Patent Publication Number: US-8118456-B2

Title: Low-profile pathway illumination system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 61/051,619, filed May 8, 2008, entitled “Low-Profile Pathway Illumination System”, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure generally relates to an illumination system and more particularly to a low-profile pathway illumination system. 
     2. Description of the Related Art 
     Pathway lighting is important for safety and security reasons and, in some cases, for aesthetic reasons as well. In general, existing pathway lights can be grouped into three main classes: bollards and overhead lighting systems that are installed on poles or walls, lighting systems mounted close to the ground, and “paver lights” installed in a pathway surface. Further, pathway lights can be divided into low voltage and mains voltage lighting systems. 
     Overhead and bollard lighting systems are typically robust and permanent, but tend to have relatively high costs of installation and maintenance. These lighting systems are typically powered by the mains voltage and typically require expensive waterproof conduits, concrete support bases and careful planning to install. Professional contractors are usually required to install these lighting systems. Besides, the electronic controls, sensors and timers required for their operation are expensive and must be installed by licensed electricians. Overhead and bollard lighting systems also tend to detract from the aesthetics of the architecture, landscaping and natural features where they are sited. In some cases, both the luminaires and the light they emit block the view of the carefully designed environment that they are lighting, and greatly detract from the visual enjoyment of the site. 
     There are also lighting systems that are mounted close to the ground or pathway that they illuminate. These near-ground lighting systems, however, may be less robust as they tend to suffer from the small size of their mountings. In addition, a greater quantity of these small lights is typically required to properly illuminate a pathway relative to, for example, bollards or overhead lighting. Maintenance costs associated with these small, near-ground lighting systems can be high because of the large number of lamps that eventually need replacement, physical damage to the more delicate luminaires, and the close proximity of the luminaires to lawn maintenance equipment and pathway traffic. While aesthetically more pleasing than overhead lights or bollards, these near-ground lighting systems also detract from a well-designed space, cluttering the pathway with fragile-looking luminaires. 
     Paver lights, lights that are installed in the pathway surface, typically provide little or no illumination of the pathway surface and are used primarily for the purpose of delimiting the pathway. These lights tend to be difficult to install and maintain because they are designed to be embedded in the pathway surface material. Installation is especially difficult and expensive if paver lights are to be installed into existing concrete sidewalks. Additionally, power wires must be run under the pathway, further making them difficult and expensive to install and maintain. Moreover, because typical paver lights emit almost all of their light upwards into the sky, they do not always illuminate potentially dangerous objects left on the pathway or other hazards on the pathway. Worse yet, paver lights may obscure the presence of potential hazards by shining upwards into a pedestrian&#39;s eyes. 
     An important concern with pathway lighting is the grounds maintenance costs associated with mowing and weed-removal activities around each luminaire. In the case of overhead or bollard lights, a very real danger exists of collision from riding lawn mowers, maintenance trucks and carts, or from individuals engaged in sports or other activities. Near-ground pathway lights are very costly to mow or weed around, and may easily be damaged in the process. They also present a hazard to pedestrians who may trip over or onto the relatively short luminaires. 
     There is, therefore, a need for a lighting system that is relatively easier and less costly to install and replace compared to the existing pathway lighting systems, and has a low profile to minimize danger from collision and tripping as well as detraction with the aesthetics of the site. 
     BRIEF SUMMARY 
     A luminaire to illuminate surfaces may be summarized as including a housing including a base having a bottom surface that is positionable on a surface to be illuminated, the housing including an interior and at least one window providing access between the interior of the housing and an exterior of the housing; a mounting fixture extending at least approximately perpendicularly downward with respect to the bottom surface of the base to secure the housing to a peripheral portion of the surface to be illuminated; and a light source received in the interior of the housing, the light source having a principal axis of emission that is directed outwardly through the window of the housing at a downwardly oriented angle with respect to the bottom surface of the base such that, when in use with the luminaire mounted to the surface to be illuminated, the principal axis of emission of the light source is directed at a portion of the surface to be illuminated. 
     The mounting fixture may include at least one mounting hole sized to receive a portion of a respective fastener. The base and the mounting fixture may each be separate unitary parts that are physically coupled together. The light source may include at least one light emitting device. The light source may include at least one solid-state light emitting device. The light source may include at least one light-emitting diode. The luminaire may further include a controller coupled to regulate power to the light source. The controller may be configured to regulate power at a voltage level within a threshold from a voltage level of a power source to permit full light emission by the light source. The controller may be configured to regulate power to the light source to adjust an intensity of the light emitted by the light source according to a voltage of power from a power source. The luminaire may further include a controller housing physically coupled to the mounting fixture, the controller housing having an interior in which the controller is received, wherein the housing, the mounting fixture and the controller housing each includes at least one respective passage to provide communication between the controller in the interior of the controller housing and the light source in the interior of the housing. The window may include a substantially transparent member positioned in an opening of the housing to environmentally isolate the interior of the housing from the exterior thereof. The substantially transparent member may be a toughened glass made of one of Chrysterna and Pyrex. The substantially transparent member may be coated with one of artificial diamond-like deposition and sapphire. The window may have a shape that forms the light emitted by the light source into a light beam when exiting the housing, the light beam having a vertical angle of +/−10 degrees relative to a horizontal plane parallel to the surface to be illuminated and a horizontal angle of at least +/−70 degrees along the horizontal plane. The housing may have a height of less than 0.75 inch measured from the surface when positioned on the surface to be illuminated. The interior of the housing may be environmentally sealed from the exterior thereof. A top portion of the interior of the housing, at least partially between the light source and the window, may have high reflectance, and wherein a bottom portion of the interior of the housing, at least partially between the light source and the window, may have low reflectance. 
     A pathway light may be summarized as including a solid-state device configured to emit light when powered; a control circuit coupled to the solid-state device and a power input, the control circuit configured to receive power from the power input and provide regulated power to the solid-state device; and a housing for enclosing the solid-state device and the control circuit, the housing constructed to withstand contact by moving equipment and function as a heat sink for the solid-state device and the control circuit, the housing having an opening shaped and angled to project light emitted by the solid-state device onto and across a surface to be illuminated when the pathway light is placed on the surface in a position for operation. 
     The solid-state device may include at least one light-emitting diode. The housing may have a height of less than 0.75 inch measured from the surface when placed on the surface in the position for operation. The control circuit may include a low dropout voltage regulator configured to adjust an intensity of the light emitted by the solid-state device according to a voltage level of the power from the power input. The housing may be at least partially placed on the surface when the pathway light is in operation, and wherein the housing may have a maximum height of less than 0.75 inch measured from the surface when the housing is placed on the surface. The housing may further have an extension that extends from the housing in a direction such that when the pathway light is in the position for operation with the extension inserted into a discontinuity in the surface or into a gap between the surface and an adjacent surface the light from the solid-state device is projected onto and across the surface through the opening of the housing. The pathway light may further include a hardened glass that is substantially transparent and placed in the opening of the housing to protect the solid-state device from moisture and physical damage, and wherein the hardened glass is coated with one of artificial diamond-like deposition and sapphire for extended life. The opening of the housing may form the light emitted by the solid-state device into a light beam having a vertical angle of +/−10 degrees relative to a horizontal plane parallel to the surface to be illuminated and a horizontal angle of at least +/−70 degrees along the horizontal plane. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1A  is a front elevational view of a pathway light according to one non-limiting illustrated embodiment. 
         FIG. 1B  is top plan view of a pathway light of  FIG. 1A . 
         FIG. 1C  is a side elevational view of the pathway light of  FIG. 1A . 
         FIG. 2  is an isometric view of the pathway light of  FIG. 1A . 
         FIGS. 3A-3B  are each a diagram illustrating a pathway light in use according to one non-limiting illustrated embodiment. 
         FIG. 4  is a schematic diagram of a controller circuit of a pathway light according to one non-limiting embodiment. 
     
    
    
     In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings. 
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with lighting fixtures, power generation and/or power systems for lighting have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments. 
     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as “comprises” and “comprising,” are to be construed in an open, inclusive sense that is as “including, but not limited to.” 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
       FIG. 1A  shows a luminaire in the form of a pathway light  10  according to one non-limiting illustrated embodiment. The pathway light  10  comprises a light source housing  20  and a controller housing  30  for enclosing the electrical components of the pathway light  10 . As shown in  FIG. 1A , a light source, which may be a solid-state device such as a light-emitting diode (LED) device  50 , is housed in the light source housing  20  while electronics that control the light source, such as controller  60 , is housed in the controller housing  30 . Alternatively, the pathway light  10  may have a single, unitary housing (not shown) in which both the light source and electronics are contained. Unless otherwise specified, in the following description the word “housing” refers to the light source housing  20  and the controller housing  30  in embodiments similar to that shown in  FIG. 1A , and refers to the single housing that contains both the light source and the electronics that control the light source in other embodiments. 
     In one embodiment, the light source may comprise the LED device  50 , which may include one or more LEDs, such as an array of LEDs. In an alternative embodiment, the light source may be another type of solid-state lighting, such as one or more organic light-emitting diodes or polymer light-emitting diodes. The quantity and color of LEDs in the LED device  50  depend on the intensity and color of light desired. In one embodiment, the LED device  50  comprises a number of LEDs combined together to form a long and narrow light emitter to produce white light with intensity strong enough to illuminate at least a portion of a pathway proximate to where the pathway light  10  is installed. 
     The housing has an opening, e.g., a window  28 , through which light emitted by the LED device  50  can exit the housing. A substantially transparent member  22  is fitted in the window  28  of the housing to protect the LED device  50  from moisture and physical damage (e.g., due to weed removal string trimmers, rocks, sand). The window  28  is shaped and angled so that the resultant light beam projected from the pathway light  10  through the window  28  has a desired shape and is projected at a desired angle. In one embodiment, the light beam is very narrow in a vertical axis with respect to the plane of the pathway to be illuminated and very broad in a horizontal axis parallel with the plane of the pathway, and the light beam is oriented at an angle such that the light beam is projected onto and across the pathway. In this way, the pathway is well illuminated over a wide area in front of the pathway light  10 . In an embodiment, when mounted to a pathway, the bottom surface of the housing of the pathway light  10  is approximately parallel with the top surface of the pathway to be illuminated. In one embodiment, as shown in  FIG. 1B , the light source has a principal axis of emission that is directed outwardly through the window  28  at a downwardly oriented angle with respect to the bottom surface of the housing such that the principal axis of emission of the light source is directed at a portion of the surface to be illuminated. In one embodiment, the light beam exits the housing at a vertical angle of +/−10 degrees in the vertical axis, and an angle of +/−70 degrees in the horizontal axis. 
     An interior channel exists in the housing between the window  28  and the light source. In one embodiment, the interior channel has a narrow shape that confines the light output to a wide aspect-ratio beam. In one embodiment, the bottom portion of the interior channel is coated or covered with a low-reflectance material (e.g., flat black anodizing, or light absorber  26 ) to reduce upward glare, and the top portion of the interior channel is coated or covered with a high-reflectance material (e.g., aluminum mirror  24 ) to help increase the light projected through the substantially transparent member  22 . The substantially transparent member  22  permits high transmission of light out of the pathway light  10  but prevents water or other foreign matter from entering the housing. In one embodiment, the substantially transparent member  22  is hardened or toughened glass, which may be coated with an abrasion resistant coating. In one embodiment, toughened glass such as Chrysterna or Pyrex may be used for the substantially transparent member  22 , and coatings of artificial diamond-like deposition or sapphire may be applied to extend the useful life of the substantially transparent member  22 . 
     The housing of pathway light  10  is preferably watertight to eliminate damage from or entry of moisture due to lawn watering, rain, pressure washing, etc. The housing is preferably constructed to be very rugged and can withstand direct contact or impact by moving equipment. For example, the housing should be very rugged to allow the wheels of lawnmowers, trucks and carts to drive over the pathway light  10  without causing damage to the pathway light  10  or the vehicle&#39;s tires. The outer contour of the housing is shaped in a way to eliminate sharp edges or corners to minimize the chance of tripping a pedestrian or catching a moving object. As best illustrated in  FIGS. 1C and 2 , a portion of the housing of the pathway light  10  includes a bottom surface  12  and a top surface  14  having a pair of portions  14   a ,  14   b  that slope toward the bottom surface  12  from an intermediate portion  14   c . The material which the housing is made of is preferably chosen so that not only the housing is rugged but may additionally function as a heat sink to allow the heat generated by the light source (e.g., the LED device  50 ) and electronics (e.g., the controller  60 ) to be transferred to the ambient environment by conduction, convection and radiation via the housing. For example, aluminum or another metal or alloy may be employed. Additionally, the pathway light  10  is sealed using silicone, epoxy or other sealing material. 
     The pathway light  10  further comprises a mounting fixture  40  (e.g., bracket or plate) for mounting the pathway light  10 . The mounting fixture  40  may be a unitary part of the housing or a separate part assembled together with the housing. In one embodiment, the mounting fixture  40  may be a mounting plate that extends vertically downward from the housing. Alternatively, the mounting fixture  40  may be in another shape and/or extend from the housing in another direction, such as in a horizontal direction. The light source, such as the LED device  50 , may be mounted to the mounting fixture  40 . The mounting fixture  40 , together with the housing, may serve as a heat sink for both the light source and the electronics. 
     Various methods may be used to affix the pathway light  10  to the pathway, sidewalk or whatever surface the luminaire is used to illuminate. In one embodiment, with the mounting fixture  40  being a mounting plate, the pathway light  10  can be relatively easily mounted by inserting the mounting fixture  40  into a discontinuity in the pathway surface, such as a slot or a crevice, or into a gap between an edge of the pathway and an edge of an adjacent surface, such as lawn, gravel ground, dirt ground, pavement, etc. In another embodiment, the pathway light  10  may be affixed by using a bolt through the mounting fixture  40  that is shaped like a plate with a hole  65  ( FIG. 2 ) in it. In an alternative embodiment, adhesive material for bonding may be used. A high-quality polyurethane concrete adhesive is a preferred adhesive material when the pathway light  10  is to be affixed to concrete. In yet another embodiment, a combination of a bolt and adhesive material may be used. In any event, because the pathway light  10  is affixed to the pathway via the mounting fixture  40 , no poured concrete base is needed as with bollards or overhead lights, and, rather, mounting fixture  40  allows the pathway light  10  to be relatively easily installed and removed. 
     When installed at the level of the pathway or sidewalk, the pathway light  10  has a very low profile in that the top of the housing has a height of less than a particular dimension such that the low profile enables lawn mowers, trucks and carts to pass directly over the pathway light  10 . In one embodiment, the height of the housing is less than 0.75 inch to reduce the possibility of pedestrians tripping on the housing. In some states in the United States, the height of 0.75 inch is considered the maximum acceptable safe height for protuberances on walkways. 
     By installing the pathway light  10  at the level of the surface to be illuminated, the aforementioned problems with overhead and near-ground pathway lights are reduced or eliminated. Because of the low profile of the pathway light  10 , pedestrians, law mowers, trucks and carts can pass directly over the luminaire, and the danger of collision or tripping is substantially reduced. The costs associated with installation and maintenance are lower, compared to the costs for installing and maintaining bollards, overhead lighting or near-ground lighting, as pathway light  10  can be relatively easily installed and removed. Further, by projecting light directly onto and across the pathway or sidewalk, the pathway light  10  has much less impact on the aesthetic perception of the environment and is “dark sky” friendly due to its illumination being confined substantially to the pathway surface. The use of a solid-state device for illumination reduces energy consumption versus incandescent or other traditional light sources by as much as 80%. 
       FIG. 2  is an isometric view of the pathway light  10  according to a non-limiting illustrated embodiment. As shown, the mounting fixture  40  is a mounting plate with a hole  65  in it for mounting with a bolt. The housing has a long and very narrow window  28  that allows a light beam long in the horizontal axis and very narrow in the vertical axis to be projected onto and across a surface when the pathway light  10  is installed at an edge of the surface. 
       FIG. 3A  shows the pathway light  10  installed on a concrete sidewalk  70 . When the pathway light  10  is installed at the level of the sidewalk  70 , the light source housing  20  may be placed directly on the top surface  70   a  of the sidewalk  70 . As can be seen, the low profile of the pathway light  10  results in minimal protuberance of the housing above the top surface  70   a  of the sidewalk  70 . 
       FIG. 3B  shows the pathway light  10  installed on the concrete sidewalk  70  looking from a different angle. A bolt  80 , as shown, may be used to affix the pathway light  10  to a vertical surface or peripheral edge  70   b  of the sidewalk  70 . The bolt  80  may be pre-cast into the concrete or directly driven into the concrete. Alternatively, a plastic or metal anchor may be installed in the concrete to accept the bolt  80 . Similar installation methods may be used for installation onto wood, metal or bituminous pathways. 
       FIG. 4  is a schematic diagram of a controller  60  that may be used in a luminaire, such as the pathway light  10 , according to one non-limiting embodiment. Alternatively, buck type switch-mode current regulators or other controllers may be used in place of the controller  60 . The controller  60  receives alternating-current (AC) or direct-current (DC) power from a power source (not shown) at J 1 . In the case of AC voltage, the AC voltage of the received power is converted to direct-current (DC) voltage by D 1  and C 1 . In the case of DC voltage, D 1  passes the DC voltage in a polarity independent way so wiring polarity does not need to be observed. A voltage reference is provided by U 2  and stable over variations in ambient temperature and supply voltage, and sets a reference that is a set point for the current output to the light source of the pathway light  10 , represented by LED 1  in  FIG. 4 . The amplifier U 1  detects the difference between the current through LED 1  and the set point. If the current through LED 1  is less than the set point, U 1  increases the gate bias on transistor Q 1  to increase the current. Conversely, if the current through LED 1  is greater than the set point, the gate bias on Q 1  is decreased to decrease the current through LED 1 . Resistor R 1  is a sense resistor that measures the current flowing through LED 1  by converting the current to a voltage for input to U 1 . Resistors R 3  and R 4  form a voltage divider that divides the voltage reference from a standard 1.24 volt to a lower voltage so that a small value resistor may be used for resistor R 1 . Because the power dissipated by R 1  is I LED1   2 *R 1 , a smaller R 1  wastes less power and provides for a lower dropout voltage (loss of regulation) for the controller  60 . The use of a power field-effect transistor (FET) type of pass transistor for Q 1  enables a very low dropout voltage and low gate current consumption. Alternatively, a bipolar-junction transistor (BJT) would work in the controller  60  albeit with reduced performance. Resistor R 2  provides bias current for reference U 2 . The dual diode setup D 2  serves to protect against damaging power line transients. Fuse F 1  protects the rest of the circuit of controller  60  from short circuit or failure of the other electronic components, and from a power source voltage exceeding the limiting value of D 2 . Capacitors C 2  and C 3  are bypass capacitors that provide noise filtering and stability to the reference U 2  and amplifier U 1 . 
     The controller  60  permits full light output operation of the luminaire to within less than 1 volt of the minimum voltage needed to power the light source for emission of light because of the low dropout voltage of the controller  60 . If the supply voltage falls below the minimum level for full output, the controller  60  continues to allow the light source to emit some light, reducing in intensity as the voltage falls. In one embodiment, the luminaire uses standard 12 VAC power that is commonly used with traditional pathway lights (“low voltage lighting”). In one embodiment, two or more power wires enter the housing of the luminaire and are attached to the power source wires using “wire nuts”, insulation displacement connectors, soldering or other method. 
     An additional benefit provided by a luminaire employing the controller  60  is the substantial reduction in the consumption of power. This is because of the direct illumination of the pathway (or whatever surface is to be illuminated) and the use of a solid-state type of light source, such as the LED device  50 , coupled with the specially designed electronic control circuit, such as the controller  60 . Another benefit provided is the ability of the controller  60  to operate over voltages very close to the minimum voltage required by the solid-state light source, thus enabling the low voltage supply to be fully loaded (which causes a voltage drop), which in turn enables the use of smaller power sources versus traditional light sources. 
     The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Although specific embodiments and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. The teachings provided herein of the various embodiments can be applied to other contexts, not necessarily the exemplary context of pathway illumination generally described above. 
     For example, instead of using the standard 12 VAC power as the power source, in one embodiment the power source may be an alternative power source such as a battery, super- or ultra-capacitor, fuel cell, photo-voltaic cell, wind turbine, geothermal pump, etc. In another embodiment the power source may be any combination of the standard 12 VAC power and one of the aforementioned alternative energy sources, or any combination thereof. Of course, the controller  60  will be appropriately modified to adapt to the power source in order to provide regulated power to the light source. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.