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What Is a Shop Light
LED shop lights refer to a family of utility light fixtures that provide general lighting and/or task lighting in commercial, industrial, and retail environments. Designed to deliver direct light to the work plane or floor, shop lights are the workhorse in low bay applications which typically have a mounting height less than 15 feet above the floor. They find particular use in workshops, warehouses, utility rooms, grocery stores, parking garages, basements, offices, and other interior spaces where economy, practicality and scalability of lighting are essential considerations.Fixture Design
While shop lights of various form factors are available today, the most commonly mentioned shop lights are linear light fixtures which were originally designed to hold T5, T8, or T12 fluorescent lamps. These flush-mounted, pendant-mounted or workstation-integrated linear luminaires can be divided into two categories: strip lights (strips) and wraparound lights (wraps). Strips are simple metal channels with exposed fluorescent tubes or linear LED assemblies (LED tubes or integrated LED modules). These luminaires generally use reflectors to help direct light out of the fixture. Wraps are mostly utilitarian but have a diffuser or prismatic lens that covers the face of the fixture. This cover is intended to obscure direct view of the light sources (fluorescent tubes or LEDs) and protect the light source from dirt and debris. Shop lights are available in a nominal length such as 2 ft, 3 ft, or 4 ft. There're luminaires that can be joined for straight continuous runs. Workstation-integrated shop lights typically have an on/off pull chain switch or rocker switch at one side of the fixture.Lighting Technology
Fluorescent light fixtures have been employed ubiquitously in commercial and industrial facilities over the past few decades. A fluorescent lamp operates by exciting mercury vapors within the glass tube to produce ultraviolet (UV) light, which causes the fluorescence of the phosphor coating and thereby generates light in the visible spectrum. The fluorescent lamp requires a ballast to maintain the gas excitation and voltage conditions. Compared to an incandescent lamp, a fluorescent lamp converts substantially more electrical power into useful light, delivers a significantly longer service life, and produces diffused light over a long length for more uniform light distribution.Notwithstanding their advantages over incandescent lamps, fluorescent lamps have a host of problems. With energy cost on the rise, the efficacy of fluorescent lamps cannot keep pace with the ever-changing energy codes and sustainability requirement. Cold weather operation, frequent switching, dimming control, and mercury disposal pose challenges for fluorescent lighting. What's worse than these issues is that fluorescent lighting substantially deteriorated the quality of light for interior illumination. With fluorescent lighting, flicker becomes a problem because low cost ballasts usually fail to deliver electrical current with low ripple content. Exposure to light flicker can cause eye strain, distorted vision, headaches, and even trigger ailments as serious as epileptic seizures in some photosensitive populations. The high efficacy of fluorescent lighting is achieved partially by increasing the percentage of high energy short wavelength light in the spectrum. Imbalanced wavelength distribution across the visible light spectrum results in light with a cool white appearance and low color rendering performance. Fluorescent lighting makes broad-spectrum white light that renders color naturally a luxury. The short wavelength light in the blue region of the spectrum is known as biologically effective light. Ill-timed exposure to an excessively high dosage of blue light may can impair human health and well-being. Prolonged exposure to such high intensity, high energy short wavelength light may also cause photochemical damage of the retina.
The industry is witnessing a rapid migration from fluorescent lighting to solid state lighting based on light emitting diode (LED) technology. An LED is a semiconductor package within which white light is generated through electroluminescence and photoluminescence. Core to the package is an LED die which is basically a forward biased p-n junction device. It comprises an n-type semiconductor layer, a p-type semiconductor layer, and an active layer interposed between two semiconductor layers. When a forward voltage is applied across two oppositely doped layers, electrons from the n-type semiconductor layer drop down from the conduction band and recombine with holes from the valence band of the p-type semiconductor layer in the active region of the diode. Radiative recombination of holes and electrons releases energy in the form of photons with a narrow wavelength distribution. The narrow bandwidth of the emitted light must be broadened to obtain white light of a desired spectral characteristic. The narrow-band emission of shorter wavelength photons (e.g., blue photons) is partially or completely down-converted by a phosphor or a combination of different phosphors to produce electromagnetic radiation that spans a broad range of wavelengths.
Advantages of LED Lighting
LEDs overcome many of the disadvantages of traditional light sources. Apparently, high energy efficiency, long lifespan, excellent controllability, and solid state durability are drivers for the continued interest in LED lighting. The highest luminous efficacy of blue pump LEDs made from indium gallium nitride (InGaN), a direct bandgap semiconductor, has exceeded 200 lm/W, which translates to significantly high energy savings over traditional light sources. The efficiency advantage of LED lighting can be credited to not only the high efficacy of light sources, but also high optical efficiency of LED systems and its ability to optimize energy use through adaptive controls. Unlike conventional light sources that emit light in all directions, the directional nature of LED lighting results in highly controllable optical systems with minimal light loss and spill. The semiconductor nature of LEDs lends excellent on/off/dim controllability to LED shop lights, allowing them to work seamlessly with lighting controls and to be tightly integrated with building automation systems. In addition to low energy consumption, reduced maintenance costs and long relamping cycles also contribute to the ROI advantage for switching to LED lighting.An advantage unknown to many people is that tailoring the spectral characteristics of white light became very convenient with LED technology. The spectral power distribution (SPD) of LEDs can be set to exhibit any color appearance that can help create a visually, psychologically, and physiologically enhancing environment. Unlike fluorescent lighting that has to compromise color rendition or to use a high color temperature to achieve a high luminous efficacy, the energy loss during phosphor down-conversion for high color rendering or low color temperature lighting is insignificant when compared to the high quantum efficiency of LEDs. It's also worth mentioning that LEDs do not produces light outside of the visible spectrum, such as ultraviolet (UV) and infrared (IR) radiation. This means LEDs pose less photobiological hazards than traditional light sources.
Not Every LED Shop Light Is Created Equal
LED lighting is not without its challenges. Many end-users take the long lifespan and high energy efficiency of LED shop lights for granted. While longer life is certainly a key advantage, there are prerequisites. Failure to fulfil these prerequisites may result in the service life of an LED luminaire as short as that of an incandescent lamp. The system efficacy of an LED shop light is the cumulative efficiency of its LEDs, driver and optics. An inefficient LED shop light may have a system efficacy 40% to 70% lower than its light source efficacy.The lifespan and performance of LEDs are interdependent upon forward current regulation and junction temperature control. Excessively high current density or overdriving what the light source is rated for will result in efficiency droop and increased thermal loads. The junction temperature also affect the efficiency of LEDs due to the materials properties in semiconductor packages. With increasing junction temperature, non-radiative recombination and carrier loss in the active region of LED dies increase as well, which results in thermal droop. At elevated junction temperatures, the reduction in the bandgap energy of the active region of the LED die is accompanied by a forward voltage drop across the device. Continuously operating LEDs beyond their maximum rated junction temperature over long periods can accelerate defect growth in the crystal structure of LED dies and materials degradation of package components. This leads to a 30% to 50% decrease in the useful life of LEDs for every 10°C increase in junction temperatures.
LED shop lights are a type of products that finds widespread applications in commercial, industrial and retail lighting. Depending on the operating environment, different sets of performance metrics may be prioritized during the design and engineering of shop lights. In the world of LED lighting, however, the luminaire cost is always in tradeoff with system reliability and light quality. Oftentimes lighting manufacturers cut corners in order to maximize their profits or cost advantages. This causes many LED shop lights to be designed and engineered as low cost commercial-grade products, rather than high-performing industrial-grade products.
Commercial-grade LED shop lights are developed to cater to price-sensitive or uneducated customers. Thus these products can be inadequately designed, under-engineered, and use cheap components. They come with narrow operating windows and are less tolerant to challenging operating environments or long operating hours. Industrial-grade LED shop lights are rugged systems that feature a robust construction and effective thermal management, and use high performance light sources and LED drivers. Despite a high initial cost, industrial-grade LED shop lights offer a significantly higher ROI than commercial-grade counterparts because of their longer service life.
LED Driver
The reliability and efficiency of LED systems are determined by their constitutive components and their reactions upon environmental or operational stresses. An LED shop light is only as good as its driver—the weakest link in an LED system. The role of a driver in LED shop lights is not merely to provide AC-DC power conversion. LED luminaires also come with the need for the driver to provide constant current control, dimming control, interaction with lighting controls, and protection of LED and other downstream components from power surges and other stress conditions. It's essential that the LED driver provides high efficiency power conversion while delivering an output with electrical characteristics matched to the load requirement. LEDs are complex, sophisticated semiconductor devices that have tightly interdependent photometric, electrical and thermal characteristics. Accurate current control regardless of fluctuations in the incoming AC power supply and forward voltage is critical for LEDs to provide high quality lighting and to maintain high performance operation over their rated life.To meet the high efficiency requirements of commercial and industrial lighting applications, LED drivers used in shop lights are designed as switch mode power supply (SMPS) systems. Regardless of topology, an SMPS LED driver utilizes a power switch to control the driving current provided to the LEDs, with the frequency or duty cycle of the switching being adjusted using either pulse-width modulation (PWM) or pulse-frequency modulation (PFM) control. To ensure that the current drawn by the driver is in phase with the line voltage and the total harmonic distortion (THD) is below certain limits, power factor correction (PFC) is required for AC-DC LED drivers with a power rating of greater than 25W. SMPS LED drivers can be divided into two-stage and single-stage circuits. A two-stage circuit includes an active PFC stage sub-circuit followed by a DC/DC converter stage sub-circuit, while a single-stage circuit performs PFC and switching regulation in only one sub-circuit. The single-stage design is intended to reduce the circuit parts count, size and cost. However, single-stage circuits usually do not provide complete ripple suppression, which may result in light flicker. With a switching supply, higher-frequency switching noise can generate electromagnetic interference (EMI) that has to be filtered.
Most premature failures of LED shop lights can be ascribed to LED drivers, which are either underperforming drivers that fail to provide tight load regulation or low reliability drivers that have a lifespan shorter than that of the LEDs. While significant size and cost advantages can be achieved by using barebones circuits with minimal passive components, the output quality may be deteriorated and the LEDs may be exposed to more electrical overstresses. In low cost designs, a high-voltage breakdown path exists through the control circuitry because no galvanic isolation is provided. In this case, extra caution should be exercised during installation and maintenance because touching metal contacts of a luminaire may result in an electric shock. Proper thermal management of the LED driver should be implemented as electrolytic capacitors—an indispensable component of most SMPS drivers—can lose capacitance quickly when exposed to heat.
Thermal Management
Thermal management is an important design consideration as operating LEDs at elevated temperatures can result in color shift, lumen depreciation, and ultimately, reduced service life of LEDs. Most LED shop lights use mid-power LEDs that are vulnerable to high thermal stresses, this makes an effective thermal design an imperative task. Thermal management of LED systems calls for a systems approach that involves the use of LED packages with thermally optimized architectures, driving LEDs with a proper forward current, and designing a thermal transfer path dimensioned to equal the applied power load. The amount of heat that can be removed from the LEDs depends upon ambient temperatures and the design of the thermal path. Ambient temperatures will vary by application, the design of thermal management systems therefore must take in account the real world environments. Abnormally high ambient temperatures are often present in industrial applications. In these operating environments, thermally sensitive components, specifically LEDs and electrolytic capacitors, must be rated for high temperatures.The fundamental part of LED thermal management is to build a high efficiency and high reliability thermal path. A high efficiency thermal path is achieved by maximizing its material thermal conductivity and effective surface area, reducing thermal resistance of the components along the thermal path, and minimizing the length of the thermal path. The thermal transfer rate of the heat sink that provides conduction and convection must outpace the rate at which thermal energy is introduced to the heat sink. It's not uncommon for commercial grade LED shop lights to have an inadequate heatsink design. One of the key reliability determinants of the thermal path is the solder joint between the LED substrate and metal core printed circuit board (MCPCB). Solder joint integrity can often be compromised by thermal cycling, electrical overstresses, and vibration. As such, a reliable thermal path places significant performance demands on the mechanical and thermal fatigue/creep and vibration resistance of solder joints.
Light Source
The quality and performance incorporated in LED shop lights have been patchy. In general, most of these systems, in particularly lamp-based luminaires, use low cost mid-power packages built on the plastic leaded chip carrier (PLCC) platform. In these packages, the LED chip is mounted on a silver-plated metal lead frame surrounded by a highly reflective plastic cavity. This design allows the LEDs to achieve a high light extraction efficiency, resulting in a luminous efficacy considerably higher than other type of LED packages. However, the plastic construction, corrosion-prone silver plating, and vulnerable wire bonding make these LEDs a flash-in-the-pan performer. Under high thermal stresses and drive current, these delicate light sources suffer from accelerated lumen depreciation and color shift. The lifespan of these LEDs depends on thermal and electrical stresses of the operating environment created by the system. When consistent performance over a long operating period is of paramount importance, ceramic-based high power packages or mid-power packages with thermally enhanced EMC housing and Quad Flat No-lead (QFN) anode/cathode pads should take the job.
The spectral characteristics of LEDs dictate the color appearance and color rendering ability of LED shop lights. A light source's color appearance is described via its correlated color temperature (CCT). Most industrial and commercial spaces use cool white light sources with CCT in the range of 4100 K to 5400 K. From a biological perspective this makes sense as light of this color contains an adequate amount of blue wavelengths that support the production of cortisol, dopamine and serotonin in humans for enhanced concentration, vitality, alertness and performance. However, people that had been accustomed to fluorescent lighting prefer an extremely high CCT in the range 6000 K to 6500 K. Simultaneously, lighting manufacturers make every effort to push sales of high CCT products to these uneducated users. This is because the higher the CCT of a light source, the higher the efficacy of the light source.
The white light generation mechanism of blue pump LEDs, the most commonly used white LEDs, involves down-converting part of the short wavelength blue light emitted by the blue LED chip. The shift from high energy, short wavelength blue light to low energy, longer wavelength light is accompanied with Stokes energy loss. Since warm white LEDs require a large portion of blue light to be down-converted within the device package, the Stokes energy loss is considerably high. While high CCT LEDs have a higher efficacy due to low Stokes energy loss, their SPD is saturated in blue wavelengths. Exposure to blue-enriched light at an inappropriate circadian phase can result in circadian disruption and related health and behavioral consequences. Exposure to blue-enriched light in an excessively high dosage will pose a photobiological hazard.
For the same reason, the lighting industry is reluctant to offer LED lighting products with high color rendering performance. The typical color rendering index (CRI) of LED shop lights is 80, whereas incandescent/halogen lamps have a CRI of 97. The SPDs of these products are usually deficient in longer wavelengths that are required for rendering saturated colors. Generally, where color discrimination is important, LEDs with a CRI of 90 or higher should be used.
Lamp-based Luminaire vs. Integrated Luminaires
Lamp-based LED shop lights are similar to fluorescent shop lights in construction but use retrofit LED tubes as the light source. These luminaires are primarily retrofit systems. They are not recommended for new construction projects as the performance and lifespan of these luminaire are far from what people would expect from LED lighting. The majority of the performance from the lamp-based luminaire is derived from the LED tubes, and the luminaire is essentially a holder. LED lamps, such as T8 tubes and A19 bulbs, are retrofit light sources intended for luminaires that were originally designed for incandescent, halogen, and fluorescent luminaires. Their electrical, thermal, and optical characteristics are significantly limited by the physical sizes and shapes of traditional light sources. LED lamps are quickly becoming commodity products. Most of them are low-priced, crappy products that have short lifespans and poor light quality.The LED conversion of fluorescent shop lights comes with the issue of wiring. In retrofitting these fixtures with LED tubes it is important to exercise reasonable care in selecting the appropriate configurations. Depending on the ballast compatibility and driver integration, LED tube lights are available in three configurations: Type A (ballast compatible), Type B (ballast bypass), and Type C (external driver). A Type A LED tube has an integral driver but it is powered the fluorescent ballast. Although no structural modification of the existing fixture is needed, retrofitting fluorescent shop lights with ballast-compatible LED tube lights should consider the lifetime limitation and additional power consumption of ballasts. A Type B LED tube is operated by an integral driver which is powered directly from the main voltage supplied to the fixture. Retrofitting fluorescent shop lights with ballast-bypass LED tubes involves modifications or rewiring to the existing fixtures in order to bypass or remove the ballast. Type B LED tubes perform better and last longer than Type A LED tubes since the removal of ballasts eliminates the failure mechanism and compatibility issue associated with the use of ballasts. Type B LED tubes can be divided into single-ended or double-ended types. Electrical safety during installation is a concern for double-end LED tubes which have power running to both ends. Type C LED tubes also operate from mains voltage but are designed with a remote LED driver. This is the safest retrofit configuration but is also the least used because of the popularity of integrated design for LED lamps.
Integrated LED shop lights use LEDs, rather than LED tubes, as the light source. A holistic approach is employed to ensure the luminaire provides an operating environment matched to the electrical, thermal, and optical characteristics of LEDs. The performance of shop lights is derived from the LEDs in combination with the luminaire's electrical, thermal, and optical systems. Integrated design allows the entire luminaire housing to act as the heat sink which dissipates heat much more efficiently than the inadequately designed heat sink of LED tubes. In contrast to LED tubes that provide a constrained space for the driver circuits, integrated luminaires provide freedom of designing and locating LED drivers. This allows shop lights to be equipped with full-featured LED drivers that provide high performance load regulation and the capability to execute many sub-tasks sequentially or in parallel for increased functionalities and improved reliability. Integrated design facilitates effective control of luminous flux from the light source and thus lends high optical efficiency, uniform light distribution, and enhanced visual comfort to the luminaires. An added benefit of designing LED shop lights as integrated systems is that the luminaires can be designed with a sleek look and clean architectural appearance.
