# US 2019/0317366 A1 · Freeform optical structures for direct-lit applications

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- Number: US 2019/0317366 A1
- Document ID: US20190317366A1
- Status: Published application
- Kind: A1
- Application number: 16/371,559
- Filed: 2019-04-01
- Published: 2019-10-17
- Earliest claimed: 2018-04-13
- Assignees: Joanneum Research Forschungsgesellschaft mbH
- Applicants: Joanneum Research Forschungsgesellschaft mbH
- Inventors: Christian Sommer; Claude Leiner
- Web page: https://patentgrep.com/patent/US20190317366A1

## CPC

- G02F 1/133611: {including means for improving the brightness uniformity}
- F21V 5/007: {Array of lenses or refractors for a cluster of light sources, e.g. for arrangement of multiple light sources in one plane (combination of two or more refractors F21V5/008)}
- G02F 1/133602: {Direct backlight}
- G02F 1/133606: {including a specially adapted diffusing, scattering or light controlling members}
- F21Y 2115/10: Light-emitting diodes [LED]
- G02F 1/133603: {with LEDs}
- G02F 1/133607: {the light controlling member including light directing or refracting elements, e.g. prisms or lenses}
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- F21V: FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
- F21Y: INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED

## Abstract

An optical apparatus with a distance-to-height ratio, DHR, greater than 2, operable to emit light with a homogenized radiance distribution, the apparatus comprising a plurality of light sources, arranged in an array, a diffusor device at an exit surface of the apparatus, a transparent substrate, arranged between the plurality of light sources and the exit surface, the substrate comprising a plurality of freeform, FF, optical structures wherein the freeform structures are arranged on a bottom side of the transparent substrate facing the light sources.

## Claims

### Claim 1

An optical apparatus with a distance-to-height ratio (DHR) greater than 2, operable to emit light with a homogenized radiance distribution, the apparatus comprising:
a plurality of light sources, arranged in an array;
a diffusor device at an exit surface of the apparatus;
a transparent substrate, arranged between the plurality of light sources and the exit surface, the substrate comprising a plurality of freeform (FF) optical structures wherein the freeform structures are arranged on a bottom side of the transparent substrate facing the light sources.

### Claim 2 (depends on 1)

The apparatus according to claim 1, wherein the freeform optical structures are arranged to define at least one primary irradiance distribution and secondary irradiance distribution on the diffusor device, wherein the at least one primary irradiance distribution is defined by an arrangement of the plurality of light sources and a related first set of FF structures on the substrate, and wherein the secondary irradiance distributions are defined by a periodical arrangement of a second set of FF structures on the substrate in order to achieve a superposition of the secondary irradiance distributions with the at least one primary irradiance distribution.

### Claim 3 (depends on 1)

The apparatus according to claim 1, wherein the superposition of the primary and the secondary irradiance distributions of the FF structures create a homogenized irradiance distribution on the diffusor device.

### Claim 4 (depends on 1)

The apparatus according to claim 1, wherein the arrangement of the plurality of light sources is hexagonal-shaped or square-shaped.

### Claim 5 (depends on 1)

The apparatus according to claim 1, further comprising at least one of: a first spacer component disposed between the array of light sources and the transparent substrate to create a distance between the light sources and the transparent substrate; and, a second spacer component disposed between the transparent substrate and the diffusor device to create a distance between the transparent substrate and the diffusor device.

### Claim 6 (depends on 1)

The apparatus according to claim 1, further comprising a housing, wherein a surface of the housing is light-absorbing.

### Claim 7 (depends on 1)

The apparatus according to claim 1, wherein the transparent substrate forms a plate and consists of polymethyl methacrylate.

### Claim 8

A method for manufacturing flat freeform (FF) micro optical structures for direct-lit applications on a substrate to provide a homogenous irradiance distribution of light on a diffusor device, wherein the light is emitted by a plurality of light sources, the method comprising:
calculating, by an FF algorithm, a geometry of each of the plurality of FF structures on the substrate.

### Claim 9 (depends on 8)

The method of claim 8, further comprising:
simulating a resulting irradiance distribution on the diffusor device;
determining at least one compensation factor based on the simulated distribution and providing the at least one compensation factor to the FF algorithm.

### Claim 10 (depends on 8)

The method of claim 8, wherein the simulation is a ray-tracing simulation, taking into account at least one of the following: a lateral extension of a light source; Fresnel losses on the geometry of the FF structures; intersections of the surfaces of the FF structures; the influence of unguided light rays.

### Claim 11 (depends on 8)

The method of claim 8, wherein the determination of the compensation factor is based on at least one of the intensity maxima and minima of the simulated distribution.

### Claim 12 (depends on 8)

The method of claim 8, wherein calculating the geometry of the FF structures comprises:
determining an upper threshold and a lower threshold of a thickness of the FF structures, the thickness being related to a maximal height of a FF curve;
integrating at least one artificial intersection line into the FF curve when the FF curve drops below the lower threshold;
determining a gradient of the artificial intersection line in dependence of a propagation direction of incoming rays from the light sources and the propagation direction of refracted rays inside the FF-structures to minimize light refracted by the intersection line of the FF curve.

### Claim 13 (depends on 12)

The method of claim 12, further comprising:
determining an intersection point of a base line of the lower threshold with the FF curve, the intersection point being an element of an intersection line;
determining an angle ⊖s representing the gradient of the intersection line;
moving the intersection point towards the upper threshold; creating a construction line using the normal vector of the FF curve in the intersection point;
intersecting the construction line with the intersection line to receive a next point of the FF-curve where the calculation of the FF curve is continued.

### Claim 14 (depends on 8)

The method of claim 8, further comprising:
arranging the FF structures on a side of the substrate facing the light sources.

### Claim 15 (depends on 8)

The method of claim 8, further comprising:
defining at least one primary target area and secondary target areas on the diffusor device, wherein the primary target area is defined by the shape of an arrangement of the plurality of light sources and a related first set of FF structures disposed on the substrate, the first set of FF structures being related to a first irradiance distribution, and wherein the secondary target areas are defined by a periodical arrangement of a second set of FF structures on the substrate, the second set of FF structures being related to a second irradiance distribution; and
superimposing the secondary target areas with the primary target areas in order to join the first and the second irradiance distributions in order to obtain a homogenized irradiance distribution on the diffusor device.

### Claim 16 (depends on 15)

The method of claim 15, wherein the primary target areas have the shape of hexagons or squares and secondary target areas have the shape of equilateral triangles.

### Claim 17 (depends on 8)

The method of claim 8, further comprising:
forming the substrate to obtain the FF structures, using one of the following: laser lithography; laser ablation; a roll-to-roll printing process.