Abstract:
A high-intensity LED lighting system is presented whereby one or more LED lighting fixtures are affixed to an elevating structure, the elevating structure having a substantially continuous internal pathway. Said pathway can be used as a conduit or duct for pressurized air which is introduced at or near the bottom of the elevating structure and forced upwardly toward the lighting fixtures so to provide cooling of one or more components of the lighting fixtures so to, ultimately, improve the efficacy of the LEDs contained therein. A method of designing lighting systems, including analysis of whether or not to add air cooling to increase light source efficiency is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to provisional U.S. application Ser. No. 61/645,870 filed May 11, 2012, herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     In the field of sports and wide-area lighting, manufacturers are attempting to find ways to make the use of light-emitting diodes (LEDs) competitive where high-intensity discharge (HID) lighting has traditionally been dominant. LEDs can be made more competitive by increasing their lumen output, improving efficacy (lumens per watt), increasing longevity, and reducing cost. Thus, any technology that has the potential to improve on one or more of these factors is desirable in the lighting industry. 
     Certain techniques for improving individual factors are well known in the industry; however, improving one factor may diminish other factors. For example, LEDs are typically rated for lumen output @ 25° C. and 350 mA. Increasing current increases lumen output, but lowers efficacy at the same temperature; still worse, when temperature increases as is typical with increased power input, efficacy and lumen output decrease. 
     Likewise, LEDs can have a much longer average life than other types of lighting (e.g., on the order of 50,000 hours versus 5,000 hours); however, average life is reduced significantly as the LEDs are operated at higher temperatures and currents. LED life can be reduced by one or two orders of magnitude by operating at higher currents and temperatures that are still considered to be within viable operating parameters (e.g., 1000 mA and 125° C.). This can reduce their usability for lighting applications requiring thousands of hours per year of ON time, but is not necessarily a liability for lower usage applications such as some types of sports lighting (which may require as little as 250 hours of ON time per year). 
     The cost for fixtures and support structures is a very significant part of LED lighting cost. Reducing the number of LEDs required per fixture to achieve a given light level on a target area can significantly lower overall costs; however, reduction of the number of LEDs requires increasing light output per LED, which results in reduced average life due to higher currents and operating temperatures. 
     Therefore, managing LED temperature is important to optimizing efficiency, efficacy, and cost. Thus, there is room for improvement in the art. 
     SUMMARY OF THE INVENTION 
     While the use of LEDs in wide-area or other lighting applications typically employing HID or other traditional light sources seems promising (e.g., due to the longevity of LEDs), one must consider an issue previously unaddressed (in many cases) for lighting systems using traditional light sources: heat management. 
     It is therefore a principle object, feature, advantage, or aspect of the present invention to improve over the state of the art and/or address problems, issues, or deficiencies in the art. 
     According to an aspect of the present invention, an elevating structure of a lighting system is utilized as a way to route pressurized air to high-intensity LED lighting fixtures elevated on that elevating structure. In one aspect, a continuous pathway that exists naturally in the interior of the elevating structure is taken advantage of as an air conduit or duct from a source of pressurized air traveling from well below the fixtures up to the fixtures. As one option, any mounting structures (such as cross arms), fixture mounting knuckles, and the like that have continuous internal pathways can also be taken advantage of by putting them in fluid communication with the pathway through the elevating structure. 
     Another aspect of the present invention relates to designing LED high-intensity lighting systems by determining the amount of and uniformity of illumination needed at a target area, determining potential placement of lighting fixtures relative the target area (including elevation and distance away), and determining a conventional set of LED lighting fixtures that will meet or exceed intensity and uniformity levels for the target area over a conventional or desired amount of normal operating life. Then, a determination will be made of whether or not the cost of an air cooling subsystem is justified. Some considerations include, but are not limited to, establishing a source of pressurized air mounted below the fixtures on an elevating structure, creating air pathways to the fixtures elevated on the structure, and capital and operating costs for such a subsystem over its normal operating life. In some instances, the elevating structure has original built-in continuous pathways that can be taken advantage of for airflow pathways from the pressurized source to the fixtures to eliminate the need for separate air conduits or ducts. A designer can evaluate capital costs and operation costs based on a certain airflow capacity relative to amount of additional efficacy of the fixtures for such air cooling, to determine such things as how much airflow capacity would be added, whether or not capital costs could be reduced by reducing the number of LEDs or even fixtures for a given application, and including in some instances whether entire elevating structures and fixtures could be eliminated by an increase in efficacy from air cooling. 
     One embodiment according to the present invention uses air cooling to reduce the temperature of wide-area lighting fixtures. A small blower or fan (e.g., on the order of ⅓ horsepower) is installed with its output directed into a hollow lighting support pole. Air distribution is through the pole and either coaxially through the fixture mounts, or through appropriate ducting from the pole to the fixtures. Air is directed through the fixtures or to the heat sink on the back side of fixtures. Power usage for the blower would be calculated and energy cost for the blower versus potential power savings for the fixtures compared, with optimum values calculated based on the needs of the project. For the example of model XP-G LEDs, available from Cree, Durham, N.C., USA, efficacy increases on the order of 10-15% should be achievable, resulting in cost savings of tens or hundreds of dollars. This method would ideally be applied to sports lighting applications, which typically have many high wattage fixtures mounted on each pole. This allows the cost of the blower and its energy draw to be allocated to many fixtures. Further, since increasing total light output per fixture is very beneficial for sports lighting, and since a major limiting factor in using LEDs in sports lighting is temperature rise due to increased power, significant cost savings might result. Conversely, for other wide-area lighting (e.g., parking lot lighting, street lighting, etc.), while the cost savings resulting from the increased energy efficiency attributed to air cooling might not in itself be enough to make air cooling economically advantageous, air cooling might increase expected LED life enough to make air cooling economically feasible as well. 
     These and other objects, features, advantages, or aspects of the present invention will become more apparent with reference to the accompanying specification and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       From time-to-time in this description reference will be taken to the drawings which are identified by figure number and are summarized below. 
         FIGS. 1 ,  2 ,  3 A and B illustrate a cooling system for lighting fixtures according to a first exemplary embodiment of the invention. 
         FIG. 4  illustrates an alternative exemplary embodiment according to aspects of the invention. 
         FIG. 5  illustrates a method for design and installation of LED lighting systems according to aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A. Background 
     As indicated above, the context of the invention relates to improvements in efficacy of high-intensity LED fixtures which are elevated for wide-area lighting; specifically, via air cooling of one or more components of the fixtures. It is to be understood that the following detailed description is to assist in a better understanding of the invention and its aspects. It is not intended to be exclusive or inclusive of all forms and embodiments the greater invention can take. 
     As envisioned, air cooling can reduce the operating temperature of LED fixtures down to near-ambient with a relatively simple apparatus. Such a cooling system may generally be described as including a small blower or fan, on the order of ⅓ horsepower, installed with its output directed into a hollow lighting support pole. Air distribution flows through the pole, through hollow cross arms, and through channels or pathways in the fixture mounts with the air being directed to the heat sink on the back side of the fixtures; the use of heat sinks to dissipate heat from LEDs is well known in the art. Power usage for the blower is calculated and the energy cost for the blower versus potential power savings for the fixtures compared, with optimum values calculated based on the needs of the project. Factors to consider when evaluating the benefit of such a system include, but are not limited to: 
     a. kW-hr cost of electricity; 
     b. efficacy versus temperature curve for LEDs; 
     c. cost for blower and controls; 
     d. costs for additional ducts and tubing, if required; 
     e. costs for air sealing any pole or fixture openings, if required; and/or 
     f. maintenance costs for blowing equipment. 
     Table 1 below illustrates test results from air cooling a 24-LED fixture of the type disclosed in U.S. published patent application 2010/0195326, now U.S. Pat. No. 8,449,144, incorporated by reference herein and commonly owned by the assignee of the present application. LEDs were model XP-G available from Cree, Durham, N.C., USA. The fixture was operated at near-constant power but, as can be seen, temperature declined with increased air speed. In these tests, air cooling was achieved by directing air at the approximate speeds indicated in Table 1 across the fixture. This air was generally enclosed and directed onto the heat sink (and not generally disbursed). Thus, it is believed that such airflow fairly uniformly impacted the entire fixture (as opposed to being simply focused on one localized part). As can be seen from Table 1, the percent lumen increase is not linear relative to air speed. This discovery can be beneficially used by designers in weighing the various and sometimes antagonistic factors between capital and operating costs of adding such a cooling system and light efficacy improvements or benefits for the lighting system. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Lumen 
               
               
                   
                 Power 
                 Temperature 
                 Air Speed 
                 Lumens 
                 Increase 
               
               
                 Test 
                 (W) 
                 (° C.) 
                 (mph) 
                 (lm) 
                 (%) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 222.5 
                 123 
                 0 
                 13640 
                 (base) 
               
               
                 2 
                 230.1 
                 87 
                 9.5 
                 15822 
                 16 
               
               
                 3 
                 238.6 
                 82 
                 18 
                 16170 
                 18.5 
               
               
                   
               
             
          
         
       
     
     B. Exemplary Method and Apparatus Embodiment 1 
     In a first embodiment, pole  15 ,  FIG. 1  elevates light fixtures  40  some distance in the air, on the order of (for example) 50 feet or more. One example of light fixtures  40  are model STR-LWY-15-HT available commercially from BetaLED, Sturtevant, Wis., USA. Another example of light fixtures  40  are those disclosed in U.S. patent application Ser. No. 12/626,095, incorporated by reference herein and commonly owned by the assignee of the present application. An example of pole  15  is model LSS50A available from Musco Sports Lighting, Oskaloosa, Iowa, USA, which is essentially a hollow galvanized steel tapered pole of either one piece or multiple slip-fit sections. Pole  15  presents a continuous air pathway from its bottom to top. A typical fifty foot tall pole of this nature has a largest outside diameter of approximately 10 inches at its bottom (approximately 79 square inches cross-sectional area), and approximately 6 inches smallest outside diameter at its top (approximately 28 inches square cross-sectional area). Whether one piece or several slip-fit sections, pole  15  is substantially air tight. It would represent an overall interior volume of approximately 27,000 cubic inches. There may be handles or other openings for the introduction of electrical wirings that could also occupy some of the interior volume of the pole. As mentioned, said openings can be substantially sealed off, or at least sealed or blocked enough that at a pressurization or airflow level selected, airflow would not be significantly diverted from being delivered up to the light fixtures for cooling. Pole  15  is hollow, but essentially sealed. With this particular pole, the bottom of the metal, tubular pole is slip-fit for several feet over a mating concrete stub to support the pole in a vertical position. Thus, several feet of the bottom of the pole would be occupied by that interference-fit concrete stub. Additionally, the top of such a pole would normally have a cap and/or could have what is called a pole top fitter. A pole top fitter could comprise a hollow tubular section to which cross arms and a top closing cap can be slip-fit, with the fitter slip-fit on the top tapered end of the main pole. In any case, introduction of pressurized air into the pole and routing up through the pole to a location at or near the fixtures would take into account such features. 
     Blower or fan  20  is installed on the pole, with the outlet of the blower directed into an opening  30  in pole  15 . As indicated in  FIGS. 1 ,  2 , and  4 , blower  20  could be mounted at or near pole  15  along its length such that its output is introduced into the hollow interior of pole  15 . In the illustrated examples, a separate mounting platform or structure  10 ,  FIG. 1  can first be attached by appropriate fastening devices along the pole at the appropriate location. Blower  20  would then be mounted or supported on that platform. An appropriate opening into pole  15  would be formed and the intersection of the blower and pole at least substantially sealed by any of a variety of appropriate means. Alternatively, blower  20  might have mounting hardware to mount it to pole  15 , or otherwise sufficiently be supported at its interface with pole  15  so to no longer require a separate platform. As can be appreciated by those skilled in the art, the type and operation of blower  20  can vary according to desire and need. Factors could include the amount of airflow and speed delivered to the fixtures suspended at or near the top of pole  15 . Factors could further include the internal volume defined by pole  15  and any subsequent conduits to fixtures  40 , the leakiness or lack thereof of air (caused by, for example, other items attached along the pole, pole joints, joints between such things as cross arms and fixture mounts, etc.), whether other components occupy the interior space of pole  15 , and the like. In this embodiment, one example of blower  20  is described below. Any other openings into pole  15  may be sealed, or may present a small enough air leak such that it does not matter to the desired cooling function. 
     As indicated in Table 1, the designer can select a blower output capacity by referring to a derived empirical relationship between air speed relative to percent lumen increase. For example, substantial leakiness in the air pathway from blower  20  to fixtures  40  may result in a substantial drop in air speed as measured at the fixtures. But, as indicated at Table 1, even a substantial drop between the two can result in a substantial percent lumen increase if enough air speed can be generated at the fixtures. As will be appreciated by those skilled in the art, the ultimate outlet of pressurized air at the fixtures will represent the least restrictive path for pressurized air. In other words, by known fluid dynamics, the designer can encourage the pressurized air from the output of the blower to move with the least airflow resistance to an outlet at the fixtures so to minimize losses or leakiness. As such, U.S. patent application Ser. Nos. 12/626,095 and 12/623,875, now U.S. Pat. No. 8,651,704, both of which are incorporated by reference herein and commonly owned by the assignee of the present application, may be referenced for details regarding how airflow from a pressurized air source can be effectively directed to an LED or solid-state light source fixture for effecting cooling during operation. U.S. patent application Ser. Nos. 12/626,095 and 12/623,875, now U.S. Pat. No. 8,651,704, provide a variety of different embodiments; some direct air from an airflow pathway directly onto the LED fixture heat sink. Others are directed into a housing around the heat sink. The aforementioned references are intended to provide several examples of a feature the figures and description herein illustrate; namely, that the elevating structure itself can originally and naturally have a continuous internal pathway which can be used for or converted into an air duct from a pressurized air source such as blower  20  up through the elevating structure to the fixtures of a lighting system. Airflow from the blower travels up through the pole and escapes out opening  50  and is directed by tubes  80  to individual fixtures  40  (see  FIG. 3B ). As can be appreciated, tubes  80  can be of any number of materials and configurations. Ideal examples would be materials that could withstand outdoor environmental conditions for decades (e.g., 24 gauge galvanized pipe). Other examples might include a number of UV-stable thermal plastics. Another suitable material could comprise a metal flexible hose such as available from Air Handling Systems, Woodbridge, Conn., USA; such tubing has some flexibility to allow for thermal expansion and contraction and some relative movement between fixtures and their cross arm  60  or pole  15 . The terminal outlet end of said tubing could have a fitting (e.g., such as also available from Air Handling Systems) or could simply have an open end. Air could be simply outlet from that open end or there could be some sort of distribution fitting like a manifold also available from Air Handling Systems, Woodbridge, Conn. Openings  30  and  50  (see  FIGS. 2 and 3B , respectively) may be tightly sealed to the blower and air ducts, or may allow for some air leakage as long as air flow is sufficient to provide cooling to the fixtures. 
     According to the present embodiment, air flow may be directed to the heat sinks of LED lights contained in fixtures  40 , or to the bases or envelopes of other types of lighting elements that may be contained in fixtures  40 . Alternatively, air may be directed into cross arm  60 , and through mounting knuckles  70  (see  FIG. 3A ). From there air may be directed to LED heat sinks or bases or envelopes of other types of lighting elements. In this embodiment, cross arms  60  have a 6 foot span, a tubular interior constant cross-sectional area of approximately 6 square inches, and a volume of approximately 4400 cubic inches, and are available from Musco Sports Lighting. Mounting knuckles  70  could be like those described in published U.S. patent application 2011/0149582, incorporated by reference herein and commonly owned by the assignee of the present application. Such knuckles are intentionally made to mount underneath cross arm  60  where there would be an opening into a first half of knuckle  70  with an air path that would extend to a second half attached to a fixture  40 . An air path would extend all the way through knuckle  70  even though there is a pivotable joint between the two halves. An opening into the back of fixture  40  would then provide a complete air pathway from cross arm  60  to the interior of fixture  40 . Air could then leave through ventilation openings in  40  such that airflow would be encouraged from blower  20  through the hollow interior of pole  15 , the hollow interior of cross arm  60 , through knuckle  70 , and into each fixture  40 , at an air speed and volume per unit time to effectuate a percent lumen increase on the level desired or needed for a given design. Of course the designer would likely take into account how many fixtures were installed on each pole  15  (in this example, there could be many or just a few) when calculating a necessary air speed and volume. 
     A blower that could be used to provide airflow is the Peerless ⅓ HP Pressure Blower PW-8, which operates at 3500 RPM and delivers 256 CFM at 1 inch static pressure, available from Global Equipment Company, Port Washington, N.Y., USA. But as previously mentioned, the type and output of the component which produces the pressurized air source or airflow can vary according to need and desire. Ideally, the component would be suitable for use in outside environments for decades. Said component could utilize the same electric power source that is used to power the light fixtures. Optionally, the blower could be enclosed by some covering or housing. 
       FIG. 2  illustrates a larger view of the blower installation. As can be appreciated, blower  20  can have its own mount or no mount (and just rely upon some mounting interface to the side of pole  15 ). Alternatively, blower  20  might be mounted on other pole-mounted components. For example, it might be mounted on top of an electrical enclosure box  35 ,  FIG. 1  above ground level but well below fixture level, as are conventional on many light poles.  FIGS. 3A-B  illustrate a larger view of the components at the top of the pole.  FIG. 3B  shows supply of airflow via tubes  80  directly from pole  15 .  FIG. 3A  shows in dashed line arrows the flow path from pole  15  into the interior of cross arm  60  and then through a continuous air pathway through mounting knuckles  70  to fixtures  40 . As can be appreciated, there could be more fixed or rigid air conduits instead of hoses or instead of using the existing structure of pole, cross arm, and knuckles. For example, there could be rigid metal air ducts from pole  15  or cross arm  60  to fixture  40 . However, in the embodiments in  FIGS. 3A and 3B , the routing of air via tubes  80  or directly through the mounting structures allows freedom of adjustment of fixtures  40  relative cross arm  60  without requiring customized conduits for airflow. 
     C. Exemplary Method and Apparatus Embodiment 2 
       FIG. 4  illustrates a second embodiment having a pole  15 , blower  20 , opening  30 , and LED fixture with heat sink  90 . Arrows  25  indicate airflow through the pole and fixture. As is illustrated in  FIG. 4 , airflow through pole  15 , and then across a mounting interface  45  (e.g., as may be appropriate for a non-adjustable or static mounting situation), can provide a direct, continuous air path to the inside of a fixture and the proximate edge of heat sink  90 . That air can be directed through and across heat sink  90  and out some type of vent at the distal edge of heat sink  90  so to provide an exhaust for the airflow. U.S. patent application Ser. Nos. 12/626,095 and 12/623,875, now U.S. Pat. No. 8,651,704, provide some examples of airflow paths. 
     D. Options &amp; Alternatives 
     As can be appreciated, the foregoing detailed description gives but a few examples of apparatus and methods according to the present invention. Variations obvious to those skilled in the art will be included within the invention. 
     It will also be appreciated that the discoveries of the inventor also engender methodologies that can be useful for design and installation of LED lighting systems. 
     One method may generally be described according to process  1000  illustrated in  FIG. 5 . As indicated above, a method can include as a first step (reference no.  1010 ), deriving by methods known in the art a desired or required light level and uniformity for a target area. As a second step (reference no.  1020 ), the designer can then utilize computer programs (reference no.  1040 ) such as are routinely used in the industry and by manufacturers, or empirical testing (reference no.  1030 ) of LED fixtures that are candidates for the installation, to determine a baseline light output when a fixture is operated normally without any auxiliary air cooling. Then it can be determined, via empirical testing (reference no.  1050 ), how such candidate fixtures would react to air cooling during operation (e.g., as in Table 1). Having these data, a comparison (reference no.  1060 ) of estimated (or measured) percent lumen increase at a given power level (i.e., efficacy increase) can be made to the capital cost and operating cost of candidate air cooling systems. The designer, either alone or with an end user or customer, can then determine (reference no.  1070 ) whether a given candidate air cooling sub-system should be added. Some variables that may affect whether or not to add a cooling sub-system include, but are not limited to: different airflow volume and speed at the fixtures, where/how many air pathways exist, cost of electrical power to operate the LEDs and the air cooling system, whether or not the LEDs would be overdriven or under-driven relative to recommended or rated operating wattage by the manufacturer of the LEDs, and whether or not the number of LED fixtures can be reduced for an installation (which could reduce capital and operating costs) and/or eliminating a whole pole or elevating structure with a number of fixtures because of the cumulative increase in light output from other poles and fixture arrays with the cooling system.