CN112524500B

CN112524500B - Asymmetric light intensity distribution from a lighting device

Info

Publication number: CN112524500B
Application number: CN202011230581.XA
Authority: CN
Inventors: F.S.狄亚娜; G.古思; J.登布里延; I.布拉克
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2016-02-22
Filing date: 2017-02-21
Publication date: 2023-07-28
Anticipated expiration: 2037-02-21
Also published as: JP2019507477A; CN109416154B; JP2022025150A; CN112524500A; CN109416154A; JP7042962B2

Abstract

In one embodiment, an overhead street lamp (luminaire) is formed with an asymmetric light intensity distribution, wherein the peak intensity is greatest along the direction of the street, lower straight across the street, and much lower on the residential side of the street. Around the edge of the circular transparent light guide are white LEDs that inject light into the light guide. To help control the asymmetry of the light intensity distribution, saw-tooth shaped grooves are formed in the light guide surface opposite the light emitting surface and parallel to the street. Gaussian diffusers are used to partially diffuse light. By a suitable choice of the grooves, the gaussian diffuser and the relative amounts of light emitted by the LED segments around the light guide, the desired asymmetric light intensity distribution is achieved while the direct view of the light exit surface appears as uniform light.

Description

Asymmetric light intensity distribution from a lighting device

RELATED APPLICATIONS

The present application is a divisional application of chinese patent application with application number 201780025174.5 entitled "asymmetric light intensity distribution from a lighting device" filed on day 21, 2, 2017.

Cross Reference to Related Applications

The present application claims priority from U.S. provisional patent application Ser. No. 62/298,355 filed on 22 nd a year 2016, U.S. provisional patent application Ser. No. 62/328,402 filed on 27 th a year 4, and European patent application Ser. No. 16173295.3 filed on 7 th a year 2016. U.S. provisional patent application Ser. No. 62/298,355, U.S. provisional patent application Ser. No. 62/328,402, and European patent application Ser. No. 16173295.3 are incorporated herein by reference.

Technical Field

The present invention relates to general illumination using Light Emitting Diode (LED) lamps, and in particular, to an illumination device that produces an asymmetric light intensity distribution suitable for illuminating streets, roads, walls, or other areas.

Background

Conventional street lamps are being replaced with more efficient and reliable LED lighting. The desired light intensity distribution provides the highest peak light intensity along the street, while a very small light intensity is in the opposite direction from the street. The side of the lighting device facing away from the street is herein referred to as the "residential side", and the side of the lighting device facing towards the street is herein referred to as the "street side". The light intensity in the house-side direction should only be sufficient to illuminate the sidewalk or curb along the street.

Modern street lamps using LEDs control the light intensity distribution by using an asymmetric lens over the high power LEDs. Alternatively, conventional secondary optics are used to direct light downward and sideways while blocking light emission in the home-side direction. Such street lamps have a high glare when the observer looks directly at the lighting device. For example, one type of street lamp uses two parallel columns of eight high power white LEDs, with a separate lens over each LED. When viewed directly, 16 very bright point sources can be seen. This is known as pixelated illumination and is aesthetically undesirable.

There is a need for an efficient lighting device using LEDs with a controllable asymmetric light intensity distribution, such as optimized for overhead street lighting, wherein the lighting device has a non-pixelated pattern when in direct view.

Disclosure of Invention

In one embodiment, an overhead street lamp (luminaire) is formed with an asymmetric light intensity distribution, wherein the peak intensity is highest along the direction of the street, lower straight across the street, and much lower on the residential side of the street. The intensity distribution may be a mirror image perpendicular to the street.

The illumination apparatus includes a circular transparent light guide, such as about 15 inches (38 cm) in diameter and about 0.5 cm thick. The circular metal frame supports the light guide. Around the edge of the light guide are white light LEDs on flexible strips that inject light into the polished edge of the light guide to maintain directionality.

The LEDs on the strip are divided into a plurality of sections, such as twelve sections (depending on the size of the lighting device). The segments may be designed or controlled to emit different amounts of light to help create the desired asymmetric light intensity distribution. The amount of light emitted by each segment may be controlled by varying the number of LEDs in each segment or varying the current to each segment. In another embodiment, the light emission from each section is the same. Each section may contain LEDs connected in series, and the sections may be connected in parallel.

In another embodiment, the LEDs are placed at a variable pitch or density, and potentially have one or more rows of LEDs depending on the desired concentration to achieve the desired azimuthal light intensity distribution (i.e., in the horizontal angular plane).

Light injected into the light guide is internally reflected until the light is extracted, such that the light is slightly mixed within the light guide while still having some directionality.

In order to also control the asymmetry of the light intensity distribution, parallel saw-tooth shaped grooves are formed in the surface of the light guide opposite to the light emission surface. These grooves are parallel to the street.

In one embodiment, all of these grooves are identical and their angles and spacing can be designed to fine tune the light distribution and luminance uniformity across the emitting surface. The angled surfaces of the grooves generally face the home side LEDs and the vertical surfaces of the grooves generally face the street side LEDs such that light from both the home side LEDs and the street side LEDs is generally directed toward the street after reflecting off the groove surfaces. The spacing between these grooves may vary along the light guide in order to spread the light more uniformly across the light exit surface of the light guide.

In another embodiment, the angles and depths of the zigzag grooves are gradually increased toward the street side in order to reduce the amount of light reflected back toward the home side and further improve luminance uniformity across the emitting surface.

On the light emitting side of the lightguide may be printed translucent dots, such as epoxy-based dots, which may help to increase light extraction efficiency and widen the street-side beam. These points may be about 1 mm in diameter and have a gaussian light emission (as opposed to lambertian). The gaussian spot slightly diffuses the incident light in the direction of the incident light, such as providing a half-maximum half-width spread of 12 degrees. The dots may be uniformly arranged on the surface of the light guide and occupy about half the area of the light emitting surface. Alternatively, the dots may have a variable size distribution or a variable density distribution to improve luminance uniformity across the emission surface.

Instead of dots, a gaussian continuous diffusion layer or surface texture (such as a finish of about "frosted glass") may also be used.

These diffusing elements may also be placed on the back surface of the light guide and alternate with grooves. The light from the diffusing element will be further mixed within the light guide to improve uniformity.

A reflector is positioned over the light guide to reflect back any upward light escaping from the light guide.

Additional transparent optical plates inserted below the exit surface of the light guide may be used to protect the light guide and provide some additional light distribution control, such as filtering out high angle light rays to reduce glare. Texture may further be added to the light guide surface to reduce or inhibit light directed toward the residential side.

By appropriate selection of the grooves, the relative amounts of street side lighting and residential side lighting can be controlled. By controlling the amount of light emitted by each LED segment, the asymmetric light intensity distribution can be further controlled. By using gaussian points (or other suitable diffusers), the light exiting the light guide remains directional but sufficiently diffuse such that an observer looking directly at the light emitting surface of the light guide sees generally uniform, comfortable light.

In other embodiments, the light guide may be rectangular, rectangular with rounded corners, parallelepiped (with possibly rounded corners), or elliptical. These light guides may also be formed in a wedge shape, eliminating the need for zigzag grooves. Gaussian points or other diffusers may be employed.

In another rectangular luminaire, the luminaire is angled relative to the street, and the LED strips are positioned along only two house side edges, to cause a large portion of the light to be directed along the street. Prisms molded into the rear surface of the light guide further control the asymmetry of the light intensity distribution. Gaussian dots (Gaussian dots) or other diffusers may be employed.

Instead of injecting the LED light edge into the side of the light guide, the LEDs may be positioned within holes formed near the outer edge of the light guide.

The lighting device may be used for any other purpose where an asymmetric light intensity distribution is desired.

Other embodiments are disclosed.

Drawings

Fig. 1 is a perspective view of an embodiment of the present invention (lighting device) used as an overhead street lamp.

Fig. 2 is a light intensity distribution in a horizontal light cone intersecting a vertical angle for which the emitted luminous intensity (candela) is greatest from the test conducted on the lamp of fig. 1, showing the highest intensity oriented along the street, the lower light intensity oriented across the street, and the lowest light intensity oriented toward the residential side (as opposed to the street side).

Fig. 3 is a light intensity distribution in a vertical plane intersecting a horizontal angle for which emitted luminous intensity (candela) is greatest from the test performed on the lamp of fig. 1, showing the highest light intensity oriented at a slightly downward angle along the street, and a much lower light intensity oriented toward the residential side.

Fig. 4 is a top-down view of the luminaire with the top cover removed, showing LED sections surrounding a circular light guide with reflector sheets over the top.

Fig. 5 is a bottom-up view of the light guide showing gaussian dots (about 1 mm diameter) printed on the light emitting surface. In one embodiment, these points occupy about half of the bottom surface of the light guide.

Fig. 6A is a front view of a section of serially connected LEDs on a flexible printed circuit strip or rigid printed circuit board, where the section contains 5 LEDs.

Fig. 6B is a front view of another section of serially connected LEDs on a flexible printed circuit strip or rigid printed circuit board, where the section contains only 2 LEDs to reduce light output.

Fig. 7 shows an array of parallel saw-tooth shaped grooves formed on the rear surface of the light guide opposite the surface containing the dots.

Fig. 8 is a cross-sectional view of a portion of the illumination device of fig. 7, showing LEDs emitting light into the edge of the light guide, gaussian points (directional but diffuse) on the light emitting surface, parallel saw-tooth shaped grooves in the rear surface, and reflectors over the light guide.

Fig. 9 shows the lighting device of fig. 8, but wherein the grooves are identical and their spacing is varied.

Fig. 10 shows the lighting device of fig. 8, but wherein the grooves are identical and diffusion points are printed between the grooves.

Fig. 11 is a cross-sectional view of a portion of a rectangular lighting device, wherein wedge shapes may be used instead of the grooves of fig. 8-10, and wherein gaussian points are also used.

Fig. 12 is a top-down view of the lighting device of fig. 11, showing how LEDs may only need to be positioned along opposite edges of a wedge-shaped light guide.

Fig. 13 is a top-down view of a flat rectangular luminaire in which the light guide is positioned at an angle to the street, an array of prisms of varying depth are formed (e.g., molded) in the back surface to control asymmetric light intensity distribution (lower intensity toward the residential side), and LED strips are positioned only on the residential side of the light guide to inject light primarily in the direction of the street.

Fig. 14 shows a single prism molded into the rear surface of the light guide of fig. 13, showing how light from two LED segments is internally reflected toward the street and away from the residential side. Other shapes of reflectors may be used.

Fig. 15 shows how LED segments in a circular lighting device (such as that shown in fig. 1) can output different light powers by controlling the current to the segments to achieve a desired asymmetric light intensity distribution.

Fig. 16 is a bottom-up view of a circular light guide having holes (such as 168 holes for a 15 inch lighting device) around its outer edge for receiving a ring of LEDs.

FIG. 17 is a cross-sectional view of the light guide of FIG. 16 further illustrating the LEDs within the holes and the reflector rings over the LEDs. The light guide comprises gaussian points and grooves or prisms as previously described.

The same or similar elements are labeled with the same numerals.

Detailed Description

Although the present invention may be used in a wide variety of applications, examples are shown that are optimized for use as street lights. Fig. 1 shows a lighting device 10 supported by a support structure 12 above a street 14. The asymmetric light intensity distribution of the lighting device 10 is described with respect to the street side and the home side. The desired light intensity distribution is a high light intensity along a length of the street, a lower light intensity extending across the street, and a much lower light intensity emitted in the opposite direction towards the residential side. The light along the length of the street merges with light from adjacent street lamps to provide a fairly uniform illumination of the entire street.

The examples described below do not present a high brightness pixelated light pattern when viewed directly by an observer. Instead, the light spreads over the entire bottom surface of the light emitting portion of the illumination device to produce a substantially uniform diffuse light that is much more comfortable than the pixelated light pattern.

Fig. 2 shows the desired light intensity distribution 16 (measured in candelas) in a horizontal light cone intersecting the emitted luminous intensity (candela) for its maximum vertical angle, obtained from the test conducted on the lamp of fig. 1, with the lighting device 10 located at the intersection of the axes. Many other similar distributions are achievable, and the optimal distribution may depend on the particular characteristics of the street to be illuminated. For example, for narrower streets, the street-side intensity distribution oriented perpendicular to the street may be concave. In the example shown, the peak light intensity oriented along (generally parallel to) the street is 2-3 times higher than the peak light intensity oriented directly perpendicular to the street, and the peak light intensity oriented towards the residential side is less than one third of the light intensity oriented directly perpendicular to the street. Such house-side lights may be used to illuminate a small road along a street, or for a curb area if the lighting device is fully suspended into the street.

Fig. 3 shows the desired light intensity distribution 18 (measured in candelas) in a vertical plane intersecting a horizontal angle for which the emitted luminous intensity (candela) is greatest, obtained from the test performed on the lamp of fig. 1, with the lighting device 10 located at the intersection of the axes. In the example shown, the highest peak light intensity is oriented at a slightly downward angle along the street, and the much lower peak light intensity is oriented toward the residential side. The street side peak intensity is far more than three times the peak intensity oriented toward the house side.

The intensity of light is substantially mirrored with respect to a centerline perpendicular to the street.

Many other asymmetric light intensity distributions can be achieved using the structures described below.

Fig. 4 is a top-down view of a portion of the lighting device 10 of fig. 1 with the top cover removed. A circular metal frame 20 with a bottom opening mounts a flexible circuit tape around its inner periphery containing a linear array of white light LEDs. White LEDs may be high power, gaN-based blue emitting LEDs with YAG phosphor (to generate yellow light) to generate white light. Other phosphors may be added to achieve a desired color temperature or Color Rendering Index (CRI).

In one embodiment, the frame 20 is about 15 inches in diameter and there are about 168 LEDs. The LEDs are divided into a plurality of sections 22, such as 12 sections, wherein the LEDs in a single section 22 are connected in series and the plurality of sections 22 are connected in parallel. If the LED has a forward voltage of 3.5 volts, the operating voltage of the lighting device 10 is about 42 volts.

The circular light guide 24 of fig. 5 is located in the frame 10 with the printed dots 26 facing down towards the street. The light guide 24 may be a transparent polymer, such as PMMA, that is about 4-5 a mm a thick. The printed dots 26 will be described more fully later with respect to fig. 8.

A reflector sheet 28 (fig. 4) is positioned over the light guide 24 and LEDs to reflect all light downward (the reflector sheet 28 is shown as smaller so as not to obscure the LEDs). In one embodiment, the reflector sheet 28 is a specular or slightly diffuse lens to substantially maintain the directionality of the light rays, thereby achieving better control of the asymmetry of the light intensity distribution. In another embodiment, the reflector sheet 28 may have a white surface to greatly enhance diffusion of light. The reflector sheet 28 may be spaced apart from the light guide 24 or directly on the light guide surface.

A metal cover (not shown) is attached over the lighting device 10.

In one embodiment, to provide more control over the asymmetry of the light intensity distribution, the LED segments 22 are designed to emit different amounts of light. Fig. 6A shows an LED segment 30 designed to emit high brightness, the LED segment 30 being for positioning along a rear portion (home side) of the lighting device 10, such as in the position shown in fig. 4, such that the high brightness is oriented along a street and away from the home side. Five LEDs 32 are shown connected in series by conductors 34 on a flex circuit 36. In a practical embodiment, there may be about 14 LEDs in one section 22. The LED 32 has a generally lambertian emission.

Fig. 6B shows another LED segment 38 that also may be used in the lighting device 10 to output reduced brightness. In this example, there are only 2 LEDs 32 in the section 38. The section 38 may be positioned at the location shown in fig. 4 to provide low brightness in the direction of the residential side.

The LED segments 22 in other locations around the light guide 24 may be designed with different light outputs to further tailor the light intensity distribution. Alternatively, different currents may be applied to the exact same LED segment 22 to tailor the light output from the segment 22.

In one embodiment, each section 22 around the light guide is identical and receives the same current, and the light intensity distribution of the lamp is customized using other techniques (such as those described below).

Fig. 7 shows the light guide 24 of fig. 5, showing parallel grooves 40 molded or machined into the surface of the light guide 24 opposite the surface having the dots 26. The grooves 40 are zigzag. The width of each trench 40 may be between 0.5-4 mm. The grooves 40 redirect the incoming light downward toward the street side and reduce the amount of light reflected back internally from the edge of the light guide 24.

Fig. 8 is a cross-sectional view of the lighting device 10, showing one embodiment of the grooves 40 and the printed dots 26. The LEDs 32 mounted on the flex circuit 36 are shown as emitting white light into the light guide 24. Light is generally reflected off the smooth inner surface of the light guide 24 by TIR until the light is reflected down the angled grooves 24 or impinges on the translucent dots 26. The dots 26 may be epoxy-based and contain diffusing particles (e.g., tiO2, high refractive index microbeads (micro-beads), etc.) that diffuse only slightly the direction of light diffracted into the light rays 42, such as by expanding the light by a HWHM of about 12 degrees. This maintains some directionality of the incoming light, but sufficiently diffuses the light so that the illumination device appears uniformly white to the viewer. Some of the diffuse light from the dots 26 is also reflected back into the light guide 24 to eventually escape.

The trench 40 has a length parallel to the street, with the inclined surface of the trench 40 angled downward to receive a majority of the incident light from the residential side LED (on the left side). It should be noted how the grooves 40 become deeper and deeper into the light guide 24 at larger and larger angles to progressively increase the chance that light from the residential side of the lighting device will be reflected downwards by the grooves 40. This greatly reduces the amount of light that will reflect back toward the home side off the right side edge of the light guide 24, thereby reducing the amount of light emitted toward the home side. Furthermore, as the amount of light from the home side LEDs within the light guide 24 is progressively reduced by being emitted along the length of the light guide 24 while being increasingly intercepted by the varying depth/angle grooves 40, the varying depth/angle of the grooves 40 results in more uniform orientation of the light from the home side LEDs towards the light exit surface of the light guide 24. Thus, there is good light uniformity at the light exit surface of the light guide 24 while still maintaining the asymmetric light intensity distribution shown in fig. 2 and 3.

Conversely, the generally vertical surface of the angled trench 40 results in a large amount of the street side LED light being reflected back toward the street side, enhancing the light emission from the street side. Since the street side LEDs are positioned 180 degrees around the forward direction of the light guide 24, light from the street side LEDs will reflect off the home side and be emitted toward the street. In another embodiment, the grooves 40 all have the same angle and become deeper and deeper, and the width of the grooves 40 progressively increases toward the street side.

Any light escaping from the top of the light guide 24 is reflected back into the light guide 24 by the reflector sheet 28. As previously mentioned, the reflective sheet 28 may be specular (for maximum directionality), diffuse specular, or white (for minimum directionality).

In one embodiment, since the dots 26 cover about half of the bottom surface of the light guide 24, about 50 percent of the light entering the light guide 24 exits without being diffused by the dots 26, and the remaining 50 percent is diffused by the dots 26. The points 26 may be other than hemispherical, such as rounded rectangles, rounded triangles, flat-topped circles, flat-sided prisms, or other suitable shapes that produce diffuse gaussian emissions.

By controlling the depth of the grooves 40 and the angle thereof, the light intensity distribution of fig. 2 and 3 can be obtained. Additional control of the distribution may be obtained by controlling the relative light output power of the different LED segments 22 (fig. 4).

Fig. 9 shows the lighting device of fig. 8, but wherein the grooves 43 in the light guide 44 are identical and their spacing is varied. The grooves 43 become closer together as the grooves 43 approach the street side to reflect more light downward. As the light from the residential side LEDs progressively decreases along the light guide 44, the increased density of the grooves 43 results in more uniform light along the light exit surface of the light guide 44 in direct view.

In another embodiment, the grooves 43 are uniformly spaced while still achieving the asymmetric light intensity distribution of fig. 2 and 3, as light from the residential side LEDs is generally directed downward by the angled surfaces of the grooves 43, and light from the street side LEDs is generally reflected back (and eventually downward) by the vertical surfaces of the grooves 43 facing the street side LEDs.

Fig. 10 shows the lighting device of fig. 8, but wherein the grooves 45 in the light guide 46 are identical and diffuse gaussian points 26 are printed between the grooves 45. The dots 26 redirect the incident light upward and downward in a diffuse/directional manner. The upwardly redirected light is reflected back downwardly by the reflector sheet 28. The light exit surface of the light guide 46 may have a diffusing layer 47, such as a laminate or formed by machining or molding the light guide 46. The amount of diffusion should be limited in order to achieve the asymmetric light intensity distribution of fig. 2 and 3.

Other diffusing elements may be formed on the grooved surface, such as roughening the surface or molding prisms into the surface.

Although circular lighting devices have some advantages over rectangular lighting devices, good asymmetric light intensity distribution can be achieved using rectangular lighting devices. Fig. 11 is a cross-section of a rectangular light guide 50 having an angled top surface (wedge shape) covered with a reflective sheet 52. Fig. 12 is a top-down view of the lighting device of fig. 11. The angled top surface causes a majority of the light emitted by the residential side LED (left side) to exit the light guide 50 away from the residential side. The light may exit the light guide 50 directly or be slightly diffused by the dots 26. Most of the light emitted by the street-side LEDs reflects off the opposite flat wall of the light guide 50 and is redirected out by the angled top surface and the dots 26.

Fig. 13 is a top-down view of a flat (non-wedge-shaped) light guide 56, the light guide 56 being angled relative to the street such that its front side is at a 45 degree angle relative to the street. LED strips 58 and 60 are positioned along adjacent sides of the light guide 56 on the residential side. Light from the LEDs is directed in the direction of the street. To redirect light down and sideways into the street, an array of prisms 62, shown in fig. 14, is molded into the rear surface of the light guide 56 to redirect light rays 63 toward the street. The location of the LED strips 58/60 mainly controls the directionality towards the street and away from the residential side. Some of the light reflects back off the opposite edge of the light guide 56 and produces small residential side-emission. The angle of the prism walls may be controlled to produce the asymmetric light intensity distribution of fig. 2 and 3 or other desired distribution. Gaussian spots may be printed on the light emitting surface of the lightguide 56.

Fig. 15 shows the general lighting device of fig. 4, but wherein the LED segments 64 have a brightness that is controlled by selecting different currents for the multiple segments 64 using a current control circuit 66. The circuit 66 may be a passive circuit (e.g., a resistor or metal interconnect pattern) or device that can be electronically controlled to achieve a desired light intensity distribution of the lighting device.

Instead of mounting LEDs around the edges of the light guide (separated by an air gap or more directly optically coupled), the LEDs on the flexible circuit may be positioned in holes formed around the outer edges of the light guide, such as shown in fig. 16 and 17. Fig. 16 shows through holes 70 formed around the periphery of light guide 72. In one embodiment, similar to those shown in fig. 4, LEDs 74 (fig. 17) may be arranged in multiple sections. The flexible circuit 76 supporting the LEDs 74 forms a loop. Reflective ring 78 is positioned over the top of aperture 70 and may also cover light guide 72. Light guide 72 may include grooves (fig. 8-10) and gaussian points 26 as previously described to create the asymmetric light intensity distribution of fig. 2 and 3.

The LED 74 in the aperture 70 of fig. 17 may be side-emitting, with a reflective layer formed directly on the top surface of the LED die over the phosphor layer.

Elliptical lighting devices are also contemplated.

It is contemplated that the techniques described herein are used to create designs with many other lighting devices in which a distribution of light is emitted much more around one arc than around another. For example, if the lighting devices are used to illuminate a narrow aisle and are positioned only about one foot from the ground, they may be relatively small (e.g., 4 inches in diameter) and they may have a light intensity distribution with very large and narrow (wide and narrow) side lobes, much shorter front lobes for the narrow aisle, and substantially no residential side emissions. Similar lighting devices may be used to illuminate a room to more uniformly protrude through the walls, wherein the light spreads more uniformly along the walls.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.

Claims

1. A lighting system, comprising:

a light guide configured to receive light from a plurality of light emitting diodes located near an outer edge of the light guide,

the outer rim comprises a first outer rim position,

the received light can be guided inside the light guide as guided light,

the light guide having a light emitting surface configured to allow at least a portion of the guided light to exit the light guide through the light emitting surface,

the light guide has a reflective surface opposite the light emitting surface,

the reflective surface is configured to reflect at least a portion of the guided light, such that the reflected portion remains in the light guide as guided light,

the reflective surface includes a plurality of grooves extending parallel to each other along the reflective surface,

each of the grooves extends into the reflective surface,

each groove comprising a first surface inclined at a respective angled surface inclination angle towards the first outer edge position, each groove comprising a second surface adjoining the first surface, the second surface being oriented orthogonal to the light emitting surface,

the depth of the groove increases with increasing distance from the first outer edge location,

the change in the angle of inclination of the angled surfaces is such that the acute angle between the first and second surfaces decreases with increasing distance from the first outer edge location,

the first and second surfaces are configured to reflect light in a direction away from the first outer edge location such that a majority of light exiting the light emitting surface travels in a direction away from the first outer edge location.

2. The lighting system of claim 1, wherein:

the light emitting surface includes a plurality of Gaussian diffusion dots printed thereon, an

Each gaussian diffusion dot comprises a plurality of microbeads disposed in an epoxy-based material, the microbeads having a refractive index that is different from the refractive index of the epoxy-based material.

3. The illumination system of claim 1, further comprising a reflector positioned adjacent to and parallel to the reflective surface, the reflector configured to reflect guided light exiting the light guide through the reflective surface back to the reflective surface.

4. The lighting system of claim 1, further comprising: a plurality of light emitting diodes located near an outer edge of the light guide and configured to guide light into the light guide to form the guided light.

5. The lighting system of claim 4, wherein:

the plurality of light emitting diodes are divided into discrete sections around the outer edge of the light guide, and

the first discrete section and the second discrete section comprise different numbers of light emitting diodes.

6. The lighting system of claim 4, wherein:

the plurality of light emitting diodes are divided into discrete sections around the outer edge of the light guide,

the light emitting diodes in each discrete section are electrically connected in series, and

the discrete sections are electrically connected in parallel.

7. The lighting system of claim 4, wherein:

the method further includes providing a first current to the first discrete section and providing a second current different from the first current to the second discrete section.

8. The lighting system of claim 7, wherein:

the first discrete section and the second discrete section comprise the same number of light emitting diodes,

the first current is operable to establish a first brightness for the first section; and is also provided with

The second current is operable to establish a second brightness for the second section that is different from the first brightness.

9. A method of emitting light, comprising:

receiving, with a light guide, light from a plurality of light emitting diodes located near an outer edge of the light guide, the outer edge including a first outer edge location;

directing the received light as directed light within a light guide;

directing at least a portion of the directed light out of the light guide through a light emitting surface of the light guide;

reflecting at least a portion of the guided light with a reflective surface of the light guide, the reflective surface being positioned opposite the light emitting surface, the reflected portion remaining as guided light in the light guide,

each of the grooves extends into the reflective surface,

the change in the angle of inclination of the angled surfaces is such that the acute angle between the first surface and the second surface decreases with increasing distance from the first outer edge location,

10. A lighting system, comprising:

a light guide having a circular outer edge;

a plurality of light emitting diodes located near an outer edge of the light guide and configured to direct light inside the light guide as directed light toward a center of the light guide, the outer edge comprising a first outer edge location,

the light guide has a reflective surface opposite the light emitting surface,

each of the grooves extends into the reflective surface,

the first discrete section is configured to produce light having a first brightness,

the second discrete section is configured to generate light having a second brightness, the second brightness being different from the first brightness,

11. The lighting system of claim 10, wherein the first discrete section and the second discrete section comprise different numbers of light emitting diodes.

12. The lighting system of claim 10, further comprising a controller configured to power the discrete sections.

13. The lighting system of claim 12, wherein:

the controller is further configured to provide a first current to the first discrete section and a second current different from the first current to the second discrete section,

a first current is operable to establish the first brightness for the first section, an

The second current is operable to establish the second brightness for the second section.