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Bring the Dynamics of Games to LifeSports lighting is designed to create optimal visual conditions for athletes, contribute to an engaging experience for spectators, and help bring the spectacle and dynamics of games to life through television broadcasting. Being a part of the civilization and an important cultural thread in the fabric of society, along with their recreational attribute, professional and recreational sports have received high and growing levels of attendance, participation, and enthusiasm from the general public. The positive impact of sports on the economic development and urban growth has been driving an ongoing growth in the demand of facilities to accommodate sporting activities. A consequence of this is the springing up of stadiums and arenas all over the world. Sports are also an important part of school education, community interaction and institutional development. Athletic fields, gymnasiums and other sports facilities commonly are part of educational facilities and municipal recreation centers. As a critical part of sports infrastructure, lighting serves to provide an appropriate luminous environment for people enjoying or participating in professional competitions/training or leisure time activities in these facilities.
Sports FloodlightingIn lighting design for outdoor sports facilities, floodlighting is the only resort. This is because lighting installations for these facilities are often located outside the boundaries of playing areas. Since there're no overhead structures available for hanging light fixtures and no surfaces to redirect the light bounced from the playing area, outdoor sports lighting relies on direct distribution floodlights to provide controlled field illumination. Floodlighting is also the principal lighting technique for illuminating arenas, which are large, multipurpose facilities. This type of indoor venues has a large seating capacity and therefore needs floodlighting to provide adequate illuminance from multiple positions and viewing angles that does not cause glare to both players and spectators.
Floodlighting serves multiple roles in sports lighting design. Floodlighting luminaires can project a beam over a long distance to illuminate specific geometric areas. This allows the luminaires to be mounted on high masts or structures that are remotely located to avoid conflict with any functional elements in the facility. Locating the luminaires away from the most frequent directions of plays and spectators also eliminates direct glare. By incorporating a balanced combination of key light, back light and fill light, directional illumination from multiple locations reduces harsh shadows and provides uniform horizontal illuminance while allowing the lighting design to include modeling. A well modeled playing area reveals the three-dimensional image of an object, e.g., a ball, target, or a player.
Overhead lighting from high bay luminaires provides only downward illumination that contributes mainly to horizontal illuminance, whereas directional floodlighting can provide the critical vertical illuminance over the height of the entire playing area of multi-directional aerial sports, along with uniform horizontal illuminance. Multi-directional aerial sports involve playing with an object that is in the air at least part of the time. These sports include soccer, football, basketball, baseball, volleyball, tennis, cricket, platform tennis, lacrosse, softball, handball, racquetball and squash. High vertical illuminance is also important for uni-directional ground level sports where the playing object is aimed at a fixed target near ground level. Typical outdoor uni-directional ground level sports include track and field, motor racing, bicycle racing, bicycle motocross (BMX) racing, horse racing, dog racing, drag racing, skiing, and ice skating.
Light DistributionA floodlight is an aimable luminaire that is designed to produce directional lumens in a well-controlled beam. Floodlights are available in a multitude of light distributions ranging from narrow field angles (for illuminating sports fields at a distance) to wide field angles (for illuminating close-up areas). A field angle is defined as the angle between the two directions for which the intensity of light is 10% of maximum as measured in a plane through the nominal beam center line. In floodlighting designs, the field angle is known as the beam spread. Beam spreads are classified by a NEMA designation as Type 1 to Type 7.
- Beam type 1: 10° to 18° (Very Narrow)
- Beam type 2: > 18° to 29° (Narrow)
- Beam type 3: > 29° to 46° (Medium Narrow)
- Beam type 4: > 46° to 70° (Medium)
- Beam type 5: > 70° to 100° (Medium Wide)
- Beam type 6: > 100° to 130° (Wide)
- Beam type 7: > 130° and up (Very Wide)
The horizontal and vertical beam spreads, which is available in either asymmetrical distribution or symmetrical distribution, are dictated by luminaire location and the task sizes being illuminated. Floodlights use fixed mountings but usually come with rotation and tilt adjustment provided by mounting adapters such as knuckles, slipfitters or yokes. The field illuminance distribution is controlled by a combination of optics internal to the luminaire and orientation of the luminaire. The beams can be further refined to minimize obtrusive light by using internal/external devices such as shields, louvers and baffles.
A Farewell to HID LightingMany factors need to be considered at the time of selecting a luminaire to facilitate proper lighting design. Good sports lighting should be responsive to needs of game participants, spectators, TV broadcasting, as well as facility operators who persistently seek to reduce the cost of lighting. It is then important to go with a technology that has the best potential to address the lighting design challenges. Over the past few decades, metal halide (MH) lamps had been the light source of choice for sports lighting. Before the advent of LED lighting, metal halide lamps were the most economical choice as a high wattage light source. Another high intensity discharge (HID) light source, high pressure sodium (HPS), offers a very competitive source efficacy as compared with the MH counterpart but the extremely poor color rendering performance prohibited its use in sports lighting.
The use of metal halide lamps for high lumen sports lighting, however, involves many compromises. This light source fails to synchronize with today's ever-stringent energy efficiency standards, lighting quality criteria and environmental sustainability requirements. Aside from the efficiency, life cycle and color rendition imperfections, achieving good illuminance uniformity with MH luminaires for arena and stadium lighting would be unimaginable without using a large number of luminaires.
The illumination criteria of sports facilities are grouped into four classes: Class I (facilities with spectator capacity no less than 5,000), Class II (facilities with spectator capacity under 5,000), Class III (facilities with spectator capacity up to 2,000), and Class IV (facilities with limited or no provision for spectators). Higher the seating capacity, higher the required the quantity and quality of illuminance. Among the factors that define the quality of illumination, uniformity ratio (UR) is particularly important. Major events such as soccer, football, baseball, and basketball games require a very low uniform ratio (maximum-to-minimum illuminance). For example, the maximum UR for Class I soccer play is 1.7:1, and the UR requirement for Class I baseball competition is even more stringent - 1.2:1! This places a high demand on illuminance uniformity of luminaires. Unfortunately, gaseous discharge bulbs have a very poor uniformity (6:1 typical). To meet the UR requirement of games held in arenas and stadiums, a high density mounting of metal halide luminaires is need. This can be a tremendous investment.
Sports lighting provided by metal halide fixtures is also burdened by a number of notorious problems. The hot restrike process which can take up to 20 minutes is of greater concern than initial start-up. A momentary loss of power can result in a long period of blackout during the game. For TV broadcasters, flicker can be a problem of magnetic ballast equipped metal halide lights should camera frame rates rise to the neighborhood of 120 frames per second. Over a period of use, the quart arc tube of metal halide bulbs gets weak, chances for envelope failure (bulb explosion) are always there since the bulb operates at high pressures (520 to 3,100 kPa) and very high temperatures (900 to 1,100 °C).
Solid State LightingLEDs offer leap-forward improvements over metal halide lights in all of the aspects essential to sports lighting, including the most concerned total cost of ownership (TCO). The semiconductor based light source employs the principle of injection electroluminescence to produce high efficiency energy conversion from electrical power to optical power. Sports lighting systems can consume large amounts of power and over time the energy cost can be more significant than the first cost of lighting equipment. With the ability to deliver luminaire efficacies well over 150 lm/W, LED flood lights offer substantial energy savings over metal halide lights which even struggle to get half the luminaire efficacy of LED systems. The energy savings of LED sports lighting systems can be maximized when the digital controllability of LEDs are exploited. The high return on investment (ROI) with LED lighting is reflected not only in low energy consumption, but also in its virtually zero maintenance over a life cycle that can be 3 to 10 times longer than that of metal halide fixtures.
Sports lighting designers no longer have to prioritize a very limited number of factors as with HID lighting. All critical design factors such as visual performance, color quality, glare control, and lighting control can be addressed simultaneously at a low TCO. LEDs, with their directional and compact nature, allow precise and efficient regulation and distribution of luminous flux with custom optics for low glare, uniform light distribution. The use of multi-LED configurations and lens arrays lends LED systems a high uniformity of light distribution, improving the uniformity ratio with HID lighting by more than a factor of two. High illuminance uniformity with LED lighting results in drastically reduced fixtures on an installation. This can be substantial savings for large sports facilities burdened with stringent uniformity requirements. Spectral versatility of LEDs from the use of phosphor wavelength down-converters allows LED sports lighting systems to reproduce colors faithfully and tailor the most appropriate correlated color temperature (CCT) for the best on-site ambience and broadcasting effects. The instant on/off capability and excellent control dynamics of LEDs take lighting control to a whole new level of user interactivity.
No fragile glass, no hazardous mercury, no hot quartz that can cause ignition of flammable materials, and no emission of ultraviolet light, LEDs offer an environmentally and photobiologically safe solution. Made from a block of semiconductor, the solid state light source possesses greater resistance to shock, vibration, and wear.
Luminaire DesignSports floodlighting systems are highly integrated assemblies of light sources, optics, drivers and controls, with thermal management and system protection running parallel to performance engineering. High power LED flood lights are designed as either integrated systems or modular systems. An integrated LED luminaire is a self-contained system that integrates all functional components into a weatherproof assembly. A modular floodlighting system consists of multiple LED engines which are driven by an external power supply. The modular LED engine is basically a thermally managed optical assembly that has the same level of enclosure integrity as that of an integrated system. There're no noticeably differentiated pros and cons between two types of systems. Modular systems provide scalability for light output and versatility for optical aiming from a single fixture. They excel in design continuity and cost efficiency for projects involving use of multiple lumen packages and/or optical configurations while allowing convenient servicing and replacement of light engines and LED drivers. Integrated systems, with co-located power supplies, typically offer higher visual integrity in appearance and are often tailored to a more specific type of applications.
LED flood lights come with a housing-as-heat-sink design. The heavy duty housing is typically constructed of die cast aluminum for high heat sinking performance, mechanical strength, dimensional consistency, and corrosion resistance. The integrated type luminaires usually have separate driver compartments which thermally isolates the electrical components from the LED array and allows quick and easy servicing. The optical compartment of both integrated and modular systems are typically protected by a heat and impact resistant tempered glass lens which also enables self-cleaning of dust and dirt. A die cast door/lens frame secures the glass lens to the housing. The optical compartment, driver compartment, and other points of entry and material transition are all thoroughly sealed and gasketed to resist ingress of dust, dirt and humidity. A membrane vent is typically integrated to the housing to equalize pressure differentials within sealed enclosures. Pressure equalization reduces seal fatigue and explosion hazards while blocking water and contaminants that would depreciate the lumen output of the LED array and cause degradation in LED package materials. To resist fading and corrosion from salt and UV exposure, the aluminum housing is finished with a durable polyester powder coating electrostatically applied after a multi-stage cleaning, pretreatment and chemical conversion coating process.
Light SourceLEDs are packaged devices in which LED chips are provided with mechanical support, electrical connection, thermal conduction, wavelength down-conversion, and polymer encapsulation. These package elements protect the semiconductor chip from direct environmental exposures, interface it to its operating system, and alter its spectral characteristics. There are different LED package designs available on the market, which include mid-power packages, high power packages, and chip-on-board (COB) packages. The selection of package platforms is a critical start to the performance and reliability of the lighting system. Mid-power packages have a dominant presence in the lighting market because of their high luminous efficacy and low manufacturing cost. However, these products should not be considered for sports lighting applications as their plastic housing and vulnerable electrical path cannot withstand high thermal and electrical stresses in high wattage sports lighting systems.
As opposed to mid-power packages that suffer from accelerated lumen depreciation and color shift at junction temperatures of above 100°C, high power LED packages have a robust platform that offers them high drive current capability. This high flux density light source is designed to deliver dependable performance at junction temperatures of up to 150°C. The high temperature reliability of high power LEDs can be attributed to their ceramic construction which is fundamentally superior to plastic packages. Ceramics are also optically and chemically inert, which lends high photostability and chemical stability to high power packages. Mid-power LEDs have an unreliable interconnect design that makes them susceptible to electrically open failures caused by temperature cycling, electromigration due to excessively large current, or environmental stresses. In contrast, the anode and cathode pads of high power LEDs provide a large solder footprint that allows the LED assembly to meet strict solder joint reliability requirements. All these advantages make high power LEDs the best choice for sports lighting applications.
Sporting lighting has a unique requirement when it comes to the spectral characteristics of light. A light source that faithfully reproduces the colors of objects can enhance the visual experience of spectators and visual performance of participants. Metal halide lamps have a typical color rendering index (CRI) of 65, which is tolerable but far from perfect. LEDs available the market have a minimum 70 CRI and can be spectrally optimized to achieve a CRI greater than 90. The CRI color system was developed for human vision. Television recording and broadcasting often take place in large sports venues. A light source with a reasonable CRI can render colors poorly for a video camera because response curves of video sensors are quite different from those of the human eye. As a result, the television lighting consistency index (TLCI) has been developed to provide a color rendering metric for television and video cameras. In general, video recording requires a light source with a minimum TLCI of 85. With broadcasting in HD, 4k, and even 8k HDTV, there is now a need for a high TLCI so that the HD video sensor in the camera can capture images with vivid, truer-to-life colors.
Color temperature is a characteristic of visible light that will affect the visual appearance of the environment. The correlated color temperature (CCT) for sports lighting applications generally falls within the cool white range (4000K to 6500K) because the light spectrums in this range contain a high percentage of blue wavelengths. Blue-enriched white light promotes concentration, alertness and attention, making players and spectators feel more energized and refreshed during the game. Venues for different types of sports may have varied color schemes for the playing fields and architectural elements. Hence lighting should be provided with a best suitable color temperature to enhance color contrast, visual perception, ambience and aesthetics. For example, sports played on turf and blue surfaces such as soccer, football, baseball and golf require cool white lighting in the 5000K - 6000K range, whereas sports played on wooden surfaces, such as basketball and volleyball, will look best under slightly warmer CCTs (around 4200K). There is a consensus in the photographic industry that 5600K is the standard CCT for outdoor lighting and most video and photography equipment are designed to work optimally at this CCT. As such, outdoor sports venues typically have their lighting designed to support 5600K.
LEDs can be packaged to produce any CCT desired. For multi-use facilities that play sports with varied CCT requirements, tunable white LED technology allows dynamic control of CCTs from a single luminaire. Care should be given to the color consistency of the LEDs. Due to manufacturing tolerances, temperature variations, and varying drive currents, there can be huge variations of color and brightness of a particular group of LEDs. Small binning tolerances remain essential to maintaining a tight color point across all luminaires installed in a project.
Optical SystemThe optical design of sporting lighting systems should place an extra emphasis on uniform and precise light distribution. High illuminance uniformity ensures the visual perception of playing target will not be distorted both in speed and position while maximizing effective illuminance coverage. A clean beam of light contributes to precise spreading of illuminance to an intended area without causing excessive spill light. Conventional systems use a system-wide reflector to regulate luminous flux from the light source. However, the light engine of modern sports floodlights consists an array of directionally emitting LEDs. A single reflector fails to efficiently and effectively distribute and control the light emitted from all LEDs.
High power LED flood lights are generally designed with a reflector matrix or lens array. The integrally molded optics provide individual optical control of the LEDs while ensuring consistent optical alignment when indexed to the circuit board. Lens arrays, which can be made from polycarbonate (PC) or polymethylmethacrylate (PMMA), are assemblies of compound lenses designed to provide total internal reflection (TIR). The lens assembly includes a refractive lens that efficiently bend the light rays at the required angle. A reflector then collects the light from the refractive lens and sends it out in a controlled beam. TIR optics provides high efficiency light extraction, high uniformity light distribution, and tight beam control.
In high wattage sports lighting systems the LEDs often operate well above 100 °C and the temperature at the phosphor layer is even higher due to Stokes shift and light absorption. Therefore, thermal stability of the TIR optics should be considered because the lens array is mounted in close proximity to the LEDs. PMMA (acrylic) has poor resistance to heat at temperatures above 90°C. Polycarbonate resins can withstand temperatures up to 120°C. In extreme temperature conditions, silicone lenses (maximum permanent operating temperature 150°C), glass lenses (temperature stable up to 400°C), or aluminum reflector matrices can be a more reliable solution.
Thermal ManagementWhile the rated service life of LED packages is projected to be from 50,000 to as much as 200,000 burntime hours, the system life of an LED flood light can be as short as the life of conventional systems if the luminaire is not properly designed and engineered. Many failure mechanism of LEDs are initiated by excess heat buildup within the package. Electroluminescence and photoluminescence are two fundamental mechanisms of LED light generation. They are also the heat generating processes which convert up to half of the electrical energy fed to the LEDs into thermal energy as a byproduct. Heat flux concentration at the packages can causes phosphor efficiency degradation and encapsulant yellowing, which result in lumen depreciation and color shift. Operating LEDs beyond their maximum rated junction temperatures will lead to a 30 to 50 percent decrease in their useful life for every 10˚C increase. Thus, maintaining the junction temperature of LEDs below the failure point is a prerequisite to long life, dependable operation of LED systems.
Thermal management for LED luminaires counts on a systems approach. As noted previously, use of LED packages with high temperature capability is critical because the reliability of thermal path from the semiconductor junction to the board interconnection interface varies significantly for LEDs with different package platforms. High power packages can survive high thermal stresses and are designed with a robust thermal path, while mid-power packages have poor thermal resistance and the path from the junction to the circuit board has a number of failure factors. It must be noted that, solder joint reliability is of utmost importance as the solder interconnect is influenced not only by thermal and electrical loads, but also by environmental loads and temperature cycling. In particular, the coefficient of thermal expansion (CTE) at solder interconnects must be kept very low as sports lights installed in the outdoor environments can experience repeated temperature cycling.
A metal core printed circuit boards (MCPCB), a thermal interface material (TIM), and a heat sink (luminaire housing) form the system-level thermal path. The MCPCB, which consists of a number of layers including a dielectric sandwiched between two metal layers, offers high through board thermal conductivity. The TIM is placed between the MCPCB and heat sink to minimize the interfacial contact resistance. Passive thermal management is the dominant strategy used in LED sports floodlights. This means the performance and reliability of an LED flood light is determined by the ability of a heat sink to conduct and convect thermal energy away from the LEDs to the ambient through its natural thermodynamics. Aside from thermal conductivity and physical volume, the surface area of the heat sink should also be maximized to facilitate the convective cooling. Moreover, an aerodynamic design will increase airflow over the exposed surface area of the heat sink. Attention should be paid to overdesigned heat sinks which have a high density of deep fins. This type of mechanical design can encourage debris accumulation and compromise the housing's self-cleaning performance.
LED DriverThe LED driver is the central nervous system of an LED luminaire. LEDs are current driven semiconductor devices with a negative temperature coefficient. The LED driver rectifies AC power into DC power which is then converted into a constant current capable of driving the LEDs for a desired output, regardless of changes in the supply voltage or LED forward voltage. The efficiency of the LED driver is an important part of system efficiency. It may also play a significant role in determining the thermal stresses of the system because the energy loss during power conversion is dissipated as heat. High power LED systems must be operated by constant current drivers which use a switch-mode power supply (SMPS) to regulate output to the LEDs. The SMPS ensures a very high driver efficiency (up to 98%). The disadvantage of switching power supplies is that they produce electromagnetic interference (EMI) radiation which requires additional filtering circuit to mitigate. Line-operated lighting systems must employ a power factor correction (PFC) circuit to maintain a high power factor (PF) and low total harmonic distortion (THD).
When it comes to LED driver design for sports lighting systems, of particular concern is flicker mitigation. Flicker in sports lighting affects speed of playing target and video recording quality. At higher frequencies, flicker may no longer be directly visible but can give rise to the stroboscopic effect. The stroboscopic effect creates an optical illusion which causes the motion of the playing object, such as a flying ball, to be wrongly perceived. Another problem with LED flicker is that dark bands can occur in the recorded video when modulation interferes with the shutter speed or video scan rate. A low flicker index should be maintained for sports lighting to accommodate video shooting at 120fps. High profile sporting events often employ slow motion cameras with frame rates in excess of 1000fps, which poses greater challenges to mitigation of high-frequency, invisible flicker. Flicker is reduced by filtering out output ripple using capacitors.
The LED driver needs to execute a range of sub-tasks sequentially or in parallel to provide tight regulation and dynamic control on the current output. Additional protection features, such as overcurrent, short-circuit, overvoltage and over-temperature protections, are provided to reduce the risk of failure. In order to adequately protect sensitive circuits and components in LED drivers from damages of transient voltages, a surge protection device (SPD) is usually installed ahead of the LED driver. The driver circuit is completely sealed against moisture and environment contaminants.