WO2011002661A1

WO2011002661A1 - Lighting assembly

Info

Publication number: WO2011002661A1
Application number: PCT/US2010/039820
Authority: WO
Inventors: Michael A. Meis; Billy L. Weaver; Karl M. Kropp
Original assignee: 3M Innovative Properties Company
Priority date: 2009-06-29
Filing date: 2010-06-24
Publication date: 2011-01-06

Abstract

Lighting assembly comprising: an enclosure having an interior surface and a first transmissive area, the interior surface comprising a first surface area region and a second surface area region generally opposite the first surface area region, wherein the first transmissive area is within first surface area region, and wherein the second surface area region includes a surface area generally opposite the first transmissive area that is at least one of semi-specularly reflective or diffusely reflective and has an on-axis average reflectivity of at least 90% for visible light of any polarization, and the remainder of the interior surface area has an on-axis average reflectivity of at least 98% for visible light of any polarization; a light guide disposed within the enclosure and between the first and second surface area regions, including substantially between the first transmissive area and the surface area generally opposite the first transmissive area that is at least one of semi-specularly reflective or diffusely reflective, the light guide including a first opening for receiving light, wherein the first opening does not extend between the first transmissive area and the surface area generally opposite the first transmissive area that is at least one of semi-specularly reflective or diffusely reflective; and a first light source positioned to introduce light into at least the first opening of the light guide.

Description

LIGHTING ASSEMBLY

Background

[0001] Light emitting diodes ("LEDs") (also sometimes referred to as "solid state lamps"), including those having Lambertian light emission pattern and having a light emission collimated to a range from 20° to 30° in at least one direction (e.g., the thickness direction of an enclosure, as well as in a cone), are well known in the art. One limitation of lighting with LEDs is providing uniform illumination over an output surface. The ratio between the size of the LED die and illuminated area typically ranges from several 100 to several 1,000 to 1, to even more than 10000 to 1 (i.e., size of the lighted area vs. the size of the LED die). One technique for trying to obtain more uniform lighting from LEDs is to utilize numerous, relatively closely spaced LEDs, which is an approach that is inefficient from both a cost standpoint having to use numerous LEDS, as well as the sensitivity of these systems to drift or failure of an individual LED.

[0002] LEDs are used in a variety of applications. Distributing light from LEDs is a common need shared by signs, displays, and liquid crystal displays. Here, a light distribution enclosure is placed behind an element which can be a colored panel, a graphic, or an LCD panel. Often, the goal is to achieve uniform illumination in a thin form factor, and with the fewest possible light sources.

[0003] LEDs have been used to light vehicle sill plates, but tend to lack desired efficiency, brightness, and uniformity. Current lighted sill plate designs can use multiple LEDs directly coupled to a light distribution assembly. Generally this is a sheet of clear plastic, but it could also be a bundle of plastic optical fibers. Typically these approaches lack lighting uniformity, sufficient brightness, or both.

[0004] One approach to try to provide a more efficient distribution of light is to use multiple LEDs directly attached to the edge of a light guide.

Summary

[0005] In one aspect, the present disclosure describes a lighting assembly comprising: an enclosure having an interior surface and a first transmissive area, the interior surface comprising a first surface area region and a second surface area region disposed generally opposite the first surface area region, the first transmissive area being within the first surface area region, the second surface area region including a reflective surface area that is disposed generally opposite the first transmissive area, is at least one of semi-specularly reflective or diffusely reflective and has an on-axis average reflectivity of at least 90% (in some embodiments, at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 98.5%, or even at least 99%) for visible light of any polarization, and a remainder of the interior surface area has an on-axis average reflectivity of at least 98% (in some

embodiments, at least 98.5%, or even at least 99%) for visible light of any polarization;

a light guide disposed within the enclosure and between the first and second surface area regions, including substantially between the first transmissive area and the reflective surface area, with the light guide including a first opening for receiving light, wherein the first opening does not extend between the first transmissive area and the reflective surface area; and

a first light source positioned to introduce light into at least the first opening of the light guide. Typically, when light is emitted from a light source, the light is reflected multiple times by the interior surface. Optionally, the light assembly further comprises a partial reflector polarizer positioned closer to the first surface area region than to the second surface area region.

[006] It is understood that all the reflectivity values encompass all visible light reflected into a hemisphere (i.e., such values include semi-specular, specular, and diffuse reflections). The term "transmissive" as used herein means at least 50% (optionally, at least 60%, 65%, 70%, 75%, 80%, 85%, or even at least 90%) of the photons for at least one wavelength in the of light (e.g., in the visible spectrum) striking the area/film/element/etc. are transmitted through and exit the area/film/element/etc, as applicable.

[007] Light assemblies described herein can be useful as functional or decorative elements, for example, in displays, signs, and vehicles (e.g., automobile, trucks, etc.). Useful embodiments of light assemblies described herein for vehicles can include automobile and truck (vehicle) lighting, dash lighting, instrument cluster lighting, door sill lighting, dome lighting, and under cabinet lighting. Brief Description of the Drawings

[008] FIGS. 1-5 are a cross-sectional views of exemplary lighting assemblies described here.

[009] FIGS. 6-8 are schematic side views of backlights containing a hollow recycling enclosure, comparing the effects of specular, Lambertian, and semi-specular reflectors.

Detailed Description

[0010] Referring to FIG. 1, exemplary lighting assembly 110 has enclosure 111 having interior surface 112 and first transmissive area 113. Interior surface 112 comprises first surface area region 114 and second surface area region 115, which is generally opposite first surface area region 114. The first transmissive area 113 is within first surface area region 114. Interior surface 112 also comprises reflective surface area 116, which is generally opposite the first transmissive area 113, is within surface area region 115, is semi-specularly reflective and has an on-axis average reflectivity of at least 90%. First light source 117 is positioned at least partially in opening 118 of light guide 120 which is within enclosure 111.

[0011] Referring to FIG. 2, exemplary lighting assembly 210 has enclosure 211 having interior surface 212 and first transmissive area 213. Interior surface 212 comprises first surface area region 214 and second surface area region 215, which is generally opposite first surface area region 214. The first transmissive area 213 is within first surface area region 214. Interior surface 212 also comprises reflective surface area 216, which is generally opposite the first transmissive area 213, is within surface area region 215, is semi-specularly reflective and has an on-axis average reflectivity of at least 90%. First light source 217 is positioned at least partially in opening 118 of light guide 220 which is within enclosure 211.

[0012] Referring to FIG. 3, exemplary lighting assembly 310 has alphanumeric bezel 319 and enclosure 311 having interior surface 312 and first transmissive area 313. Interior surface 312 comprises first surface area region 314 and second surface area region 315, which is generally opposite first surface area region 314. The first transmissive area 313 is within first surface area region 314. Interior surface 312 also comprises reflective surface area 316, which is generally opposite the first transmissive area 313, is within surface area region 315, is semi-specularly reflective and has an on-axis average reflectivity of at least 90%. First light source 317 is positioned at least partially in opening 318 of light guide 320 which is within enclosure 311.

[0013] Referring to FIG. 4, exemplary lighting assembly 410 has alphanumeric bezel 419 and enclosure 411 having interior surface 412 and first transmissive area 413. Interior surface 412 comprises first surface area region 414 and second surface area region 415, which is generally opposite first surface area region 414. The first transmissive area 413 is within first surface area region 414. Interior surface 412 also comprises reflective surface area 416, which is generally opposite the first transmissive area 413, is within surface area region 415, is semi-specularly reflective and has an on-axis average reflectivity of at least 90%. First light source 417 is positioned at least partially in opening 418 of light guide 420 which is within enclosure 411.

[0014] Referring to FIG. 5, exemplary lighting assembly 510 has enclosure 511 having interior surface 512 and first transmissive area 513. Interior surface 512 comprises first surface area region 514 and second surface area region 515, which is generally opposite first surface area region 514. The first transmissive area 513 is within first surface area region 514. Interior surface 512 also comprises reflective surface area 516, which is generally opposite the first transmissive area 513, is within surface area region 515, is semi-specularly reflective and has an on-axis average reflectivity of at least 90%. First light source 517 is positioned at least partially in opening 518 of light guide 520 which is within enclosure 511.

[0015] The enclosure can be made of any of a variety of materials, including plastic, metal, wood, etc. The shape of the enclosure may be any of a variety of shapes including generally rectangular and triangular (including with squared off edges (internal and/or external), as well as those with oblong or rounded edges (internal and/or external)), as well as elliptical, and other Euclidean geometrical shapes.

[0016] Desirable length to width ratios of the enclosure are, for example, in a range from 1 :1 to 40:1 (in some embodiments, 10:1 to 40:1, 15:1 to 40:1, 20:1 to 40:1, 25:1 to 40:1, or even 30:1 to 40:1). Desirable length to height (i.e., first surface area region to generally opposed, second surface area region) ratios of the enclosure are, for example, in a range from 20:1 to 150:1 (in some embodiments, in a range from 50:1 to 100:1). [0017] Suitable light guides and light extraction devices are known in the art and are commercially available. Exemplary light guides are made of solid acrylic. Optionally, the light guide further comprises an additional opening(s) (e.g., a second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, or more). Optionally additional openings (or at least a portion thereof) are generally aligned. Openings can be made by convention techniques including drilling into the interior. The openings are shaped to allow light from the light source(s) to enter the interior of the light guide, and in some embodiments, also hold the light source in place. Typically, there is an air gap between the end of the light source and the light guide. The internal surface of the opening(s) in the light guide can be left in an unpolished state as this my further disperse the light, or it can be, for example, partially polished.

[0018] Exemplary light sources include at least one of an incandescent light, a light emitting diode, or an arc discharge lamp. Such light source(s) are well known and available in the art. Suitable light emitting diodes are known in the art, and are commercially available. Such light emitting diodes include those having Lambertian light emission pattern. In some embodiments, the LED may be used with a wedge-shaped reflector so that light may be emitted into the enclosure with a restricted or partially collimated angular distribution.

Further, in some embodiments, light sources that at least partially collimate the emitted light may be preferred. Such light sources can include lenses, extractors, shaped encapsulants, or combinations thereof of optical elements to provide a desired output into the enclosure.

Further, the light source can include injection optics that partially collimate or confine light initially injected into the enclosure to propagate in directions close to a transverse plane (the transverse plane being parallel to the output area of the light source) (e.g., an injection beam having an average deviation angle from the transverse plane in a range from 0° to 45°, or 0° to 30°, or even 0° to 15°).

[0022] LEDs are available in a variety of power usage ratings, including those ranging from less than 0.1 watt to 5 watts (e.g., power usage ratings up to 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 4, or even up to 5 watts) per LED. LEDs are available in colors ranging from violet (about 410 nm) to deep red (about 700 nm). Basic colors of LEDs are blue, green, red and amber, although other colors, such as white, are also available. Ultraviolet LEDs can also be used. These can be used, for example, with a down converting phosphor to convert their emitted light to visible light.

[0023] Light from a light source (e.g., a light emitting diode) can be introduced into an opening(s) in the light guide in a variety of ways. For example, a light source (e.g., an LED (chip)) itself can be placed inside (including partially inside) the opening(s). A lens connected to a light source (e.g., an LED) can protrude into (including partially inside) the opening(s) even though the light source itself is outside the enclosure. In some cases, a light source (e.g., LED) can be located a meter away or more and have its light transported to the enclosure by, for example, a light fiber system. Light fiber systems use total internal reflection to propagate light from the injection end of the fiber to an exit point. The exit end of the fiber can be inserted into the enclosure, and optionally used with collimation technique (e.g., lenses or an external collimating wedge). Techniques of transporting light in a solid medium include low absorption solids (e.g., low loss glass fiber or acrylic fiber). It is often preferable to use a lower refractive index cladding surrounding the glass or acrylic core. The low index cladding prevents or reduces accidental light leakage that may occur from scratching, or objects physically touching the core. Further, for example, it is possible to use a hollow technique for light transport rather than solid. In this case a cavity comprised of a low-loss omnidirectional specular, or semi-specular mirror can be used. Light, preferably collimated, is injected into one end of this transport cavity, and by multiple reflections is transported to an extraction point which may be, in the case of a tube, the opposite end. The extraction end of this transport system can be positioned proximate the enclosure so as to introduce light into the opening(s).

[0023] Optionally, the lighting assembly further comprises at least one additional (e.g., a second, third, fourth, fifth, or more) light source(s). For example, a light source

corresponding to any additional openings in the light guide.

[0019] A "specular" reflector, sometimes referred to as a mirror, performs according to the optical rule that "the angle of incidence equals the angle of reflection." This is seen in the hollow enclosure 816 of FIG. 6. There, the front and back reflectors, 812, 814 are both specular. A small portion of an initially launched oblique light ray 850 is transmitted through the front reflector 812, but the remainder is reflected at an equal angle to the back reflector 814, and reflected again at an equal angle to the front reflector 812, and so on as illustrated. This arrangement provides maximum lateral transport of the light across the enclosure 816, since the recycled ray is unimpeded in its lateral transit of the enclosure 816. However, no angular mixing occurs in the enclosure, since there is no mechanism to convert light propagating at a given incidence angle to other incidence angles.

[0020] A "Lambertian" reflector, on the other hand, redirects light rays equally in all directions. This is seen in the hollow enclosure 916 of FIG. 7, where the front and back reflectors 912, 914 are both Lambertian. The same initially launched oblique light ray 950 is immediately scattered in all directions by the front reflector 912, most of the scattered light being reflected back into the enclosure 916 but some being transmitted through the front reflector 912. Some of the reflected light travels "forward" (generally to the right as seen in FIG. 7), but an equal amount travels "backward" (generally to the left). By forward scattering, we refer to the lateral or in-plane (in a plane parallel to the scattering surface in question) propagation components of the reflected light. When repeated, this process greatly diminishes the forward directed component of a light ray after several reflections. The beam is rapidly dispersed, producing minimal lateral transport.

[0021] A "semi-specular" reflector provides a balance of specular and diffusive properties. In the hollow enclosure 1016 of FIG. 8, the front reflector 1012 is purely specular but the back reflector 1014 is semi-specular. The reflected portion of the same initially launched oblique light ray 1050 strikes the back reflector 1018, and is substantially forward-scattered in a controlled amount. The reflected cone of light is then partially transmitted but mostly reflected (specularly) back to the back reflector 1014, all while still propagating to a great extent in the "forward" direction.

[0022] A "diffuse" reflector is a material that, relative to the position of the source, has a proportion of forward and backward reflected flux that is substantially equal (i.e., up and including 60%/40% forward/backward, wherein greater than 60% forward is semi-specular.

[0023] Specularly reflective surfaces having an on-axis average reflectivity of at least 98% for visible light by the light source(s) of any polarization can be provided, for example, by a fϊlm(s) such as those described in U.S. Pat. Nos. 5,882,774 (Jonza et al.) and 6,641,880 (Deyak et al.), the disclosures of which are incorporate herein by reference; additional details regarding such films can also be found in said patents. Embodiments of such films are marketed by 3M Company, St. Paul, MN, under the trade designation "VIKUITI ENHANCED SPECULAR REFLECTOR FILM." Other suitable reflective materials include those marketed by Alanod Aluminum- Veredlung GmbH & Co., Ennepetal, Germany, under the trade designation "MIRO-2 ANODIZED ALUMINUM FILM").

[0024] Semi-specular reflective surfaces can be provided, for example, by (1) a partial transmitting specular reflector plus a high reflectance diffuse reflector; (2) a partial

Lambertian diffuser covering a high reflectance specular reflector; (3) a forward scattering diffuser plus a high reflectance specular reflector; or (4) a corrugated high reflectance specular reflector. Additional details regarding semi-specular reflective materials, can be found, for example, in PCT Application No. US2008/864115 (Attorney Docket No.

63032WO003), the disclosure of which is incorporated herein by reference.

[0025] Optionally, light assemblies described herein further comprising additional transmissive areas (e.g., one two, three, four, five, six, seven, eight, nine, ten, or more additional transmissive areas) within the second surface area region. Optionally, the transmissive area(s) are in the shape of, or otherwise include, at least one alphanumeric indicia, at least one trademark indicia, or both alphanumeric and trademark indicia. The transmissive area can be made of any material suitable for the particular light assembly desired, which may include acrylic, polycarbonate, plastics, and glass, as well as a material described below for the transmissive element.

[0026] Films for constructing lighting assemblies described herein may be supported, for example, by a transmissive substrate. Suitable transmissive substrates can include optical films, sheets, or plates. Suitable materials include glass, transmissive engineering thermoplastics (e.g., polycarbonate, polystyrene, acrylic, styrene acrylonitrile, cyclo olefin polymer ("COP"; available from Zcoπ Chemicals L.P., Louisville, KY), polyethylene terephthalate, polyethylene 2,6-naphthalate, and fluoropolymers).

[0027] Optionally, lighting assembly described herein further comprising a comprising a tinted transmissive element(s) (e.g., a film(s)) disposed between the light guide and the first surface area region, the light guide and the transmissive area(s) (e.g., adhered to the transmissive area(s)) and/or the other side of the transmissive area(s)). Suitable films are known in the art and include tinted (e.g., dyed or pigmented) films and color shifting films. Transmissive tinted and color shifting films are available, for example, from 3M Company under the trade designation "SCOTCHCAL 3630" in about 60 different colors. [0028] "Color shifting film" as used herein refers to a film comprising alternating layers of at least a first and second layer type, wherein the first layer type comprises a strain hardening polymer (e.g., a polyester), wherein the film has at least one transmission band and one reflection band in the visible region of the spectrum, the transmission band having an average transmission of at least 70%, and wherein at least one of said transmission band and reflection band varies at normal incidence by less than about 25 nm over a square inch.

Optionally, the film comprises alternating polymeric layers of at least a first and a second layer type, wherein the film has at least one transmission band and at least one reflection band in the visible region of the spectrum, and wherein at least one of the transmission band and reflection band has a band edge that varies at normal incidence by no more than 8 nm over a distance of at least 5.1 cm (2 inches) along each of two orthogonal axes in the plane of the film. Optionally, at least one of the transmission band and the reflection band has a bandwidth at normal incidence that varies by no more than 2 nm over a surface area of at least 10 cm². Optionally, the film has exactly one transmission band in the visible region of the spectrum. Optionally, the film has exactly one reflection band in the visible region of the spectrum. Color shifting films can be made, for example, as described in U.S. Pat. No.

6,531,230 (Weber et al.), the disclosure of which is incorporate herein by reference;

additional details regarding such films can also be found in said patent.

[0029] Films typically have a major surface covered with adhesive. Suitable adhesives are well known in the art (e.g., pressure sensitive adhesives) will generally be found on one surface of the film (continuous or portions depending on the embodiment involved) and allows the film to be attached to another surface.

[0030] Suitable light assembly configurations can be designed and assembled using known techniques by one skilled in the art after reviewing the instant disclosure.

[0031] Light assemblies described herein are useful as functional or decorative elements, for example, in displays, signs, and vehicles (e.g., automobile, trucks, etc.). Useful embodiments of light assemblies described herein for vehicles include automobile and truck (vehicle) lighting, dash lighting, instrument cluster lighting, door sill lighting, dome lighting, and under cabinet lighting.

[0032] Advantages and embodiments of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All parts and percentages are by weight unless otherwise indicated.

Example

[0033] A light assembly as shown in FIG. 1 was constructed. Nine holes were drilled into the 14 cm long side a 14 cm by 4.5 cm by 0.6 cm piece of polycarbonate (obtained under the trade designation "LEXAN" from SABIC Innovative Plastics (formerly General Electric Plastics), Riyadh, Saudi Arabia). The holes were about 3 mm in diameter, and about 6 mm deep into the polycarbonate. The holes were left in an as-drilled, unpolished state.

[0034] The holes where sized to allow a light emitting diode (obtained under the trade designation "KINGBRIGHT LED X-BRITE" (part no. WP7104RWC/J) obtained from Mouser Electronics, Mansfield, TX) to fit snugly into each hole. After putting the light emitting diodes in their respective holes, there was a gap of about 2 mm between the end of deepest part of the hole and the end of the light emitting diode.

[0035] The two major surfaces of the polycarbonate ("LEXAN") was cleaned using a common window cleaner and paper towels. Referring to FIG. 1, transmissive area 113 was defined by measuring and marking with a scribe on the cleaned major surface. A region (116) sized to match transmissive area 113 was marked out on the other major surface. All external surfaces of the polycarbonate ("LEXAN") but transmissive area 113 and the region (116) sized to match transmissive area 113 were covered with a specularly reflective film having an on-axis average reflectivity of at least 98% for visible light (available under the trade designation "VIKUITI ENHANCED SPECULAR REFLECTOR FILM" from 3M Company, St. Paul, MN). The film was adhered to the polycarbonate ("LEXAN") via an adhesive on the film.

[0036] Next a diffusely reflective film (available under the trade designation "LIGHT ENHANCEMENT FILM 3635-100" from 3M Company) was applied via an adhesive on the film to the region (116) sized to match transmissive area 113. The portion of the specularly reflective film covering the drilled openings was removed, and the light emitting diodes inserted therein. After wiring the light emitting diodes for a voltage of 3.2 volts, power was supplied to the light emitting diodes, and a uniform light was observed to be emitting from transmissive area 113.

[0037] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.

Claims

What is claimed is:

1. A lighting assembly comprising:

an enclosure having an interior surface and a first transmissive area, the interior surface comprising a first surface area region and a second surface area region disposed generally opposite the first surface area region, the first transmissive area being within the first surface area region, the second surface area region including a reflective surface area that is disposed generally opposite the first transmissive area, is at least one of semi-specularly reflective or diffusely reflective and has an on-axis average reflectivity of at least 90% for visible light of any polarization, and a remainder of the interior surface area has an on-axis average reflectivity of at least 98% for visible light of any polarization;

a first light source positioned to introduce light into at least the first opening of the light guide.

2. The lighting device of claim 1, wherein light emitted from the first light source is reflected multiple times by the interior surface.

3. The lighting device of any preceding claim, wherein the first light source is at least partially within the first opening of the light guide.

4. The lighting device of any preceding claim, wherein the light guide further comprises a second opening, and the lighting device further comprises a second light source positioned to introduce light into at least the second opening of the light guide.

5. The lighting device of claim 4, wherein the second light source is at least partially within the second opening of the light guide.

6. The lighting device of any preceding claim, further comprising a partial reflector polarizer positioned closer to the first surface area region than to the second surface area region.

7. The lighting assembly of any preceding claim, wherein the first surface area region is semi-specularly reflective or specularly reflective.

8. The lighting assembly of any preceding claim, wherein the on-axis average reflectivity for the first surface area region is provided by at least one film.

9. The lighting assembly of any preceding claim, wherein the on-axis average reflectivity for the remainder of the interior surface area is provided by at least one film.

10. The light assembly of any preceding claim, wherein the enclosure is generally rectangular in shape.

11. The light assembly of any preceding claim, wherein the first transmissive area is in the shape of at least one indicia.

12. The light assembly of any preceding claim, further comprising additional transmissive areas within the first surface area region.

13. The light assembly of claim 12, wherein each of the transmissive areas is in the shape of at least one indicia.

14. The lighting assembly of any preceding claim, further comprising a film that is at least transmissive and disposed between the light guide and the transmissive area.

15. The lighting assembly of any preceding claim that is a door sill lighting assembly.

16. A vehicle comprising the lighting assembly of any preceding claim.