microlenses. The low-beam headlamp consists of four LEDs, four reflectors, and four microlenses. It does not need a baffle to form the cut-off line. Simulation results show that our proposed low-beam design can satisfy United Nations Economic Commission for Europe vehicle regulations (ECE) R112. The structure of our system is simple and easy to fabricate. Optical efficiency of the system can reach up to 80%, which is much higher than the traditional low-beam lamp design.

Design of a newly projected light-emitting diode low-beam headlamp based on microlenses

A modular of the LED headlamp system based on freeform reflectors is proposed. Glare suppression and optical design are taken into account during the module design. The proposed module consists of six LEDs and each of them has a freeform reflector correspondingly, which is constructed based on the light energy maps and Snell’s Law. Through lighting up different LEDs, the high-beam light and the low-beam light can be switched conveniently. With the proposed method, a module is designed and LUW HWQP LED source whose chip size is 1.0 mm×1.0 mm is adopted for the simulation. Results demonstrate that the lighting distribution can well fulfill the requirements of ECE R112 regulation without any other lenses, shields or baffles. Furthermore, the total optical efficiency can reach up to 80.29% and 81.16% for the low-beam light and high-beam light respectively.

Modular design of a high-efficiency LED headlamp system based on freeform reflectors

https://iopscience.iop.org/article/10.1088/2053-1591/ab79cf/pdf

Investigating optical properties of Cr:GaN system for various Cr concentrations (A DFT + U study)

To eliminate the rainbow phenomenon of white LED sources caused by optical dispersion in a motorcar's headlamp with a thick lens, we propose an LED high-beam headlamp based on free-form microlenses. The free-form microlenses include total reflection surfaces, which collimate the beams emitting from the LED source, and microlens structures, which redistribute the collimated beams to the target plane. We optimize the map relationship between the LED source and the illumination plane according to ECE regulation R112. Simulation and experiment results show that our proposed free-form microlenses could efficiently distribute light radiated from the LED source. All illumination on the test points and zones could reach ECE regulation R112. There is little dispersion in the light pattern in the target plane.

LED high-beam headlamp based on free-form microlenses.

To obtain a prescribed intensity in three-dimensional (3D) rotationally symmetric geometry for an extended source, a two-dimensional (2D) intensity design method is often used. The 3D entity of the lens can be gained by rotating the profile of the lens obtained by the 2D design method. However, the intensity we set in 2D design is quite different from the one we obtain through ray-tracing by the Monte Carlo method in the 3D rotational geometry. Noting the differences of intensity patterns between 2D and 3D, a 3D conversion function (3DCF) should be deduced to convert the prescribed 3D intensity into a 2D intensity in the 2D design process. The extended Lambertian source properties are taken into account during the derivation process. Using the 3DCF, we can quickly obtain the prescribed intensity in 3D rotationally symmetric geometry for an LED extended source without the fussy feedback strategy. The error is small enough for most general illumination. Three examples are presented to demonstrate the correction effectiveness of the proposed conversion function.

Prescribed intensity in 3D rotational geometry for extended sources by using a conversion function in 2D design.

We propose a reflective optics design for an LED motorbike high beam lamp. We set the measuring screen as an elliptical zone and divide it into many small lattices and divide the spatial angle of the LED source into many parts and make relationships between them. According to the conservation law of energy and the Snell’s law, the reflector is generated by freeform optics design method. Then the optical system is simulated by Monte Carlo method using ASAP software. Light pattern of simulation could meet the standard. The high beam headlamp is finally fabricated and assembled into a physical object. Experiment results can fully comply with United Nations Economic Commission for Europe (ECE) vehicle regulations R113 revision 2 (Class C).

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Reflective Optics Design for an LED High Beam Headlamp of Motorbikes

In this paper we propose a projective LED low-beam headlamp of motorbikes. An ellipsoidal reflector is used to collect
light emitting from the LED source. A baffle plate is located in the focal point of the ellipsoidal reflector to form the
cut-off line.Then the light is redistributed by an optical lens. We set the measuring screen as an semi-circular zone and
divide it into many small lattices, divide the spatial angle of the LED source into many parts and make relationships
between them. According to the conservation of energy and Snell law, the lens is generated by freeform optics design
method. Then the optical system is simulated by Monte Carlo method using ASAP software. Light pattern of simulation
could meet the national standard. The low-beam headlamp is finally fabricated and assembled into a physical object.
Experiment results can fully comply with regulations GB5948-1998.

Peng Ge

Papers

LED high-beam headlamp based on free-form microlenses.

Design of a newly projected light-emitting diode low-beam headlamp based on microlenses

Prescribed intensity in 3D rotational geometry for extended sources by using a conversion function in 2D design.

Reflective Optics Design for an LED High Beam Headlamp of Motorbikes

A projective LED low-beam headlamp of motorbikes