Asymmetrical light intensity distribution from luminaire
In one embodiment, an overhead street light (a luminaire) is formed that has an asymmetric light intensity distribution, where the peak intensity is greatest along the direction of the street, lower directly across the street, and much lower on the house side of the street. Around the edge of a circular transparent light guide are white light LEDs that inject light into the light guide. To help control the asymmetry of the light intensity distribution, sawtooth-shaped grooves are formed in the light guide surface opposite to the light-emission surface and parallel to the street. Gaussian diffusers are used to partially diffuse the light. By proper selection of the grooves, the Gaussian diffuser, and the relative amounts of light emitted by LED segments around the light guide, the desired asymmetrical light intensity distribution is achieved while a direct view of the light exit surface appears as a uniform light.
1. A lighting system, comprising:
a light guide configured to receive light from a plurality of light-emitting diodes positioned proximate a perimeter of the light guide,
the perimeter including a first perimeter location,
the received light being guidable inside the light guide as guided light,
the light guide having a light-emission surface configured to allow at least a portion of the guided light to exit the light guide through the light-emission surface,
the light guide having a reflection surface opposite the light-emission surface,
the reflection surface 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 reflection surface including a plurality of grooves that extend parallel to one another along the reflection surface,
each groove extending into the reflection surface,
each groove including a first surface that is inclined toward the first perimeter location at a respective angled surface inclination angle,
each groove including a second surface, adjoining the first surface, that is oriented orthogonal to the light-emission surface,
the grooves increasing in depth with increasing distance away from the first perimeter location,
the angled surface inclination angle varying such that an acute angle between the first surface and the second surface decreases with increasing distance away from the first perimeter location,
the second surfaces being configured to reflect light away from the first perimeter location, such that the majority of the light emitted from the light-emission surface is in a direction away from the first perimeter location.
2. The lighting system of claim 1 , wherein:
the light-emission surface includes a plurality of Gaussian diffusive dots printed on the light-emission surface; and
each Gaussian diffusive dot includes a plurality of microbeads disposed in an epoxy-based material, the microbeads having a refractive index different from a refractive index of the epoxy-based material.
3. The lighting system of claim 1 , further comprising a reflector positioned adjacent to and parallel to the reflection surface, the reflector configured to reflect guided light that exits the light guide through the reflection surface back toward the reflection surface.
4. The lighting system of claim 1 , further comprising the plurality of light emitting-diodes positioned proximate the perimeter of the light guide and configured to direct light into the light guide to form the guided light.
5. The lighting system of claim 4 , wherein:
the plurality of light-emitting diodes is divided among discrete segments around the perimeter of the light guide; and
a first of the discrete segments and a second of the discrete segments include different numbers of light-emitting diodes.
6. The lighting system of claim 4 , wherein:
the plurality of light-emitting diodes is divided among discrete segments around the perimeter of the light guide;
the light-emitting diodes in each of the discrete segments are electrically connected in series; and
the discrete segments are electrically connected in parallel.
7. The lighting system of claim 4 , wherein:
the plurality of light-emitting diodes is divided among discrete segments around the perimeter of the light guide; and
further comprising a controller configured to electrically power the discrete segments, the controller configured to supply a first current to a first of the discrete segments and supply a second current, different from the first current, to a second of the discrete segments.
8. The lighting system of claim 7 , wherein:
the first of the discrete segments and the second of the discrete segments include a same number of light-emitting diodes;
the first current operationally establishes a first brightness for the first segment; and
the second current operationally establishes a second brightness, different from the first brightness, for the second segment.
9. A method for emitting light, comprising:
receiving, with a light guide, light from a plurality of light-emitting diodes positioned proximate a perimeter of the light guide, the perimeter including a first perimeter location;
guiding the received light inside the light guide as guided light;
directing at least a portion of the guided light to exit the light guide through a light-emission surface of the light guide;
reflecting at least a portion of the guided light with a reflection surface of the light guide, the reflection surface being positioned opposite the light-emission surface, the reflected portion remaining in the light guide as guided light,
the reflection surface including a plurality of grooves that extend parallel to one another along the reflection surface,
each groove extending into the reflection surface,
each groove including a first surface that is inclined toward the first perimeter location at a respective angled surface inclination angle,
each groove including a second surface, adjoining the first surface, that is oriented orthogonal to the light-emission surface,
the grooves increasing in depth with increasing distance away from the first perimeter location,
the angled surface inclination angle varying such that an acute angle between the first surface and the second surface decreases with increasing distance away from the first perimeter location,
the second surfaces being configured to reflect light away from the first perimeter location, such that the majority of the light emitted from the light-emission surface is in a direction away from the first perimeter location.
10. A lighting system, comprising:
a light guide having a circular perimeter;
a plurality of light-emitting diodes positioned proximate a perimeter of the light guide and configured to direct light inside the light guide toward a center of the light guide as guided light, the perimeter including a first perimeter location,
the light guide having a light-emission surface configured to allow at least a portion of the guided light to exit the light guide through the light-emission surface,
the light guide having a reflection surface opposite the light-emission surface,
the reflection surface 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 reflection surface including a plurality of grooves that extend parallel to one another along the reflection surface,
each groove extending into the reflection surface,
each groove including a first surface that is inclined toward the first perimeter location at a respective angled surface inclination angle,
each groove including a second surface, adjoining the first surface, that is oriented orthogonal to the light-emission surface,
the plurality of light-emitting diodes being divided among discrete segments around the perimeter of the light guide,
a first of the discrete segments configured to produce light having a first brightness,
a second of the discrete segments configured to produce light having a second brightness different from the first brightness,
the grooves increasing in depth with increasing distance away from the first perimeter location,
the angled surface inclination angle varying such that an acute angle between the first surface and the second surface decreases with increasing distance away from the first perimeter location,
the second surfaces being configured to reflect light away from the first perimeter location, such that the majority of the light emitted from the light-emission surface is in a direction away from the first perimeter location.
11. The lighting system of claim 10 , wherein the first of the discrete segments and the second of the discrete segments include different numbers of light-emitting diodes.
12. The lighting system of claim 10 , further comprising a controller configured to electrically power the discrete segments.
13. The lighting system of claim 12 , wherein:
the controller is further configured to supply a first current to a first of the discrete segments and supply a second current, different from the first current, to a second of the discrete segments;
the first of the discrete segments and the second of the discrete segments include a same number of light-emitting diodes;
the first current operationally establishes the first brightness for the first segment; and
the second current operationally establishes the second brightness for the second segment.