LIGHTING SUB-ASSEMBLY WITH DUAL MODE OPTICAL ELEMENT

SOUS-ENSEMBLE D`ECLAIRAGE AYANT UN ELEMENT OPTIQUE A DEUX REGIMES

English Abstract

A lighting subassembly and components are provided which increase light output
and uniformity
of brightness and color by use of an optical element that functions
simultaneously as an
outcoupling TIR light guide and a direct throughput lens. It provides typical
benefits of an edgelit
light guide design including shallow depth, extended emitting area, and off
axis light distributions
such as batwing distributions particularly useful in downlighting and other
lighting applications.
Additionally, area dedicated to bezels or edge reflectors can be greatly
reduced or eliminated due
to decreased hotspotting to provide a fixture face with very high percentage
of light emitting area.

Claims

Claims
What is claimed is:
1. A lighting sub-assembly comprising;
a) an optical element having an input face and an output face arranged with
an
input/output alignment angle of less than 90 degrees;
b) a light source which emits light into the input face of the light guide;
wherein a portion of light is directly transmitted from the input face through
the output face
and a portion of light is propagated within the optical element by total
internal reflection at
output face.
2. The lighting sub-assembly of claim 1 wherein the optical element is
further comprised of
an optical element overhang that extends the output face perimeter beyond the
input face.
3. The lighting sub-assembly of claim 1 wherein the optical element is
comprised of a profile
geometry feasible for extrusion.
4. The lighting sub-assembly of claim 1 further comprising a cover lens
through which light
transmits after exiting the output face of the light guide.
5. The lighting sub-assembly of claim 4 wherein the cover lens is comprised
of a profile
geometry that can be extruded.
6. The lighting sub-assembly of claim 1 further comprising a housing that
holds the light
source and optical element in place so light is input into the optical element
input face.
7. The lighting sub-assembly of claim 6 wherein the optical element is
connected to the
housing by means of the optical element overhang.
8. The lighting sub-assembly of claim 6 wherein the housing is comprised of
a profile
geometry feasible for extrusion.
9. The lighting sub-assembly of claim 1 wherein the light source comprises
a light emitting
diode.
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10. The lighting sub-assembly of claim 1 wherein the input face and output
face are not
adjacent surfaces connected by an intersection.
11. The lighting sub-assembly of claim 1 wherein the optical element is
further comprised of
surface features which redirect light.
12. The lighting module of claim 11 in which surface features comprise a
lenticular pattern.
13. The lighting module of claim 12 in which the lenticular pattern
contains a specific extruded
cross-sectional shape comprising a full or partial geometric form of a
polygon, truncated
polygon, concave polygon, convex polygon, parabola, ellipse, sphere, or arc.
14. The lighting module of claim 13 in which surface features comprise a
full or partial
geometric shape of a sphere, paraboloid, ellipsoid, polyhedron, or polyhedron
frustum.
15. A lighting module of claim 11 in which surface features are arranged in
a pattern.
16. The lighting sub-assembly of claim 1 further comprising an opposing
face to the output
face which is not an input face.
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Description

Electronic Filing Date: 7/18/2018
PROVISIONAL PATENT APPLICATION
APPLICANT DOCKET NO: FO-081_R
Lighting sub-assembly with dual mode optical element
RELATED APPLICATIONS
This application claims the benefit of provisional patent application serial
number 62534187 titled
"Lighting Subassembly With Dual Mode Optical Element" filed July 18, 2017.
SUMMARY
A lighting subassembly and components are provided which increase light output
and uniformity
of brightness and color by use of an optical element that functions
simultaneously as an
outcoupling TIR light guide and a direct throughput lens. It provides typical
benefits of an edgelit
light guide design including shallow depth, extended emitting area, and off
axis light distributions
such as batwing distributions particularly useful in downlighting and other
lighting applications.
Additionally, area dedicated to bezels or edge reflectors can be greatly
reduced or eliminated due
to decreased hotspotting to provide a fixture face with very high percentage
of light emitting area.
BACKGROUND
Lighting systems incorporating optical waveguides positioned close to the
light source provide
significant benefits such as thin form factor and adjustable lighting output.
However, efficient
optical coupling from the light source to the waveguide is difficult to
achieve and typically 10% to
30% of light is lost. Traditional approaches that target full edge coupling of
light into optical
waveguides typically lose efficiency by having low utilization of uncoupled
light and of light that
enters the input edge but escapes light guide on a non-output face or near the
edge where the
output is blocked by a bezel or reflector. Often bezels are deemed necessary
to hide "hotspotting",
non-uniform brightness close to light sources due to excessive outcoupling
near the edge. In
addition, light sources such as LEDs often have a variation of their color
output over angle that is
accentuated by coupling into optical light guides.
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Applicant Docket No. FO-081_R
DESCRIPTION
The accompanying drawings are not intended to be drawn to scale. In the
drawings, each identical
or nearly identical component that is illustrated in various figures is
represented by a like numeral.
For purposes of clarity, not every component may be labeled in every drawing.
Embodiment lighting sub-assemblies can be implemented in a wide range of light
fixtures. One
such fixture that benefits from advantages in aesthetic appearance, light
distribution pattern, and
luminous efficacy is shown in Fig. 1 The light fixture 100 is mounted flush
with ceiling tiles 200
in a ceiling in a downlighting application.
For comparison with the embodiment A of Fig. 3, Fig. 2 shows a cross-section
view of a
conventional edge lit lighting fixture. The housing 114 holds in place the LED
board 102 with
LED 101, light guide 103, reflector 108, and cover lens 111. The light guide
103 is a rectangular
shaped sheet with an input face 104 and an output face 105 that are adjacent
faces oriented at a 90
degree angle. Bezels 115A and 115B cover a significant portion of the ends of
the light guide in
order to hold the light guide and cover lens in place and also to mask hot
spot non-uniformities
near the input face of the light guide 103.
Fig. 3A and Fig. 3B show a cross-section view of embodiment A lighting
assembly in which LED
1 light sources are mounted on an LED board 2 which providing a linear light
source that inputs
light into the optical element input face 4. Light propagates within the
optical element 3 and is
emitted from the output face 5. A portion of the light propagates directly
through the optical
element 3 on the direct transmission path 13 while concurrently a portion of
the light propagates
within the optical element on a TIR path 12 until it outcouples from the
optical element 3. Means
for outcoupling light are provided by lenticular surface 9 on the optical
element opposing face 6 as
well as by the light scattering composition of the bulk optical element 3. In
embodiment A the light
scattering composition is provided by polymer beads dispersed within an
acrylic matrix material
having a differing refractive index. Light outcoupling out the opposing face 5
is redirected toward
the optical element output face 5 by the reflector 8.
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Applicant Docket No. FO-081_R
The optical element 3 is comprised of a light transmissive material having a
refractive index
greater than the surrounding ambient environment; in the case of air > 1.
Optionally, regions of
differing refractive index may be dispersed within the volume to scatter light
and cause a portion
of light to out couple from the optical element. Embodiment A is comprised of
PMMA acrylic
matrix with PMMA beads of differing refractive index dispersed throughout the
volume. Other
alternative materials for an optical element include but are not limited to
clear or translucent grades
of polycarbonate, cyclic olefin copolymers, silicone, and glass. PMMA acrylic
has a refractive
index of approximately 1.5 which in air produces a total internal reflection
(TIR) critical angle of
approximately 42 degrees. Dispersed light scattering regions within the
optical element can be
achieved by dispersing materials of differing refractive index throughout the
material.
Alternatively, 2nd phase regions can be formed in-situ during processing of
immiscible material
blends.
The housing 14 encloses and holds in place optical components including the
optical element 3,
LED board 2, and if optionally present, the cover lens 11. The housing
contains a bezel 15 feature
which functions to cover the edge of the optical element including some or all
of the optical
element overhang 7.
The optical element input face 4 is inset from the outer perimeter of the
optical element output face
and is angled so as to form an acute input/output face alignment angle 10, the
angle being 70
degrees in the specific case of embodiment A. The acute input/output alignment
angle functions to
reduce "headlamp" type hot spots from the reflector 8 near the input face 4
and also increases the
ratio of direct transmission to TIR light propagating within the optical
element. The optical
element overhang 7 provides a feature for mechanically securing the optical
element in the housing
14 without excessively trapping light behind the bezel 15 as typically occurs
in a conventional
edge lit construction such as with the bezels 115A and 115B and input face 104
of Fig. 2. This
functions to improve overall efficacy (lumens per watt) of the lighting
system.
The cover lens 11 is an optional component which can be configured to enclose
the output face of
the sub-assembly and provide an appearance more uniform in brightness and
color. Adjustments to
the cover lens 11 surface geometry and bulk light scattering properties can be
used to modify the
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Applicant Docket No. FO-081_R
output light distribution from that originating from the optical element
output face 5. For example,
adjustments to cover lens surface or volumetric light redirecting properties
can be used to decrease
the wide angle degree of lobes in the light distribution pattern or make
brightness or color
variations in the beam pattern emitting from the optical element output face
more uniform. In the
specific case of embodiment A, the surface is congruent with the shape of the
cover lens and the
bulk of the cover lens material has light scattering properties measured to
have a symmetrical full
width half maximum value of 68 when measured as a separate component on
measurement
equipment using as an input light source a narrow beam laser normal to the
input surface.
Fig. 4 is a digital image of a Reference A lighting subassembly representing a
conventional edgelit
light guide construction as shown in Fig. 2 but without a bezel or cover lens.
Fig. 5 is a digital
image of Embodiment A lighting subassembly shown in Fig. 3A and Fig 3B but
without a bezel or
cover lens. Both images were taken at a 45 degree viewing angle of the output
face. Marked on the
images are locations where line scans were analyzed to assess brightness
levels corresponding to
light directly transmitted through the light guide / optical element and light
that does an initial
reflection from the reflector near the input face. In the case Reference A,
the initial reflection
produces significant hot spot patterning commonly referred to as "headlamping"
due to similarity
in appearance of automotive headlamps projecting onto ground in front of a
car. The headlamping
effect is negligible in the Fig. 5 image of embodiment A.
Fig. 6 and Fig. 7 each show graphs and quantitative metrics characterizing
brightness values along
the line scan paths; Fig. 6 for direct transmission and Fig. 7 for initial
reflection. For embodiment
A, the direct transmission is significantly greater than reference A. In
addition to the data of Fig. 6,
this is evidenced by illumination measurements at 45 degrees comparing full
optical light guide
/optical element output vs. that with the output face masked except for the
narrow band of direct
transmission zone near the input edge. In this case, embodiment A direct
transmission was 28% of
full output at 45 degree angle while reference A direct transmission was 12%
of total output at 45
degree angle.
Fig. 8 is a polar plot of embodiment A with one side only LED strip on and the
sub-assembly
oriented down as in a downlighting fixture. The cover lens is embodiment A is
a diffusion lens
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Applicant Docket No. FO-081_R
characterized by a goniometric radiometer as having a symmetric FWHM of 68.
This provides a
large amount of light scattering that decreases the off axis orientation of
light emitted from the
optical element output face and produces a light distribution closer to
lambertian. The amount of
asymmetry in light distribution output can be controlled by selection of
amount of light scattering
in the cover lens to obtain a range of options between the "no cover lens" and
"with cover lens"
options illustrated in Fig. 9.
Fig. 9 is polar plot of embodiment A with LED strips on both sides on and the
sub-assembly
oriented down as in a downlighting fixture and shows a batwing type light
distribution which can
be adjusted to provide less asymmetry by increasing light scattering in the
cover lens. The cover
lens in embodiment A has a symmetric FHWM of 6868 which results in a very
symmetric light
distribution.
List of Numerical References
1&101 LED
2&102 LED board
3&103 Optical element
4&104 Optical element input face
5&105 Optical element output face
6&106 Optical element opposing face
7&107 Optical element overhang
8&108 Reflector
9 Lenticular surface
Input/output face alignment angle
11 &I 11 Cover Lens
12 TIR Path
13 Direct Transmission Path
14&114 Housing
15&115 Bezel
100 Light Fixture
200 Ceiling Tile
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CA 3011689 2018-07-18

Representative Drawing