LED venue lighting system with first and second housing having an air passage therebetween

An outdoor area LED lighting system including: a housing containing a large array of LEDs mounted to an aluminum direct thermal path printed circuit board and a single lens. The large array of LEDs are capable of producing light rays directed through the single lens to produce a beam of light to illuminate the outdoor area. The single lens is preferably a Fresnel lens. The housing is preferably capable of being sealed in a weather-tight manner. A second housing may at least partially surround the first housing such that at least one air passage is provided between the first housing and the second housing. A heat sink including a heat block in thermal communication with a plurality of heat tubes and fin assemblies may be in partial thermal contact with the LED module and in fluid communication with the at least one air passage. At least one fan may be provided in or in fluid communication with said at least one air passage to cool the heat sink. A digital interface may connect the LED module to a host computer to monitor and track information and trending for statistical process control.

FIELD OF THE INVENTION

The present invention relates to LED based light fixtures. More particularly, but not by way of limitation, the present invention relates to a venue lighting system for arenas and stadiums employing light emitting diodes.

BACKGROUND OF THE INVENTION

The demands of venue lighting are unique. For example, NFL stadiums generally light the field with a minimum of 250 foot candles at any point on the playing surface. To achieve this level of illumination with metal halide lamps requires roughly one megawatt of electrical power for the field alone. While metal halide lamps are presently the standard, they are not without drawbacks.

One concern with metal halide (also known as high intensity discharge, or HID) lamps is bulb life. While lower wattage bulbs may exhibit as high as 20,000 hour bulb life, higher power bulbs, such as the 1,500 watt bulbs commonly found in stadium fixtures, typically have bulb life expectancy in 3,000 hour range. A number of other concerns are related to bulb life, such as: envelope failure (bulb explosion) occasionally occurs towards the end of life or during bulb changes; lumen maintenance (brightness fall-off); cycling where the bulb turns off and on, seemingly at will; etc. While envelope failure is not common, it is of major concern since the envelope is made of glass and fixtures must enclose the bulb in such a way that flying glass cannot escape. Regardless, bulb failures in a fixture mounted on a tower high above a stadium are expensive and unwanted. To avoid catastrophic failures, many metal halide bulb manufacturers recommend group re-tamping at the end of the stated life, rather than spot changing individual bulbs.

Another concern is start-up and hot restrike. In a conventional probe-type metal halide bulb, ignition of a cold bulb involves igniting a small starter arc which brings the gasses in the bulb up to pressure and heats the gasses so that they are more easily ionized to start the main arc. This process typically take five to seven minutes, during this time the bulb produces significantly less light and the color temperature fluctuates significantly. Newer pulse start bulbs eliminate the probe and warm up times are reduced, but warm up can still take on the order of two to four minutes. While 1,500 watt pulse start bulbs and ballasts are available, they have not been widely accepted for field lighting, generally speaking, pulse start technology has found favor in lower wattages.

Hot restrike is of greater concern than initial start-up. Probe-type bulbs in the wattage range used for field lighting will not restart when the gasses in the bulb are hot. The hot restrike process can take up to 20 minutes. This problem was brought to the world's attention during the Superbowl in February 2013 when a momentary loss of power resulted in a 45 minute blackout during the game. Pulse start bulbs similarly reduce hot restrike times but the time delay required to reignite a bulb are still measured in minutes. Instant restrike ballasts are available for pulse start bulbs, but voltages on the order of 30,000 to 40,000 volts are required to restrike a hot 1,500 watt bulb. These voltages limit the distance between the bulb and the ballast and require special wiring with very high dielectric strength insulation to avoid arcing outside the bulb during a hot restrike.

Another concern in using metal halide bulbs is video production. Obviously video production of sporting events is a concern at the professional and college level, but video streaming has brought these concerns to even the high school level. While the broad spectrum nature of metal halide bulbs is generally good for video production, the light is not optimum for televising sports. For example, all metal halide bulbs are driven with alternating current. This means the arc reverses at twice the operating frequency. In the United States, a metal halide bulb, with a magnetic ballast, will flicker at 120 Hertz. If high frame rates are employed for slow motion, this flicker will be obvious in the final video. While high frequency electronic ballasts reduce the effect, it still exists.

Another issue for video production is the color rendering index (“CRI”) of the light. A simplistic definition of CRI is the percentage deviation between a light source and sunlight, but the effect is the ability of the light source to render colors. Skin tones are especially problematic for low CRI light sources. The metal halide bulbs used in sports complex lighting typically have a CRI of about 65. While the light produced by such bulbs usually appears very white, the light typically has a surplus of energy in the 500 nm range of the spectrum, or a green spike. A green spike, coupled with green light bounce off the field, is typically handled by “white balancing” the cameras, but is still less than ideal for professional video production.

Yet another concern with metal halide bulbs is the production of ultraviolet light (UV). These bulbs produce significant amounts of short wave UV which can be dangerous to humans. Most bulbs include a borosilicate or fused silicate outer envelope which will absorb the vast majority of the short wave UV light. If the outer envelope is broken, most metal halide bulbs will continue to function but will emit dangerous amounts of UV light. So called “flash burns” or sunburn of the eye is a real danger to people in proximity to such bulbs. Even with the outer envelope in place such bulbs emit enough UV light to be damaging to plastics and can cause some finishes to fade over time.

Finally, there are environmental concerns with the disposal of such bulbs, in particular due to the use of mercury. While manufacturers have found ways to reduce the amount of mercury used in metal halide bulbs, some mercury is required to produce white light. Since the bulb envelope is glass, breakage after disposal is likely and thus the release of mercury is likely.

Light emitting diodes (LEDs) offer improvements over metal halide bulbs in all of these areas. However, light emitting diodes are not without their own challenges. Perhaps the biggest challenge to producing an LED luminaire for venue lighting is thermal management. A metal halide bulb radiates close to 85% of the input power as visible light, ultraviolet light and infrared energy, leaving 15% of the power which must be dissipated into the environment through conduction. In contrast, an LED radiates virtually no ultraviolet light and virtually no infrared energy, thus at least 55% of the input power must be dealt with through conduction. This is particularly problematic with large arrays of lights where hot air from lower fixtures in the array effectively raises the ambient temperature around higher fixtures.

LEDs are finding their way into indoor venue lighting. Such lights offer the advantage of instant on, whether hot or cold, and are even full range dimmable, unlike their metal halide counterparts. Indoor fixtures, of course, do not have to accommodate a wide range of ambient temperatures. Indoor venues can easily employ larger numbers of lower power fixtures, which can be located directly above the playing surface. Further, indoor fixtures do not have to compete with daytime light levels.

Some attempts have been made at lighting outdoor venues with LED fixtures. To date, such fixtures have been very large compared to metal halide fixtures or produce far less light for a comparable form factor. This would be particularly problematic in retrofitting towers in existing venues which have metal halide fixtures. Regardless, in both indoor and outdoor attempts, these fixtures have employed one lens for each LED or module, all employ multiple lenses. All of these lights will exhibit an inverse square fall off the light when the light strikes the playing surface at an angle and not straight-on. Typically these lenses have a relatively short focal length making it difficult to manufacture a fixture with consistent focus from LED-to-LED. The result is a bright hot-spot in the middle of the beam. Thus, to achieve very even lighting of the field is very difficult, at best.

Finally, neither metal halide lamps nor existing LED fixtures are particularly dark sky friendly. A movement has been afoot for several years to reduce unwanted light spillage into the night sky, or “light pollution.” Many outdoor metal halide fixtures include an “eyebrow” or visor to reduce the amount of upward spillage. This is only marginally effective. Metal halide bulbs emit light spherically. Only a small portion of the produced light is emitted toward the field. Fixtures typically use an aluminum reflector to capture some of the light headed rearward and reflect and focus it toward the field. A little more than one-third of the light produced by the bulb actually makes it to the intended target. Even with the visor, a significant portion finds its way skyward.

Individual LEDs are typically packaged to emit nearly all of the produced light in a forward direction. The types of LEDs currently employed in venue lighting typically emit light in a 120 degree beam. Most known fixtures use multiple small molded lenses, often called TIR lenses, to capture virtually all of this light and focus it into a narrower beam. Unfortunately, these fixtures also then employ a second clear lens to protect the LEDs and molded lenses from the elements. Some of the light striking this lens is reflected rearward into the fixture and later reflected back out of the fixture in random directions, including skyward.

Many outdoor architectural light fixtures, as well as other large outdoor area lighting fixtures, suffer from these same problems. In particular, inverse square fall off and dark sky issues are problematic in metal halide fixtures used to wash building walls, in fixtures used for airport tarmac lighting, etc.

Thus there is a need for a high power stadium outdoor light fixture which will minimize lamp replacements, is not constrained by a restrike interval, provide video friendly light, minimizes emissions outside the visible light range, provides effective thermal management, will not fail explosively, and minimizes skyward light emissions.

SUMMARY OF THE INVENTION

The present invention provides an LED based light fixture for venue lighting which overcomes the problems discussed above.

In one preferred embodiment an LED fixture is provided which includes a weather-tight housing, a high power LED array housed within the housing, a Fresnel lens covering the forward end of the housing, and a heat sink in thermal communication with the array for dissipating the heat produced by the module into the environment.

In another preferred embodiment, the inventive LED fixture further includes a fan for moving air over the heat sink to increase the rate at which heat is dissipated from the heat sink. Optionally, duct work may be used to discharge the heated air outside an enclosed venue during warm weather or duct the air to field level or to spectators during cold weather.

In a particular preferred embodiment, the LED fixture includes a two-part structure. One part of the two part structure includes the weather-tight housing enclosing the LED array, Fresnel lens and in some embodiments the heat sink. The second part of the two-part housing is not weather-tight and generally includes the power dissipating portion of the heat sink, the fan for moving air and air passages formed between the housings to allow the air to dissipate heat from the heat sink.

Another preferred embodiment includes an outdoor area LED lighting system including: a housing containing a large array of LEDs mounted to an aluminum direct thermal path printed circuit board and a single lens. The large array of LEDs are capable of producing light rays directed through the single lens to produce a beam of light to illuminate the outdoor area. The single lens is preferably a Fresnel lens. The housing is preferably capable of being sealed in a weather-tight manner. A second housing may at least partially surround the first housing such that at least one air passage is provided between the first housing and the second housing. A heat sink including a heat block in thermal communication with a plurality of heat tubes and fin assemblies may be in partial thermal contact with the LED module and in fluid communication with the at least one air passage. At least one fan may be provided in or in fluid communication with said at least one air passage to cool the heat sink.

In yet another preferred embodiment the heat sink is liquid cooled and the liquid is pumped to a location remote from the fixture for dissipating the heat into the environment. As used herein, unless otherwise stated, the term liquid and liquid cooled shall include any liquid known for cooling and heat transfer, including without limitation, water, antifreeze, a mixture, or other suitable liquids.

In still another preferred embodiment the LED array accommodates an input power of at least 1,000 watts and the LEDs are mounted on an aluminum substrate circuit board.

In still another preferred embodiment the inventive LED fixture provides an asymmetric array of LEDs and projects the light from the array through a single lens thus producing a beam of light having a predetermined gradient of light across the beam. The light is thus shaped to overcome the inverse square fall off of light associated with the light striking its target at an angle.

Further objects, features, and advantages of the present invention will be apparent to those killed in the art upon examining the accompanying drawings and upon reading the following description of the preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the construction illustrated and the steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation.

Referring now to the drawings, wherein like reference numerals indicate the same parts throughout the several views, one preferred embodiment of a light emitting diode based venue light102is shown in its general environment inFIG. 1. As is well known in the art, to light a playing field requires a number of fixtures102(24shown) usually mounted on a tower, pole104, or stand. The precise number of lights depends on desired light levels, driven mainly by the level of play. By way of example, 25 foot candles of light delivered to the field may be acceptable for outdoor sports at the municipal or high school level, 150 foot candles is generally acceptable for nationally broadcast college games, and 250 foot candles for professional football stadiums. While the safety of the players and spectators is a consideration, the needs of television broadcasters are a major consideration in determining lighting levels at college and professional venues. Typically fixtures102are mounted to pole104by way of cross arms106, or perhaps one or more trusses. In some cases, catwalks may be located proximate each cross arm106to facilitate aiming and maintenance of fixtures102.

For purposes of the present invention, the terms “fixture,” “luminaire,” and “head” are used interchangeably to refer to a single lighting instrument, such as fixture102. Turning toFIG. 2, in one preferred embodiment fixture102comprises: a housing202; a lens204at a forward end of housing202, wherein lens204is preferably a plastic Fresnel lens attached to housing202in a weather-tight manner; a forward bezel206for receiving lens204and visor208; ring210which allows entry of cooling air; aft (or second) cover assembly212; and yoke214pivotally attached to aft (or second) housing212.

With reference toFIG. 3, preferably lens204is a Fresnel lens, preferably formed of a transparent plastic, such as acrylic or polycarbonate. In one preferred embodiment lens204includes a flange302including a plurality of holes304(12shown) for securing to the housing with screws and a refractive area306.

Turning next toFIGS. 4 and 5, wherein the interior details of luminaire102are shown, luminaire102further comprises a first housing440which may be a reflector414received inside of second housing202to create airway420. Reflector414has a forward opening over which lens204is mounted using screws416. A ring-like gasket418is received between lens204and reflector414to protect the interior of fixture102from inclement weather in a weather-tight manner. As used herein, the term weather-tight or weather-tight manner does not, necessarily, require an air-tight submersible seal but instead capable of sealing against rain, blown dust and debris and the like. Towards the back end of reflector414light emitting diode module402is mounted to heat sink406such that light emitted from module402is directed towards lens204. In one preferred embodiment, LED402is a chip-on-board, or COB, type module. One such module is a VERO 29 LED module manufactured by Bridgelux, Inc. of Livermore, Calif. Such modules are well known in the art. COB modules typically emit light over about a 120 degree beam. To maximize the light harnessed from LED module402, condensing lens404may be used to collect and direct the light towards Fresnel lens204.

Heat sink406includes heat block422which provides a mounting surface for module402and receives a plurality of heat tubes408. Heat tubes408conduct heat produced by module402to fin assemblies410which are located in airway420distributed about the periphery of reflector414. It is a feature of the fixture102of the present disclosure to include a two-part housing. The first part housing440of the two-part housing includes LED module402, lens404, reflector414(which may form a segment of first part housing440), and Fresnel lens204all sealed by gasket418compressed by screws416. In certain embodiments, the heat block406may be at least partially within first part housing440. It shall be understood by one skilled in the art that first part housing440may be sealed in a variety of suitable ways, including adhesive, mating threads between reflector414and flange302(or Fresnel lens204), interlocking tabs, rivets, or the like. A second part housing450includes outer housing202, typically heat block406, heat tubes408, fin assemblies410and fan assembly412. An airway or air passage420is formed between first part housing440and second part housing450. Fan412draws air into airways420, through fin assemblies410, and discharges the heated air out the back of fixture420, thus providing cooling of fixture102.

The geometry of first part housing440and second part housing450may be varied as desired or required for design and/or application purposes. For example, and without limitation, first part housing440and second part housing450may be conical or frusto-conical as depicted inFIGS. 4, 4A and 4Bor may be cylindrical as depicted inFIG. 2. Alternatively, one skilled in the art would recognize that other geometries are contemplated, such as, without limitation, pyramidal, triangular, squared, oval, etc. Additionally, first part housing440and second part housing450could be different geometries from each other provided air passage420is included to allow the flow of air between first part housing440and second part housing450produced by fan412so as to cool heat sink406.

In one alternate embodiment, fan412may be reversible so as to reverse the flow of air within airways420. The purpose of this is to be able to clear any type of clog that may have formed such as storm debris, bird nests, water, or even ice which may form in the winter.

With reference toFIGS. 4A and 4Bin an alternate preferred embodiment, a shutter424may be inserted in the interior of reflector414. Shutter424may be beneficial in any embodiment but may have particular utility when fixture102is employed for architectural applications, particularly when directed toward the sky and where lens204may receive direct sunlight.

Shutter424is preferably coated on one surface426with reflective material similar to that coating the surfaces of the interior of reflector414such that when shutter424is in the open position, as depicted inFIG. 4A, surface426reflects and directs light out of reflector414through lens204in the same manner as inFIG. 4. Alternatively, shutter424may be closed as depicted inFIG. 4Bso as to protect LED402from potential damage from sunlight entering the interior430of reflector414which may be otherwise focused by lens204on LED module402. Surface425of shutter424may be coated with a reflective material to reflect such light and/or heat or may be optionally coated with a light and/or heat absorptive materially as a design preference.

In the embodiment depicted inFIGS. 4A and 4B, shutter424pivots from a hinge432and may extend across the interior430of reflector414at an angle when closed. Shutter424is thus positioned to be out of the focal point of lens204so as to avoid concentration of sun rays/heat on shutter424. As will be apparent to one of skill in the art, shutter424could be designed to have a geometry which matches the geometry of the interior430of reflector414or any other suitable fashion and position to accomplish the task of protecting LED module402.

In a preferred arrangement, shutter424would be closed (FIG. 4B) in the resting/off state of fixture102. A motor or solenoid434may operate to open shutter424(FIG. 4A) such as when LED module204is activated (turned on) and close when LED module204is deactivated (turned off). Further, fixture102may be designed such that motor434could maintain shutter424in the closed position (FIG. 4B) in the event LED module204fails to light or goes out due to malfunction or overheating. Alternatively, fixture102may be designed such that LED module204remains deactivated (turned off) in the event shutter424fails to activate (open).

In an alternate embodiment, shutter424could be configured as an aperture such as a diaphragm shutter found in a camera lens, for example. Preferably, shutter424is positioned within the sealed first part housing440within the interior430of reflector414but could alternatively be positioned outside or on top of lens204such as in a basic embodiment. Shutter424could even be a leaf shutter manually positioned between an open and closed position.

With reference toFIG. 6, duct602may be used to deliver heated air from fixture102remotely. In an enclosed stadium, duct work could be used to exhaust the heated air outside when the weather is warm, thereby reducing the air conditioning requirements for the complex, or be ducted to field or seating level in cold weather to augment heating equipment. For example, if a football field is lighted to achieve 250 foot candles at field level, over 1.2 million Btu/hr of heat could be delivered outside, reducing the air conditioning requirements by approximately 100 tons. To further improve performance, outside air could likewise be brought in for cooling the fixtures so that inside air would not be discharged outside.

With outdoor stadiums, air carried by duct602could be collected from large groups of lights and delivered to the sidelines to warm player benches in cold weather. In warm weather, the heated air would simply be discharged upwards and away from spectators.

In another preferred embodiment, rather than using a COB module, the LED module of the inventive luminaire employs a large, dense array of surface mount light emitting diodes700as shown inFIG. 7. Preferably, array700includes a plurality of LEDs702(1188shown) mounted on an aluminum substrate circuit board716, such boards are known in the art and available from several vendors. Preferably, the aluminum board would be a “direct thermal path” printed circuit board as manufactured by Sinkpad LLC of Placentia, Calif. One suitable LED is part number GS-3030W6-1G110-NWN manufactured by Shenzhen Guangmai Electronics Co., Ltd. Another suitable LED for this purpose is Cree XLamp LEDs manufactured by Cree, Inc., Durham, N.C. With further reference toFIG. 8, by way of example and not limitation, the LEDs702of board700are grouped in to 99 series strings802, each string having 12 LEDs.

It should be noted that in this embodiment, board700is laid out such that the number of LEDs contributing light are far fewer at the top720than at bottom722. Since the light is inverted as it passes through the Fresnel lens, when the fixture is pointed at the field, there will be more LEDs contributing light incident at the furthest point than at closer points, thus overcoming the inverse square falloff of light intensity typical of prior art fixtures.

Since the fixtures102are typically mounted as depicted inFIG. 1, the emitted light is not directly overhead of the field but rather strikes the field at an angle. The light intensity will not be the same across the beam (Keystone effect). The array ofFIG. 7accommodates for this and evens out the projected light intensity over the coverage area of the fixture. As stated above, this delineated, asymmetrical LED array straightens out the keystone effect. In such an embodiment it may also be desirable to include a heat sink which is asymmetrical as well to match the asymmetrical LED array700. Ideally, each LED702would operate at the same, or close to the same, temperature.

In an alternate arrangement, the array may use LEDs of different wattages so as to provide increased intensity areas. This may eliminate perceived dark areas or shadows as may be necessary or desired.

Additionally and/or alternatively, LEDs702may be grouped together in a plurality of separate electrical channels. This provides benefits in redundancy and other benefits. For example, without limitation, the different channels may be independently dimmed. A preferred arrangement would include at least two dimming channels. The preferred arrangement would include one driver for each channel and would each independently operate as discussed below with regard toFIG. 9andFIG. 10.

It should be understood by one of skill in the art that the asymmetrical design ofFIG. 7is one suitable embodiment, and that other suitable asymmetrical designs are contemplated. Such asymmetrical designs may be determined empirically as a result of the characteristics of the Fresnel lens selected as well as the geometry of the field or surface being lit by the fixture. As a result, alternate embodiments may be derived for certain conditions or to accomplish certain goals such as, without limitation, providing even lighting to the field or surface in the avoidance of dark areas or shadows.

FIG. 7Bdepicts an alternate array730. Array730includes a plurality of LED lighting elements732mounted to a board734. As shown, array730is an alternative embodiment symmetrical array disposed on a substantially circular board734. As is the case with the array depicted inFIG. 7, the array730ofFIG. 7Bmay include individual LEDs732of various wattage intensities. In addition, array732may be divided into a plurality of electrical channels such that each channel may be controlled/dimmed independently in the same manner as described above.

Turning toFIG. 11, the heat sink1100adapted for board700ofFIG. 7includes: a heat block1102a plurality of heat tubes1104pressed into block1102and a fin assembly1106coupled to the distal end of each heat tube1104. Each fin assembly1106comprises a plurality of fins1108pressed onto tube1104. Alternatively, board700may be liquid cooled using the liquid block1200ofFIG. 12. Liquid block1200includes passageway1206having a threaded inlet1202and threaded outlet1204such that fittings may be threaded into each end of passageway1206. Threaded holes1208are provided to attach a cover (not shown) with screws. Board700ofFIG. 7is attached to liquid block1200and a continuous flow of liquid is provided to cool board700. The liquid may be cooled elsewhere through a common heat exchanger. The advantage of such a system is the ability to remove large quantities of heat with small plumbing (as compared to ducting air).

As is well known in the art, parallel arrangements of LEDs do not load share well without ballasting. While variations in forward voltage can cause a single string to draw too much current, a larger problem is that the forward voltage falls as an LED warms up. Thus, if one string is warmer than its companion strings, the forward voltage of the string will fall causing it to draw more current at the expense of current flowing through the other strings. More current will cause the string to get hotter still causing the forward voltage to drop even more, and so the process continues. Ballasting radically reduces the positive-feedback between current hogging and thermal runaway. Thus each string includes a ballast resistor704. This arrangement is shown schematically inFIG. 8By way of example and not limitation, in the present embodiment a 2 ohm resistor is employed to control thermal runaway satisfactorily.

To illuminate the LEDs702, positive electrical power is applied at terminal710and negative power at712. In a preferred embodiment, the power applied at terminals710and712will be current controlled and deliver approximately 23 amps at maximum brightness. LEDs702are rated at one watt per device. While the LEDs702of board700are thus capable of operating collectively at 1188 watts, in the preferred embodiment it is contemplated that board700will be operated at 1000 watts, thus operating each string802at roughly 234 milliamps.

As stated previously, the proper method for driving LEDs is through current, rather than voltage, control. One scheme for properly driving the array ofFIG. 8is depicted inFIG. 9. Circuit900includes: terminal902for providing a voltage output; terminal904which provides a return path for the current flowing through terminal902; a transistor906for controlling the current received at terminal904; a current sense resistor908for developing a voltage proportional to the electrical current flowing through transistor906; a first amplifier910for scaling the voltage sensed across resistor908; and a second amplifier912for comparing the scaled current sense value to a reference voltage applied at input914. As will be apparent to one of ordinary skill in the art, transistor906is shown as a MOSFET, however, as will be apparent to one of skill in the art, a bipolar transistor could be substituted with only minor modifications.

When a current is flowing through transistor906a voltage is developed across resistor908. In one preferred embodiment, resistor916and resistor918are selected to provide a gain of ten. Thus, by way of example and not limitation, if 20 amps of electrical current is flowing through resistor908, the output of amplifier910would be four volts. If the voltage at input914is less than four volts, the output of amplifier912will move towards its minus rail, thus reducing the current flowing through transistor906. If the voltage at input914is greater than four volts, the output of amplifier912will move towards its positive rail, thus increasing the current flowing through transistor906. Accordingly, with an input of four volts, circuit900will regulate the LED current at 20 amps. It should be noted that amplifier912could be used as a straight comparator, but by reducing the gain to 100 with resistors920and922, the propensity of the circuit to oscillate or ring can be reduced. Optionally, capacitor924can be used to filter the output of amplifier912and thus limit the slew rate of its output to reduce overshoot and noise.

Another circuit which could be used to control the current through the LED array is shown inFIG. 10. Circuit1000is a switch mode buck current regulator, which are well known in the art. Circuit1000typically includes: an input1002for receiving an input voltage, a pass transistor1018for controlling the input current in a binary minor; a Schottky, or other fast recovery diode1020, to provide the current path when transistor1018is switched off; inductor1022; capacitor1024; terminal1006for providing an output current to the LED array; terminal1008for providing a return path; current sense resistor1010which develops a voltage proportional to the current through the LED array; amplifier1012which scales the voltage from current sense resistor1010; and controller circuit1004which compares the voltage from amplifier1012to a reference voltage and controls the duty cycle applied to transistor1018to maintain the desired current. By way of example and not limitation, if controller1004has a reference voltage of 2.4 volts, then amplifier1012may have a gain of six, as determined by resistors1014and1016so that 20 amps would produce 2.4 volts at the output of amplifier1012. Preferably controller1004includes a boost circuit including bootstrap diode1026and capacitor1028so that the output to the gate transistor1018will be higher than the voltage at input1002, thus allowing for the use of an N-channel device1018.

As will be apparent to one skilled in the art, the choice of using a linear circuit such as circuit900ofFIG. 9or a switch mode regulator such as circuit1000ofFIG. 10involves the balancing of a number of factors. At full brightness, by judicious selection of the input voltage, the efficiencies of the two circuits are comparable. During diming, the switch mode circuit will have better efficiency than the linear circuit. However, the linear circuit is far less expensive, far lighter weight, and does not raise the electrical emission concerns posed by the switch mode system.

As will be apparent to one skilled in the art, the present invention can incorporate an asymmetric array of LEDs to compensate for the inverse square fall off nature of light. This particular problem arises when a light source is aimed such that the light beams strike the target at an angle rather than straight-on. It should be noted that by passing the light generated by the light emitting diodes through a single lens, the asymmetric nature of the light can be preserved at the target location of the fixture. To achieve a like result from an array of LEDs which were individually lensed would require the array to employ many different lenses to provide varying beam sizes to achieve even lighting over the lit area.

The precise number of fixtures required for a particular venue will depend on a number of factors beyond just light levels. For example, the set back of the poles104(FIG. 1) from the field and the height of the lighting poles, the size of the area to be lit, how much light to put on spectator seating, sidelines, etc., the cost of the installation, the cost of operation, and the cost of maintenance are all considerations in a lighting plan. In the retrofit of metal halide lighting in an existing stadium, it is contemplated that the same number of fixtures could be employed following the original lighting plan for the facility. The fixtures would simply be dimmed to produce the desired light level. It would be apparent to one of skill in the art that dimming the fixture and the ability to dim (customize) for a particular event would maximize the efficiency of the fixture and thereby provide cost savings. In other words the fixture can be dimmed so that only the necessary amount of light is produced for the event, thus saving energy and money.

It should also be noted that the present invention is driven by DC electrical power at approximately 46-48 volts. In a large stadium where three phase power is available, it may be advantageous to select three phase transformers that, when rectified with a six diode bridge, will produce approximately 46-48 volts DC and produce the appropriate power in-bulk for an entire array of fixtures for a single pole. Where three phase power is not readily available, or in installations where the total harmonic distortion of current taken from the power utility is of concern, it may be more practical to use a power supply which takes line voltage in and delivers 46-48 volts DC out. Such power supplies capable of delivering 1000 watts of power are well known in the art and readily available.

In one alternate preferred embodiment where three-phase power is available, a transformer may be included to provide ballasting effect. With reference toFIG. 13, a schematic diagram for a ballasting transformer1310is depicted. Ballasting transformer1310preferably includes three elements: transformer1312; rectifier1314, and capacitor1316. Transformer1312may be a three phase 480V to 35V transformer known in the art. Rectifier1314is preferably a six diode bridge, collectively1318. Capacitor1316is preferably a 10,000 microfarad electrolytic capacitor. It is understood, however, that the three elements could be altered as known in the art by one of skill in the art.

Transformer1312inherently current limits. This is because the inductance of the winding in light of the operating frequency limits the output current of the transformer. The result being a transformer1310that provides the requisite power in-bulk for an entire array of fixtures for a single pole, or for a single fixture. As will be apparent to one skilled in the art, the circuit ofFIG. 13is also applicable when transformer1312is not self-ballasting. As the light is dimmed there will be some increase in the voltage output by the circuit. This will cause more heat loses in the transistors of the current regulator but will not otherwise effect the operation of the fixture.

In a preferred embodiment, as depicted inFIG. 14, a digital interface1410may be provided to connect a fixture or plurality of fixtures1414with a host1412for control and data collection. This digital interface1410with a host1412(computer) can be accomplished in any known manner, such as internet protocols (RS-232); via Ethernet; USB; or other suitable communication interface known to one of skill in the art. Digital interface1410could be either wired or wireless. The purpose of digital interface1410is for controlling the light fixtures collectively (such as depictedFIG. 1) and individually and may control, without limitation, input voltage/intensity/dimming of the LED array. The digital interface may also be useful for monitoring and keeping track of the operating conditions of each light separately or a pole of lights collectively. Operating conditions may include LED temperature, fan speed/air flow and other useful conditions. For example, a condition such as LED temperature may affect control functions such as fan speed of an individual fixture or conditions relating to a plurality of fixtures.

Digital interface1410allows the collection of data at host computer1412so that useful trends may be observed, in what may be known in other contexts as Statistical Process Control. The host computer1412preferably includes software that keeps track of the operating conditions/trends of the lighting fixtures1414. Keeping track of trends allows identification of failing systems before they become a larger problem or lead to fixture or system failure. For example, and not limitation, in a known temperature condition, such as 75° F., the software in the host computer may determine over time that the fan in the lighting fixtures has a normal operating range of a certain CFM (cubic feet per minute). The software in the host computer may additionally be programmed to detect when the CFM of the fan in one or more of the individually lighting fixtures is trending downward in the same (temperature) conditions. It can then alert an operator that maintenance of the lighting fixture(s) may be required before the fan or fans fail. As a result, the fan or fans may be either fixed or replaced before it/they fail which may in turn avoid failure of the entire LED array in the fixture. Thus, failure of a fixture during an event is avoided and costly repairs or replacement of entire fixtures can likewise be avoided. It should be understood that the specific example pertaining to the fan is for exemplification purposes only and that other operating conditions/data is contemplated and may be identified and tracked for trends as would be apparent to one of skill in the art (such as the ballast transformer1310ofFIG. 13discussed below).

As will be apparent to one skilled in the art, the inventive luminaire could also find broad use in architectural lighting. It should be noted that the asymmetric array of LEDs used to overcome inverse square fall off could be exaggerated to improve the look of the light at extreme angles of incidence as commonly found in building washes.

Finally, while preferred embodiments of the present invention have been described as employing a plastic Fresnel lens, the invention is not so limited. Obviously a glass lens could be employed to achieve identical results or the invention could be readily modified to use multiple lenses.