Patent Application
20080037259
The present invention relates to luminaires for outdoor lighting and, more particularly, to a positive contrast roadway luminaire and lighting system.
There are two groups that make recommendations and set standards for the lighting of roadways in the United States. These are the Illumination Engineering Society of North America (IESNA) in conjunction with the American National Standard Institute (ANSI), which publishes the American National Standard Practice for Roadway Lighting designated ANSI/IESNA RP-8-2000, and the American Association of State Highway and Transportation Officials (AASHTO), which publishes the “Roadway Lighting Design Guide”. Moreover, the Federal Highway Administration (FHWA) has a manual for roadways, namely The Roadway Lighting Handbook—1978 (revised 1984), that includes lighting as do the fifty states which use it as the basis for their respective state practices. Some states use RP-8 and some use AASHTO, and some states have no written uniform policies, instead leaving lighting practice up to district offices. The FHWA has a policy of funding projects that use the AASHTO guide or ANSI/IESNA RP-8. The criteria for lighting freeways do not differ significantly between RP-8 and AASHTO for the Illuminance or Luminance Methods.
One of the major criteria recommended by both groups is the “full cutoff” requirement. This establishes limits on light emitted vertically from the luminaire to minimize “skyglow.” Skyglow is the result of light directed upward into the atmosphere and is an undesired effect of outdoor lighting. It consists both of light from the luminaire that is reflected by the ground or other structures, as well as the direct light from the luminaire directed outward at near-horizontal angles and upward. “Full cutoff,” as defined by IESNA, requires that there be no direct light from the luminaire at or above the 90° vertical angle and no more than 10% of the lamp lumens at or above 80° vertical angle. This is interpreted by reviewing the candlepower distribution table of a photometric report of the luminaire and not finding any candlepower value in the angle ranges greater than 10% of the rated lamp lumens. For example, if a 400 watt HPS lamp is rated 50,000 lumens, then a candlepower value of 5000 or more at or above 80° vertical angle in any lateral plane would exceed the limit for this classification.
Conventional roadway lighting systems include roadway luminaires that provide a bisymmetric lighting distribution. This means that an equal amount of light is projected from the luminaire upstream and downstream of the traffic flow on the roadway. In other words, there is a light distribution symmetry about a plane perpendicular to the axis of the roadway. However, this light distribution results in glare and alternating areas of positive (in the direction of traffic) and negative (against the direction of traffic) light contrast.
Another standard practice is to space lighting poles at four to six (4-6), and more typically five (5), “mounting heights.” As the term implies, “mounting height” is the height above ground at which the luminaire of the light pole is mounted. Thus, if the common mounting height is 40 feet above ground, the spacing between poles will typically be 160-240 feet. Typical mounting arrangements for roadway poles include single roadside arrangements, staggered double-sided arrangements, opposite double-sided arrangements and median mounted arrangements.
It is also important to light the right hand edge of the road to help the driver keep his vehicle on the road and to help identify exit and entrance ramps, as well as merging traffic. Slower traffic having mechanical problems typically travel to the right and animal and pedestrian intrusion also occurs in this area. For these reasons it is desirable for the luminaire to target light on the two most right hand lanes and the breakdown lane and let spill light take care of the inner lanes.
Other standard criteria for lighting roadways include minimum maintained average values for illuminance, luminance and Small Target Visibility (STV in RP-8). Each of these has a uniformity requirement as well as a requirement for comparing the average to the minimum and the maximum to the minimum. There also exists a glare measure called the veiling luminance ratio. This compares the cumulative contribution of the luminance of all of the luminaires to the background scene or pavement luminance.
Accordingly, it would be desirable to provide a roadway lighting system that meets as many of the illuminance, luminance, STV, uniformity, glare, full cutoff, spacing and utilization criteria as possible. It is also desirable to provide a system utilizing a “Positive Contrast” light distribution to improve visibility, complement vehicle headlights and minimize glare to the driver during the driving task, wherein the targeted veiling luminance ratio is 0.20:1.0 or less.
It would further be preferable to provide a luminaire having a size and shape that conforms to products that are currently on the market so as to blend in when used as a replacement in existing installations. The overall weight and EPA of the luminaire should be similar as well so as to not exceed ratings for existing poles and arms and to permit the retrofitting of luminaires with better performing, energy saving replacements.
The present invention is a luminaire assembly providing asymmetric, positive contrast lighting. The luminaire generally includes a reflector having a center of symmetry and a lamp supported within the reflector, wherein the lamp is offset from the reflector center of symmetry, whereby light emitted from the lamp is reflected by the reflector in an asymmetric pattern.
In a preferred embodiment, the reflector includes a plurality of curved reflective bands arranged coaxially in decreasing radial size order along a central z-axis beginning at a central x-y plane, wherein the central z-axis intersects the central x-y plane to define the center of symmetry. The curved bands can be circular to form a spherical reflector, elliptical to form an elliptical reflector or oval to form an ovoid reflector.
In the case of a spherical reflector, the reflector has a maximum diameter at the central x-y plane and a height along the central z-axis from the central x-y plane to a reflective top surface. The lamp is then preferably offset from the center of symmetry in an x-direction a distance of about one-third (⅓) the maximum diameter. The lamp is also preferably offset from the center of symmetry in a y-direction a distance of about one-twentieth ( 1/20) the maximum diameter and in a z-direction a distance of about one-eighth (⅛) the height.
In the case of an elliptical reflector, the reflector has a maximum minor axis dimension in an x-direction and a maximum major axis dimension in a y-direction at the central x-y plane and a height along the central z-axis from the central x-y plane to a reflective top surface. The lamp is then preferably offset from the center of symmetry in the x-direction a distance of about one-fourth (¼) the maximum minor axis dimension. The lamp is also preferably offset from the center of symmetry in the y-direction a distance of about one-fifteenth ( 1/15) the maximum major axis dimension and in a z-direction a distance of about one-eighth (⅛) the height.
In the case of an ovoid reflector, the curved reflective bands preferably include four elliptically shaped arc segments defining an oval. The arc segments preferably include a first arc segment defined by a minor axis in the x-direction and a major axis in the y-direction and a second arc segment defined by a minor axis in the x-direction and a major axis in the y-direction, wherein the minor axes for the first and second arc segments are equal, and wherein the major axis for the first arc segment is greater than the major axis of the second arc segment. Also, the arc segments can be truncated in the x-direction so that said reflective band has a width less than the minor axes.
In all of the above described embodiments, the reflector can include a circumferential edge defining a reflector opening plane, wherein the reflector opening plane is disposed at an angle with respect to the central x-y plane. In addition, the luminaire can further include a planar lens plate disposed adjacent the reflector opening, wherein the planar lens plate is disposed at an angle with respect to the central x-y plane.
The present invention further involves a method for illuminating a roadway having traffic moving in a flow direction. The method generally includes the steps of mounting a luminaire having a reflector and a lamp at a side of the roadway and reflecting light emitted from the lamp with the reflector whereby a greater portion of the emitted light is directed in the traffic flow direction than is directed against the traffic flow direction.
In a preferred embodiment, the luminaire is mounted on a side of the roadway, and the method further includes the step of reflecting light emitted from the lamp with the reflector whereby a greater portion of the reflected light is directed in a direction away from a house side of the roadway than is directed toward the house side.
Also, the luminaire is preferably mounted above the roadway at a mounting height and the greater portion of the reflected light is directed in the traffic flow direction a distance equal to about four to five (4-5) times the mounting height and the portion of the reflected light directed in the opposite direction against the traffic flow direction is directed a distance equal to about one to two (1-2) mounting heights. Moreover, the greater portion of the reflected light is directed in the traffic flow direction at an angle of between sixty to seventy-six degrees (60°-76°) from vertical.
In another method for illuminating a roadway having traffic moving in a flow direction, a luminaire is mounted at an angle with respect to the roadway such that a greater portion of light emitted from the luminaire is directed in the traffic flow direction than is directed against the traffic flow direction. Light emitted from the luminaire is prevented from traveling against the traffic flow direction with a shield.
In another aspect of the present invention, an optical assembly for mounting in a luminaire is provided. The optical assembly generally includes a reflector having a center of symmetry and a lamp supported within the reflector, wherein the lamp is offset from the reflector center of symmetry in all axes, whereby light emitted from the lamp is reflected by the reflector in an asymmetric pattern.
In a preferred embodiment, the reflector includes an opening and the optical assembly further includes a reflector hood disposed at the reflector opening for directing light in the asymmetric pattern. The reflector hood restricts light emitted from the lamp at eighty degrees (80°) vertical and above on a direction of traffic side of the optical assembly and at fifty degrees (50°) vertical and above on an opposite side of the optical assembly.
The reflector hood preferably includes a ring portion and a bill portion extending from the ring portion. The ring portion has a size and shape adapted to fit on the opening of the reflector and the bill portion extends outwardly therefrom in a radial direction and is angled downward in the axial direction. The reflector hood can also be made adjustable with respect to the reflector for directing light in the desired asymmetric pattern.
A preferred form of the roadway luminaire and method for illumination, as well as other embodiments, objects, features and advantages of this invention, will be apparent from the following detailed description of illustrative embodiments thereof, which is to be read in conjunction with the accompanying drawings.
Referring first to
The luminaire housing 12 can be of any shape or configuration and is adapted to mount to a light pole (not shown). The housing is preferably made from a die cast aluminum and has a minimum wall thickness of 0.093″. In a preferred embodiment, the housing 12 has a “cobra-head” style since such is the most common style found in conventional roadway luminaires. In general, the light pole will be positioned offset from the side of a roadway, wherein light is distributed up the road in the direction of traffic 35, down the road in a direction against traffic 37, perpendicularly across the road in a “street side” direction 36 and back toward the pole in a “house side” direction 38.
The reflector 14 includes a radially symmetrical dome portion 20, a bracket portion 22 and a base portion 24. The dome portion 20 is preferably made from a pre-finished highly specularly reflective aluminum in a conventional manner. For example, a pre-finished specular aluminum sheet can be cut to a pattern, then formed and fastened together. Another method is to spin the profile using conventional metal spinning techniques and then polishing and finishing the interior surface to get the necessary performance. A third method is to mold the reflector surfaces and vacuum-metalize them with pure aluminum to provide the necessary performance.
The dome portion 20 is radially symmetrical and defines a circular opening 21 through which light emitted from the lamp assembly 16 exits. The dome portion 20 includes a plurality of horizontally arranged reflective bands 28 for directing the light out of the opening 21 in a desired direction. Beginning at the opening 21, the bands 28 forming the bottom-half portion of the dome 20 are preferably about one-half inch (0.5″) in width. At about the mid-way point of the height of the dome 20, the bands 20 preferably increase in width to about one inch (1.0″). The bands terminate at a circular disk portion 23 disposed at the top of the dome portion.
Each band 28 may be in the form of a continuous circular band, or, more preferably, each band is segmented and consists of a plurality of rectangular shaped reflective facets 28a connected end-to-end to form a substantially circular band. Preferably, each band 28 consists of about sixty (60) rectangular segments or facets 28a. The rectangular facets 28a preferably have a length of about one inch (1.0″) in the band 28 defining the opening 21 of the reflector 14 and gradually decrease in length in each successive band approaching the circular disk 23 at the top of the dome portion 20. It has been found that the rectangular segments or facets 28a send out individual beams of light that intersect each other creating better uniformity.
The rectangular facets 28a can define flat reflective surfaces or the reflective surfaces of the facets can be formed with a curve of non-constant radius. Thus, the midpoints of the bands can be connected with a curve of non-constant radius. This produces a smooth surface and reduces the possibility of manufacturing defects.
The bracket portion 22 is attached to both the top of the dome portion 20 and the base portion 24 to provide strength and stability to the reflector portion. The base portion 24 is generally a flat plate adapted to mount within the luminaire housing 12. The base portion 24 may further be provided with structure (not shown) for mounting the flat lens plate 18 thereto.
The lamp assembly 16 generally includes a lamp 30 and lamp socket 32. Electrical wiring (not shown) is connected to the lamp socket 32 in a conventional manner to provide power to the lamp 30. In a preferred embodiment, the lamp 30 is a 150-250 watt high pressure sodium (HPS) lamp. As will be discussed in further detail below, the present invention allows for the use of lower wattage lamps, as compared to the standard 310-400 watt lamps, although standard wattage lamps can be used in the present invention as well. The HPS lamp is preferred due to the geometry of its arc tube and its light emitting portion. The center 31 of the lamp 30 is defined as the mid-point of the arc tube along the longitudinal axis of the lamp.
The lens plate 18 is generally a flat glass plate, which can be mounted flush with the opening of the dome portion 20 of the reflector 14. Of course, other durable materials, as is known in the art, may also be used. Gaskets or other seals (not shown) are preferably provided between the lens plate 18 and the base portion 24 of the reflector 14 and/or the luminaire housing 12 to prevent moisture or other contaminants from entering the dome portion 20 of the reflector.
In a preferred embodiment, the lens plate 18 is mounted to the reflector 14 at an angle with respect to the opening of the dome portion 20, as shown in
Part of the present invention lies in the positioning of the lamp assembly 16 within the reflector 14. Unlike conventional luminaires, the lamp assembly 16 of the present invention is offset from the center of the reflector 14. Based on an X,Y,Z Cartesian coordinate system oriented at the radial center 34 of the dome portion 20, wherein the x-axis is parallel to the roadway, the y-axis runs perpendicularly across the roadway and the z-axis extends vertically away from the roadway, the lamp assembly 16 is offset a pre-determined distance in all three directions. Specifically, the center 31 of the lamp 30 is offset a distance “a” from the dome center 34 along the x-axis in a direction against the flow of traffic 35 on the roadway, along the y-axis a distance “b” in a direction toward the “house side” 36 of the luminaire and along the z-axis a distance “c” in a direction upward into the dome portion 20. As will be discussed further below, this positioning of the lamp assembly 16 within the reflector 20 results in a greater proportion of light being directed up the roadway in the direction of traffic (i.e., positive contrast lighting), as well as a greater proportion of light being directed in the “street side” 36 direction across the roadway, and less on the “house side” 38.
It has been found that best photometric results are achieved by shifting the center 31 of the lamp 30 in the x-direction a distance of about one third (⅓) the maximum diameter of the dome portion 20 and in the y-direction a distance of about one twentieth ( 1/20) the maximum diameter of the dome portion. The center 31 of the lamp 30 is also preferably positioned above the center 31 in the z-direction at a distance of about one eighth (⅛) the distance from the center to the top of the dome.
Using specific dimensions, it has been found that a dome portion 20 having a diameter of about twenty inches (20.0″), a height of about eight inches (8.0″) above the center 34 and a disk portion 23 having a diameter of about five inches (5.0″) produces the best photometric results. This means that the lamp assembly 16 will be offset from center 34 in the x-direction about 6.5″ and in the y-direction about 1.0″. Also, the lamp 16 is then spaced a distance of about 1.0″ above the center 34 in the z-direction.
As shown in
With the lamp assembly 16 thus positioned, the reflective bands 28 are designed to reflect light emitted from the lamp at an optimum angle down the road in the direction of traffic 35 to provide the maximum contrast lighting benefit. It has been found that the optimum angle for directing light up the roadway is between sixty and seventy-six degrees (60°-76°), and more preferably between about seventy-two degrees and seventy-six degrees (72°-76°), as shown in
This lamp positioning also allows a portion of the light emitted from the lamp assembly 16 to be directed at optimum angles up the road in the opposite direction 37 against traffic. It has been found that the optimum angle for this “upstream” light is between zero and about fifty degrees (0°-50°). Light emitted at a higher angle against the flow of traffic is more likely to shine directly in the eyes of drivers and create a safety hazard.
Finally, by positioning the lamp assembly 16 as described, light rays 40 emitted from the lamp 30 that strike the opposite far half of the reflector dome portion 20 are reflected back and impinge on the near half of the reflector dome portion and are, in turn, directed “downstream” 35 in the direction of traffic at the optimum angle of between about 72°-76°. Thus, most of the light emitted from the lamp assembly 16 is directed downstream to provide maximum positive contrast lighting.
To achieve the optimum “downstream” angle, each reflective band 28 is individually angularly oriented to reflect light hitting the respective band at the optimum angle.
The luminaire 10 thus far described and shown in
Turning now to
Alternatively, to reduce the size of the reflector further while maintaining improved light reflection, a reflector 52a can be made having an egg, ovate or ovoid shape from a series of reflective bands 62a that are not true ellipses, as shown in
In the case of the true elliptical reflector 52 shown in
Like the spherical reflector 20 described above, the elliptical reflector 52 includes a plurality of horizontally arranged reflective bands 62, for directing the light out of the opening 58 in a desired direction, which terminate at an elliptical reflective surface 64 disposed at the top of the reflector. Again, each band 62 may be in the form of a continuous elliptical band, or, more preferably, each band is segmented and consists of a plurality of rectangular shaped reflective facets connected end-to-end to form a substantially elliptical band, as described above. However, with the smaller elliptical reflector 52, since the reflective surfaces are closer to the lamp center 31, it is necessary to reduce the band width to 0.25 inches in order to sufficiently control the light distribution.
In the case of the ovoid shaped reflector 52a shown in
Also like the spherical reflector 20 described above, both the elliptical reflector 52 and the ovoid reflector 52a are designed to be positioned offset from the side of a roadway, wherein light is distributed up the road in the direction of traffic 35, down the road in a direction against traffic 37, perpendicularly across the road in a “street side” direction 36 and back toward the pole in a “house side” direction 38. In this case, the minor axes 60 of the elliptical and ovoid reflectors 52 extend parallel with the road and the major axes 61 extend generally perpendicular to the road direction.
Again, the center 31 of the lamp (not shown in
With the elliptical reflector 52, it has been found that best photometric results are achieved by shifting the center 31 of the lamp in the x-direction a distance of about one fourth (¼) the length of the minor axis of the largest ellipse adjacent the opening 58 and in the y-direction a distance of about one fifteenth ( 1/15) the length of the major axis of the largest ellipse adjacent the opening. The center 31 of the lamp is also preferably positioned above the center 54 in the z-direction at a distance of about one eighth (⅛) the distance from the center to the top of the reflector.
Using specific dimensions, it has been found that an elliptical reflector 52 having a maximum major axis of about fifteen inches (15.0″), a maximum minor axis of about twelve inches (12.0″) and a height above the design center 54 of about six inches (6.0″) produces the best photometric results. This means that the center 31 of the lamp assembly will be offset from the reflector center 54 in the x-direction about 3.0″ (a dimension) and in the y-direction about 1.0″ (b dimension). Also, the lamp center 31 is then spaced a distance of about ¾″ (c dimension) above the reflector center 54 in the z-direction.
With the lamp center 31 thus positioned, the reflective bands 62 are designed to reflect light emitted from the lamp at an optimum angle down the road in the direction of traffic 35 to provide the maximum positive contrast lighting benefit. This lamp positioning also allows a portion of the light emitted from the lamp assembly to be directed at optimum angles up the road in the opposite direction 37 against traffic. As described above, the optimum angle for directing “downstream” light up the roadway in the direction 35 is between about seventy-two degrees and seventy-six degrees (72°-76°), and the optimum angle for directing “upstream” lights up the road in the opposite direction 37 against traffic is between zero and about fifty degrees (0°-50°).
The profile from the light source to the reflector 52 and then from the reflector to the roadway is illustrated by the ray tracings shown in
As can be appreciated, with the opening 58 thus angled, the lens plate 18 can be disposed directly against the edge of the reflector 50, as shown in
With the reflector opening 58 tilted an angle to allow light out at higher vertical angles on the pro side, the reflector 50 further preferably includes a reflector hood 70, as shown in
In this regard, the hood 70 resembles a visor having a ring portion 72 and a bill portion 74 extending from the ring portion. The ring portion 72 has a size and shape adapted to fit on the opening edge 65 of the reflector 50 and the bill portion 74 extends outwardly therefrom in a generally radial direction and is also angled slightly downward in the axial direction. When attached to the reflector 50, the bill portion 74 extends in the traffic flow direction 35 and is angled downward from the horizontal plane 59 at about a seventy-two to seventy-six degree (72°-76°) angle so as to prevent any light at an angle above about eighty degrees (80°) from exiting the reflector. Similarly, the ring portion 72 prevents any light above fifty degrees (50°) vertical from exiting the reflector. The hood 70 can be made from any durable material adapted for external environments and can be attached to the reflector 50 in any conventional manner.
Whereas it may be desirable to rotate the luminaire 10 about its axis or the optical assembly 12 or 50 within the luminaire about its axis to distribute more light in the direction of flow of traffic 35 and less light counter to traffic flow 37, or vice-versa, a means of adjusting the luminaire 10 or optical assembly 12 or 50 can be provided. Moreover, the visor 70 can also be provided with a means of adjustment to adjust the visor with respect to the reflector in order to shield any undesired upward light (i.e., light above eighty degrees (80°) vertical in the traffic flow direction and light above fifty degrees (50°) vertical in the direction against traffic). In this regard, the visor 70 can be made adjustable with respect to the reflector as a whole, or the ring portion 72 may be adjusted independently of the bill portion 74. This can be accomplished by providing, for example, a thumb screw and a protractor attached at the centerpoint between the ring and bill of the shield. The thumb screw would be loosened and the shield adjusted to a vertical angle using the protractor attached under the screw. The vertical angles could be provided in a table in a user's guide furnished with the system.
With any of the spherical reflector 20, the elliptical reflector 52, or the ovoid reflector 52a, the luminaire of the present invention provides an asymmetric, positive contrast light distribution providing improved visibility with virtually no glare. This is also achieved while maintaining a five mounting height (5 MH) distance between adjacent luminaires 10, as shown in
Tables 1 and 2 below set forth the performance characteristics of the positive contrast lighting system (PCLS) of the present invention as compared to several selected conventional roadway lighting systems using a 250 W HPS lamp and a 150 W HPS lamp.
Eavg = Illuminance
Eavg/min = Illuminance Uniformity
Lavg = Luminance
Lavg/min = Luminance Uniformity
Lmax/min = Luminance Uniformity
Lvmax/Lpavg = Veiling Luminance
STV = Contrast
Spacing = 200′, Mounting Height = 40′, −5′ Overhang, Total Road Width = 24′, LLF = 0.72
Values of E in FC, L in cd/m2
All systems are Full Cutoff
As a result of the present invention, a positive contrast roadway lighting system is provided having an asymmetric light distribution providing improved visibility with virtually no glare. The system meets IESNA RP-8-2000 and AASHTO freeway lighting requirements and also meets a Mounting Height ratio of 5:1 or better for luminaire pole spacing. The system of the present invention improves visibility with positive contrast and reduces skyglow both directly, by the luminaire achieving full cutoff, and indirectly, by reducing amount of light between 0-60° vertical. Also, the roadway lighting system of the present invention saves energy by providing better lamp utilization and light output at higher vertical angles.
Moreover, the low profile, elliptically shaped housing of the luminaire of the present invention results in low EPA (effective projected area) and the optics can be adjusted for setback compensation and the main aiming beam can be adjustable. The housing can further be provided with positive latching for secure closure and a 4-bolt fitter clamp with positive stop and can be easily removable with adaptive hinging and a capture screw. The luminaire can further be provided with leveling means to provide adjustment of between ±7.5° and is gasketted to meet an IP66 rating for dust and watertight operation.
Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be effected by one skilled in the art without departing from the scope or spirit of the invention.
This application claims the benefit of U.S. Provisional Application No. 60/837,221, filed on Aug. 11, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60837221 | Aug 2006 | US |
