Table of Contents Hide
- 1 What Is a Track Light
- 2 Accent Lighting
- 3 Major Applications
- 4 Lighting Technology
- 5 Track Systems
- 6 Lighting Control
- 7 Design and Construction
- 8 Optical Design
- 9 LED Module
- 10 Color Rendering
- 11 Correlated Color Temperature (CCT)
- 12 Color Consistency
- 13 Thermal Management
- 14 LED Driver
What Is a Track LightA track light is an adjustable track-mounted luminaire that typically provides directional illumination to create a dramatic emphasis on the shape, texture, finish, and color of an object of interest. The trend towards flexible lighting concepts in constantly changing commercial environments calls for a versatile, adaptable and modular solution. Track lighting has been the preferred choice when it comes to lighting design for commercial showrooms, retail stores, art galleries and museums because it provides flexibility to cope with object size and architectural constraints. By marrying the latest in LED technology, track lighting makes differentiation, modelling and zoning simpler while redefining the standards of energy efficiency and pushing the boundaries of lighting performance.
Accent LightingTrack lighting is the dominant method of implementing accent lighting. Accent lighting is designed to create points of focus, establish a hierarchy of importance, and attract attention against the background of the general illuminance. Layering light is crucial to enhance visual perception of a space, maximize the use of the space, and create sense of visual direction in the space. Being the most important layer in the lighting composition, accent lighting reveals the three dimensional form of the space and establishes the importance of certain objects through the use of highlight and shadow. Track lights direct concentrated beams of light on objects such as paintings, sculptures and merchandise. The focal pool of light creates luminance contrast to reinforce design aesthetics. A rule of thumb to achieve the highlighting effect is that the luminance should be three times higher than ambient illumination.
Versatile track lighting has many virtues: it can be used to provide spotlighting, floodlighting, and wall washing. Spotlighting is used to accentuate a feature with high illuminance, creates attention and facilitates orientation. Spotlights produce narrowly focused beams of light to make select features pop out from the background. Track spotlights can be adjusted to focus illuminance on very specific areas, thus directing the viewer's attention. The contrast ratio of accent lighting to its surrounding ambience is typically 5:1. To sparkle (small bright spots in darker environment) or underline exclusivity of a feature, higher illuminance ratios of 15:1 or 30:1 are used. Spotlighting may be used in conjunction with perimeter lighting or floodlighting. Spotlights are classified by beam distribution. Typical beams for accent lighting include spot (10°-15°), narrow spot (6°-9°), or very narrow spot (5° or smaller). Floodlighting is characterized by a wide pool of light suitable for illuminating large objects or defining a large design element. Floodlights are classified as "narrow flood" (20°-25°), "flood" (30°-40°) and "wide flood" (55°-60°). Wall washing is a technique used to gently illuminate a wall or vertical surface. A smooth, even gradation flood of light flattens the visual appearance of the vertical surface.
Retail storesSuccessful retail lighting is about creating drama. Beyond fostering positive feelings of hospitality and comfort, lighting visually communicates quality, design, and features of merchandise. Mounted flexibly on tracks, accent lights based on LED technology deliver pools of light that add allure to high-end clothing, glamor to cosmetics posters, and luster to sparkling jewelry. By elevating the attributes of the merchandise, customers are encouraged to step inside the store, focus attention on the merchandise, and make their purchase decisions without consciously thinking. Track lights may be selectively moved and or oriented to highlight the merchandise or bathe the merchandise in even illumination. The flexibility of track lighting allows cost effective adaptation of accent lighting to the changing product ranges, campaign offers, and store layouts.
Showrooms and exhibitionsAccent lighting provided by track lights can make a big impact. The use of directional spotlights and floodlights enables the interplay of light and shadow that creates drama and depth in the space, and strengthen the aesthetic impressions of products and exhibits. Lighting can bring out the best in showrooms and items they illuminate. In today's hyper-competitive environment, leveraging lighting to evoke a sense of inspiration and create a more engaging experience is one way that leading brands distinguish themselves from the competition. Businesses are able to tell compelling brand stories and accentuate signature elements through visual merchandising in corporate showrooms and exhibition stalls. Lighting is a crucial tool for auto dealerships. Artfully designed light rounds out the appeal and personalities of cars, shows off the goniochromatic effect and sparkle of paint finishes. Track-mounted accent lighting delivers high controllable vertical and horizontal illumination that creates visual hierarchies within the environment, makes the display item charming and triggers impulses to buy.
Museums and art galleriesLight is needed in museums and art galleries to appreciate artwork, be it a historic artefact, contemporary art, 2D painting or 3D sculpture. Lighting design for art exhibitions must consider the interactive impact of lighting on museum occupants, artwork, and the environment. The qualities of light that should be addressed in museum lighting include intensity, distribution, color, movement, and aiming angle. Of the five qualities of light, the aiming angle has a significant impact on the enjoyment and understanding of the displayed artworks. The choice of from where light is directed towards the artwork will determine how artwork and architecture are revealed with light, and the form of artwork are modeled. For this reason, track lighting has been the method of choice the museum world because it provides maximum aiming flexibility to create a desirable pattern for optimal artwork modelling and visual comfort, and to bring out the key characteristics of the artwork.
Hospitality spaces and restaurantsTrack lighting allows users to function comfortably in restaurants. It complements blackout ceilings and put just the right focus on tablescapes no matter where the tables are positioned. Accent lighting can evoke emotion and add captivating atmosphere to intimate spaces, such as cocktail lounges, nightclubs, and dining areas. The interplay of light and shadow allows people to appreciate the aesthetic components of the space, inspires intimate dinner conversation, and brings the party to a perfect conclusion. Track lighting can be used to define zones, assign focused pools of light to specific zones and thus creates focal points and clear destinations.
Lighting TechnologyThe quantity and quality of illumination provided by track lights, the impression it creates about and the effect it has on the illuminated object are all factors in a successful accent lighting design. Aside from the economics, a variety of key characteristics of the light source must be considered when designing directional luminaires. Before the advent of LED lighting halogen and ceramic metal halide lamps had been the two primary light source implemented within track lighting systems. However, these light sources are challenged with not only the increasingly stringent energy codes and reliability requirements, but also the discriminating demands on the spectral quality and/or photometric performance that are of particular importance for interior accent lighting. Despite their superior color reproduction performance, halogen lamps have pathetic energy conversion efficiencies, short lifespans, poor optical controllability, and high probability of photochemical and thermal damage on light- and heat-sensitive materials. Ceramic metal halide lamps have improved energy efficiency and lifespan, but still produce optical radiation with unwanted wavelengths in the light spectrum as well as undesired beam performance.
LEDs rise to the challenge of directional lighting with ease. While high energy efficiency, long lifespan, exceptional controllability of light output, and solid state durability are their hallmark features, LEDs offer a number of additional advantages vital for accent illumination of merchandise and artifacts. The directional nature of LEDs enables high efficiency light extraction and optimal light distribution. LEDs are extremely flexible in spectral outputs. In museum and retail lighting, the choice of an illuminant's color appearance and color rendering performance will dramatically affect the color perception of the illuminated objects. The building block of all color characteristics is the spectral power distribution (SPD) which describes the relative amount of radiation at each wavelength of the visible portion of the electromagnetic spectrum. The SPD of LEDs can be designed to reflect all wavelengths of the visible light spectrum and reveal the colors of objects faithfully, matching or exceeding that of halogen and incandescent sources. The SPD of LEDs can be also tailored to produce any correlated color temperature (CCT) that complements the color scheme of an object or environment.
Another noteworthy advantage of LEDs is that they emit neither ultraviolet (UV) nor infrared (IR) radiation. UV and IR radiation is some of the least desirable aspects of conventional lighting and raises serious concerns: thermal IR energy can cause cosmetic products to deteriorate, fresh vegetables to dry out, chocolate and confectionery to melt; ultraviolet radiation is likely to cause photochemical damages to objects containing light sensitive materials and result in color fading or shifts. To mitigate damages of photochemical action, the Commission Internationale de l'Eclairage (CIE) recommends to exclude UV and IR light with protective filters and limit illuminance to 50 lx for materials that have medium and high responsivity to light. LEDs produce UV-free cool light, making them a great fit for accent and display lighting in museums, galleries, food stores, fashion shops, and environments where UV and IR radiation should be avoided.
Track SystemsThe track system is designed to adjustably accommodate the track heads (track luminaires) and thereby provides the power supply and structural support thereto. The track is usually made of extruded aluminum that resembles an "H" in cross section. Track systems are available in one-circuit or multiple-circuit configurations. Copper conductors are co-extruded in PVC insulators to form a continuous electrical raceway for the circuit. Each circuit is typically rated for a 20-amp load. The multiple-circuit tracks may either share a common neutral or come with separate neutrals. Independent neutrals enable greater power capacity, consistent dimming performance without generating harmonics or interference on the neutral conductor. Sharing neutrals in some cases may cause voltage-drop interaction between multiple branch circuits, and neutral conductor overloading. The track luminaire may be fixed to any point along the full length of the track using a track adaptor. The track adaptor typically has features that enable safe and robust mechanical and electrical connections. Tracks are joined for continuous runs in various configurations using I-, L-, T- or X-shaped intercept connectors. They may be surface-mounted or recessed to an architectural surface, such as a ceiling or a wall, or may be suspended from the ceiling.
Lighting ControlTrack systems can be controlled either as non-addressable systems or addressable systems. A non-addressable system may falls into one of three types: simple switched circuit, simple dimmed circuit, and complex or automatically controlled circuit. All luminaires mounted on the control circuit will respond in the same fashion. Addressable track systems allow individual control of single luminaires or discreet groups of luminaires, independent of the section of tract or circuit to which they are connected. The individually addressable control is accomplished through data control over data lines, wireless data control, or data control over power lines. Data control over data lines or power lines are implemented by using a protocol such as DALI or DMX. DALI light control is widely used in addressable track lighting systems. This protocol enables bidirectional communication over a 2-wire control and allows non-volatile memory of settings, such as broadcasting, group assignments, and individual control, to communicate specified actions. Wireless lighting control requires the use of wireless communication modules (receivers) that are integrated into the luminaires. Such luminaires can be individually accessed and controlled from a handheld device or via a mobile app through a protocol such as ZigBee, Bluetooth, or Z-Wave.
Design and ConstructionRetrofit track heads and the early versions of new construction LED track heads have a straightforward design. The luminaire is an assembly of a swiveling and rotating housing or frame and a directional LED lamp in the form factor of PAR20, PAR30, PAR38, or MR16. The latest generations typically embrace an integrated design: the entire luminaire is designed around an LED module. Integrated design of track luminaires allows more efficient thermal management, precise optical control, and advanced lighting control. Most track luminaires feature a die cast or extruded aluminum cylinder housing which facilitates heat exchange between the LED module and the surrounding environment while providing a sleek architectural look. The driver and control gear may be installed into the same housing with the optics, LED module, and thermal management system, or are mounted in an auxiliary gear box. LED track heads may also come with a low profile design in square or flat cylinder shapes. This type of luminaires is usually designed to provide a large light emitting surface (LES) for uniform illumination of large targets. The aluminum housing is electrostatically applied with a corrosion resistant polyester powdercoat finish after a multi-stage conversion cleaning process.
Optical DesignThe object of the optical design is to regulate luminous flux from the light source for a desired light pattern. To create contrast and drama with spotlighting, the output from the LEDs should be controlled to produce a tight, clean and punchy beam. It is essential that the maximal amount of emitted light is delivered to a targeted area and creates point of interest. Therefore the optic design objective of an LED spotlight is to focus on the center beam candle power (CBCP) and the field-to-beam ratio. CBCP refers to the luminous intensity at the center of the beam, which is the point of maximum intensity for most symmetrical beams. The field-to-beam ratio helps identify the hard beam (which has a clean, well defined pattern) or the soft beam (which fades gradually out toward the edges). The beam angle is the angle between two directions for which the intensity has fallen to half its peak value. The field angle refers to the angle measured from which the intensity is 10% of the maximum beam intensity. In contrast to spotlighting that emphasize its CBCP punch, floodlighting and wallwashing call for a uniform light distribution (high center-to-edge color consistency) so that no shadows will obscure important details.
Directional LED luminaires utilize reflectors or total internal reflection (TIR) optics to capture and redirect light emitted from LEDs. Optical reflectors are simpler to implement and less expensive to manufacture when compared with compound lenses. They are made from anodized pure aluminum or optical grade metalized polycarbonate designed for high temperature conditions. Efficient control of the light output from a directional light source with a reflector requires higher levels of reflector precision. Reflectors for track luminaires are usually faceted or segmented to ensure better distribution of luminous flux to the desired direction. This type of optics, however, will only control the rays that hit the reflective surface, ignoring the portion of the beam that is not incident on the optic. To produce smooth circular beams with an FWHM divergence angle between 10 and 35 degrees, TIR lenses are an optimal solution. These compound lenses capitalize on characteristics unique to LEDs by combining the best of both a reflector and a lens. A refractive lens captures, concentrates and directs light to a reflector which shapes the beam in a desired angle. Injection-molded from polymers such as polycarbonate and acrylic, TIR lenses can be sculpted to a precise beam pattern with a high optical efficiency.
Track luminaires may be equipped with various optical accessories to change the photometric performance in a desired way. A factory or field-installed accessory holder is designed to accommodate these accessories. Glass spread lenses are used to change the direction and control the distribution of light rays. Beam softeners remove hard edges and spread light homogeneous. Dichroic glass filters allow only very narrow bands of energy to be transmitted for the light source and thus enable luminaires to produce light with minimal UV and IR, or discrete visible wavelengths for very saturated colors. Louvers and hoods eliminate high angle glare, making light beams disappear in downlight applications. The glare control devices are painted optical matte black on the inside in order to reduce reflected glare from the control device itself. Light reduction screens allow light output to be reduced without shifting the initial CCT of the light source.
LED ModuleAn LED module is an assembly of light source on a metal core printed circuit board (MCPCB) or a thermally conductive, electrically insulated substrate. The light source can be ceramic-based high power packages, chip-on-board (COB) packages, or mid-power packages. High power LEDs come with a robust thermal design that allow high current density operation for high lumen outputs, with excellent lumen maintenance and color stability. Mid-power packages, despite their high initial efficacy and low cost, are prone to thermal degradation due to their use of the plastic leaded chip carrier (PLCC) packaging platform. COB LEDs are the most widely used types of LED packages in directional lighting applications. These multi-die LED arrays are capable of producing a high volume of lumens from a single package, with a high CBCP and illuminance uniformity desired for accent illumination. Direct bonding of LED dies to the MCPCB or ceramic substrate allows efficient heat transfer from the LED junction to the heat sink. The Zhaga Consortium has standardized a family of form-factors in an effort to address the complexity of accommodating a wide range of COB LED modules.
LED packages are typically soldered onto MCPCBs. An MCPCB construction consists of a top copper layer that acts as a circuit layer for electrical connections, a dielectric layer that offers both electrical isolation and thermal conduction, and an aluminum substrate that performs as a heat spreader. The formation of high reliability solder joints between the LED packages and MCPCB is very critical in ensuring the integrity of electrical and thermal path. Solder joint reliability depends on the solder alloys, reflow profile, and the metallization of the LED package and MCPCB. COB devices are available with solderless connector solutions. The use of a solderless, Zhaga-compliant COB connector to attach a COB LED to a heat sink simplifies the mechanical fastening of the LED package to the heat sink, and helps ensure consistent optical alignment of the secondary optic with the LES.
Color RenderingColor rendering refers to the interaction between the spectral power distribution of a light source and the spectral reflectance function of objects. The spectrum of light determines how object colors are rendered. The ability of a light source to faithfully reproduce the object colors is critical to retail and museum lighting applications. The color rendition of a light source can greatly affect what information people receives from the merchandise or exhibit on display. A high color rendering light source requires there's a right amount of spectral content in every wavelength throughout the visible spectrum from 400nm to 700nm. Common white LED sources are generated with blue pump LEDs. The color reproduction performance of these LEDs depends on the composition of the phosphor which down-converts the wavelength of some of the blue light into longer wavelengths for a broad yellow-orange spectrum.
The reliance on a phosphor down-converter to alter the SPD of LEDs introduces a trade-off between luminous efficacy and color quality. The use of a broad bandwidth phosphor down-converter to achieve a good color rendition with LED lighting compromises the luminous efficacy of the LEDs since the energy of the derived photon is lower than the original short wavelength photon. As expected, most consumer LED products comes with a mediocre color rendering performance because the consumer lighting market is more sensitive about price. The tradeoff of low luminous efficacy for high color quality and the use of broad bandwidth phosphors translate to a significantly high cost of high color rendering LEDs when compared with their low color rendering counterparts. Nevertheless, retail, hospitality and artwork display lighting requires artificial illumination with a color rendition comparable to that of sunlight or incandescent radiators, which have an SPD uniformly spread throughout the visible spectrum.
The color rendition of a light source is currently assessed by the color rendering index (CRI), a color fidelity metric that compares the rendered colors of 14 test colors being illuminated by a light source to the rendered color of the same set of test colors being irradiated by a black body radiator. The general color rendering index Ra is simply calculated as the average of Ri for the first eight color samples (R1 – R8) that have medium color saturation. The CRI has a maximum value of 100. As a reference, daylight has a CRI of 100, with incandescent and halogen bulbs being relatively close. A minimum CRI of 90 is usually required for high color fidelity lighting. However, CRI Ra does not include the value for the highly saturated color samples (R9 - R14). As rendition for strong color tones is of high interest for museum and retail applications, values for R9 through R14 should be specified separately in addition to CRI. Among the saturated colors, R9 is of vital importance to bring out the color characteristics of skin tones, merchandise and artwork. R9 values above 75 is considered excellent. Because of the deficits of current CRI calculation, supplements and alternatives are being developed or introduced. New methods or standards for evaluating color renditions include TM-30, color quality scale (CQS), gamut area index (GAI), etc.
To achieve higher performance in color reproduction, violet pump LEDs are gaining favor in a number of high-end lighting applications. Violet pump LEDs deliver radiant power fairly broadly across the wavelength range of the visible radiation spectrum, without the blue peak that comes with blue pump LEDs.
Correlated Color Temperature (CCT)The correlated color temperature (CCT) of a light source is a very important characteristic that most consumers and even lighting suppliers are not aware with. The color appearance of light affects subjective interpretation of brightness. Light exhibiting a CCT in the range of 2700 K to 3500 K is referred to as having a "warm white" appearance. "Neutral white" light falls in the range of 3500 K - 4100 K, and light with a CCT above 4100 K is referred to as having a "cool white" appearance. Warm white lights is reminiscent of the sunset or a flame, and helps foster a relaxed and intimate ambience. Neutral white light has a balanced color appearance, whereas cool white light makes people feel more energized and refreshed. When it comes to atmospheric lighting in restaurants, hotels, and high-end residences, warm white light is best suited because it enhances reds and oranges to strengthen the attractiveness of the environment, and is most flattering to skin tone.
Light has a biological effect. The higher the CCT, the higher percentage of blue contained in the light spectrum. Blue light is known to stimulate the non-visual photoreceptor in the eye, the intrinsically photosensitive retinal ganglion cells (ipRGCs). At high dosages of blue radiation, the ipRGCs can signal the SCN master circadian clock to suppress the release of the sleep hormone melatonin while increasing secretion of dopamine, cortisol and serotonin which help the body to prepare for the day's activity. As a result, the selection of light source CCT must take the biological effect of light into account. Ill-timed exposure to high CCT light, e.g., in the evening and night, can disrupt circadian rhythm which may lead to a number of negative health consequences. High CCT light (under 5000 K) are generally used for interior illumination during daytime. In residential and hospitality spaces, warm white light is more appropriate for ambient lighting.
Aside from photochemical action trigged by IR and UV radiation, excessive radiation of short wavelengths poses a high damage potential to light-sensitive materials due to the excitation state of molecules and high energy level of photons. For this reason, museum and gallery lighting typically uses low CCT light source which radiates less high energy photons than high CCT light.
Color ConsistencyBinning is a way of sorting LED packages so that all products from a specific bin produce optical radiation with the same color appearance and a similar light output. LEDs are binned for their color (chromaticity), brightness (luminous flux), and sometimes forward voltage. Color binning is particularly important because the chromaticity of LEDs from a single production can fall into a wide variety of categories as a result of the variability that is inherent in the manufacturing process of phosphor-converted LEDs. How much color variability is acceptable depends on the application. Museum and retail lighting requires the tightest color control of light produced from different luminaires, modules and packages, among all lighting applications. The color consistency of LEDs within a bin can be measured using the Standard Deviation Color Matching (SDCM) method or the American National Standards Institute (ANSI) method. Most museum applications requires a color uniformity of 0.0002 ∆u'v' (ANSI Duv value) between luminaires, which is much tighter than 1-step MacAdam ellipse or 1xSDCM (approximately 0.007 ∆u'v' or ±30 K @ 3000 K CCT). LEDs for high-end retail and hospitality lighting are typically binned to a 2-step MacAdam ellipse tolerance (approximately 0.001 ∆u'v').
Thermal ManagementThermal management is one of the key determinants of achieving the reliability expected from LED lighting. LEDs generate a significant amount of localized heat due to non-radiative recombination, the Stokes loss, and light extraction losses. The Stokes loss, which is generated during the wavelength down-conversion process, is particularly high in LEDs used for track luminaires which are typically equipped with high CRI, and low CCT LEDs. During the operation of these LEDs, a huge portion of short wavelength light needs to be down-converted to longer wavelength light, and this process produces a considerable amount of Stokes heat. Without thermal management, the junction temperature of the LED will climb and give rise to a number of failure modes. Operating LEDs beyond the maximum rated junction temperature will accelerate lumen depreciation and color shift. Accent illumination of artwork and merchandise is very sensitive to color shift. Museum applications may require the color shift tolerance to be controlled within 0.003 ∆u'v' over five years.
The ability of an LED track light to dissipate heat rests with the conductive and convective cooling capacity of the thermal path. Thermal conduction design centers on maximizing material thermal conductivity and heat transfer surface area of the thermal path. Efficient convective cooling is dependent upon the surface area of the heat sink boundary and the mobility of the air flow around the luminaire. The heat sink is made from extruded, die cast or cold forged aluminum. The die cast process allows a sleek, aerodynamic design that maximizes the convection heat transfer coefficient while enhancing the aesthetic appeal of luminaires. A thermal interface material (TIM) is usually placed between the MCPCB and the heat sink to minimize the interfacial thermal resistance and facilitate heat spreading across the heat sink.
LED drivers may be designed to support both phase control and DC dimming. DC dimming is based on constant current reduction (CCR), pulse-width modulation (PWM) or a combination of them. The CCR and PWM methods allow LED luminaires to produce smooth, deep, responsive dimming in DALI, DMX, ZigBee, and 1-10V systems.