LED-based lighting is still far from mainstream technology, and its design is constantly changing. Consumers have not yet indicated that they will open their wallets and the cost-effectiveness of their houses, and companies are unwilling to spend money in the current economic environment. Nevertheless, early SSL (Solid State Lighting) products are entering store shelves and inventory. These initial designs can indicate the direction the SSL design will take, at least in its early stages.
This article describes the disassembly of five LED lighting products to understand their performance and the components and design topologies they use. It is possible to abstractly design or speculate on the most effective way to use new technologies. However, the designers and manufacturers of these products have made many assumptions about component pricing and availability, manufacturing and distribution pricing, features required by potential customers, and prices that the market will bear. This level of uncertainty is common when manufacturers introduce technology. In five years, you will know what the market wants and are willing to pay for efficient lighting, but no one knows now, partly because there are so many unidentified variables. Where will energy prices go? Will the government formulate an energy policy and stick to it? Will global energy demand affect investment in energy-efficient hardware?
Considering all the unknown factors facing the introduction of SSL products, it is really surprising that companies and investors have the courage to invest. It is the engineer's responsibility to use the available components to make the best design based on the price point set by the marketer. Therefore, it is very interesting and even exciting to look inside these products and understand the thinking of engineers and marketers.
The dismantling journey started at 48 inches. LED T8 size downlight. You can't call it a "replacement" T8 lamp because it will not enter the fixture of the fluorescent tube. Fluorescent tube lighting requires lamps with ballasts, which is the term used in the lighting industry to close the power supply to the lamps of the light source. This arrangement is suitable for technologies where the light source wears out before the power control circuit on average. Fluorescent lamps apply voltage to a glass tube containing vaporized mercury. The excited mercury emits photons of ultraviolet wavelength; these photons hit the phosphor coating inside the tube, which in turn emits light of visible wavelength. The high-quality T8 fluorescent lamp has a luminous efficiency of 100 lumens/watt or higher.
It is impractical to directly replace fluorescent tubes with LED tubes because the power requirements of the two types of lamps are different. Most currently available LED tubes contain their own AC/DC power supply. In contrast, fluorescent light fixtures contain power conversion ballasts.
Figure 1 shows the LED T8 tube light from Alpine Electronics. Alpine also offers an improved fluorescent lamp unit without a ballast. Each 18W tube emits 820 lumens, which is equivalent to nearly 46 lumens per watt, which is about half of that emitted by high-quality fluorescent tubes. Figure 2 shows that each tube contains three rows of 96 LEDs. When the tube lights up, the middle row of LEDs is warmer yellow-white (Figure 3). The end cap routes the AC power to the internal power supply of the tube (Figure 4). The aluminum back is a thin circular cover that only touches the LED PCB (printed circuit board) at the edge, which does not provide much heat dissipation. The PCB does not have a metal core; it looks like a garden-style fiberglass board. Therefore, the circuit board itself is not a heat sink. Figure 5 shows the power supply. The part number on the three-terminal power conditioner is missing, so there is no part information. However, this part contains a large number of electrolytic capacitors (Figure 6). Two PCBs bound together form a 4-foot-long lamp. Figure 7 shows the staples connecting the two boards, and Figure 8 shows the top view of the staples and jumpers connected to the power bus.
The lamp specifications state that the lamp has a lifespan of 50,000 hours; however, for all these electrolytic capacitors, this number seems doubtful. Using electrolytic capacitors can get a life of 50,000 hours, but I think the manufacturer may have just selected the general lifespan number of the LED component and used that number for the entire lamp. The internal structure of the tube reflects excellent manufacturing quality-much better than many other LED lamps and CFL (compact fluorescent lamps).
The LEDs are located in a matrix of 288 diodes in 18 parallel strings, with 16 diodes in each string. The voltage drop of each LED is about 3.2V, and the total voltage of the entire array is about 50V. The specification states that the lamp is 18W, so each string consumes about 1W, which means that each diode uses about 0.0625W. This number is far from the HB (high-brightness) LEDs you usually encounter when designing LED lighting, which uses about 0.5 to 1W of power.
The power supply obviously outputs 51V dc—that is, although it measures 51V dc on the load, it may be a constant current rather than a regulated power supply. In any case, all the diode strings are connected in parallel at the output of the power supply-this is not an ideal load for the LED matrix, because as the LEDs age, their current curve will change. In the array shown in Figure 9, the string with the lowest resistance draws the most current, which heats the diode and produces a difference in LED output. One of the most important characteristics of a light source is uniform and consistent intensity and color; a matrix like the one in the picture requires hot spots. A better option is to use a constant current driver for each string (Figure 10).
Many power management IC suppliers have developed their own LED driver chips, such as Texas Instruments (TI)'s C2000 DSP-based IC driver, which is very suitable for applications with multiple strings. National Semiconductor, International Rectifier, Marvell, NXP, NEC, On Semiconductor and several other companies also provide LED driver chips, but the C2000 uses a DSP core with multiple PWM (pulse width modulation) outputs; one chip can provide up to seven A LED string provides a constant current source.
You might think that 18 strings require 18 control loops. For tube lamps with limited cost, this requirement will be a problem. Why not give up those slim 0.0625W LEDs and use some high-brightness LEDs with 0.5W each output? Then you only need to use 36 HB LEDs. However, this approach brings some other limitations. For example, 0.5W HB LED provides a unique strong point light source, and neither lighting designers nor consumers want this type of lighting. In addition, HB LEDs of this power also have heat dissipation problems: 288 0.0625W LEDs dissipate heat more evenly, and inexpensive PCBs can be used. However, the use of fewer high-power LEDs requires a heat-dissipating substrate and may require the use of a heat sink, thereby increasing the price of the tube lamp.
This design uses fewer expensive LEDs, power management equipment, and strong point light sources, but due to uneven LED aging, which will affect light quality and reliability, its current source is uneven. The challenge for LED-based T8 LED replacement lamps is to cost-effectively replace today's $2 fluorescent lamps and maintain light quality. The price of Alpine T8 tubes ranges from US$65 (US$1,000) to US$95 (one) per tube.
Although Alpine's tubes compete with fluorescent lamps for $2, Alpine can find customers because when you consider replacement costs (including labor, downtime, and difficulty of access), the longer life of LEDs can prove to be in some hard-to-reach applications Its higher cost is reasonable. Early adopters who value LED color quality and just like to have the latest technology may also be willing to pay a premium.
Since you have to modify the fluorescent lamp installation, you cannot consider the tube lamp as a real substitute for the fluorescent lamp. Home Depot's recently launched EcoSmart dimmable LED bulb is an example of a real replacement for 40W incandescent bulbs (Reference 1). The 8.6W lamp is priced at $20 and comes with a five-year warranty. The light provides warm diffuse light; it dims well; and it does not produce noticeable audio noise. As shown in Figure 11, it has a glass dome-shaped housing that covers the LED and is not easy to separate. LEDs are not the common strong light sources you see in other LED lights, such as the non-dimmable 7.5W bulb from TESS (Topco Energy Saving System), which I disassembled in March (Reference 2 and Figure 12). According to the specifications on the package, the lamp uses seven LEDs with an output of 560 lumens. These large surface area LEDs provide a pleasant diffuse light source, only two of which output 429 lumens at 8.6W.
Figure 13 shows a close-up of the EcoSmart LED: I removed one to find the manufacturer's label or mark, because officials from LSG (Lighting Science Group), the designer of the bulb, did not want to reveal the company's supplier. I can’t find the manufacturer’s label, but there is an obvious part number AM6L1, which looks like an LED array, which means that the LED encapsulates several tiny LED chips in one package and covers them with a single phosphor . Using this diffuse light source is a good choice because there is no pixelation.
In order to determine the LED used in the lamp, I carefully read the LED catalog of the Japanese LED manufacturer Citizen (Reference 3). It looks like AM6L1 is similar to Citizen's 6W CCL-L251 LED. In other words, LSG will reduce the rated power of the two LEDs of the bulb, and the operating power of each LED is less than 6W-this is a wise and conservative design choice.
The rubber compound encapsulates the electronic device-this is a good choice for lighting technology because the encapsulation cushions the electronic device from all the vibrations inherent in small, easily accessible bulbs (Figure 14). However, the dismantling is not so good. However, the rubber packaging material can easily fall off, exposing all driving electronics. The most promising IC (ie the IC with the most leads) is the 10-pin MSOP with the mysterious "SULB" mark on the top (Figure 15). A quick Google search revealed that SULB is the "top mark" for National Semiconductor's LM3445 TRIAC (Triode Alternating Current) switch dimmable LED driver (Reference 4). I can only see a 50-μF Nichicon electrolytic capacitor, which works at 105°C. The black capacitor-like component in the picture is an inductor.
The electrolytic capacitor visible in the right part of the figure is a potential weak link. This design uses high-quality components to reduce the risk of failure. Solder joints are the Achilles' heel of the reliability of LED lighting (Reference 5); using the highly integrated LM3445 LED driver can reduce the number of solder joints. Use a small amount of thermal grease to mount the metal substrate of the LED directly on the finned metal heat sink (Figure 16 and 17).
Compare this method with a seven-LED lamp from TESS, where the LED is located on a metal core substrate and then on a flexible thermal interface before mounting on the heat sink. EcoSmart uses a simple method to quickly remove the heat from the LED. The overall design concept improves reliability by reducing the number of components and related solder joints.
These two disassembly are lights that conform to the shape of the lighting. For my next project, I will learn more about the new lighting engine from Cree, a manufacturer of LED components. You can think of the Cree LMR4 module as a light engine that can be used as a building block for lighting fixtures (Figure 18 and Reference 6). You can quickly disassemble this light by removing a few screws. A large white metal cover covers the entire device (Figure 19). The back of the LED unit is on the right side of the penny, and the lampshade is on the top of the unit. The lid has a simple paper cone as a reflector, and a diffuser between it and the transparent plastic lampshade.
Cree's TrueWhite color mixing technology combines discrete white and red LEDs. Other methods to produce a consistent warm white color from LEDs rely on combining multiple color emitters in one LED package or by adjusting phosphors. The TrueWhite implementation of LMR4 has five white LEDs and three red LEDs. When you turn on the lights and gradually turn on the power, the four main white LEDs and the two main red LEDs light up somewhat evenly (Figure 20). When you continue to turn on the power, the second white and the second red will turn on. If you turn it all the way up, the auxiliary white LED will fully light up and match the main white LED in brightness, while the auxiliary red LED does not seem to light up at all.
In addition, if you keep the light at the power level where the 5th white LED was initially turned off, it will light up after a few minutes, which may mean that the color of the LED light changes with temperature, while the other two are balancing the LED color with It varies with temperature and power. Cree's marketing video mentions "active color management" when describing TrueWhite, so power and thermal response must be the active part.
An eight-pin TI 9C L2903 dual differential comparator is located next to the LED. The chip may compare the current through the main LED and turn on the auxiliary color balance LED when the current exceeds the maximum threshold (Reference 5). Figure 21 shows the substrate after ejecting from the bottom plate, showing the metal core. The label "Berg MP A2" on the front looks like a Bergquist Thermal Clad metal core substrate, which contains a circuit layer on the dielectric layer on the base metal layer. The substrate is clamped on the adhesive, thermal and conductive layers of the power substrate (Figure 22). The National Semiconductor LM3445 TRIAC dimming SULB may be a power management IC, and the capacitor is a 22-μF, 200V, 100°C Nichicon device. The power and ground wires pass through a large ferrite bead to filter noise.
Cree stipulates that the power factor of the LMR4 module is greater than 0.80 at 120V ac/60 Hz, or greater than 0.90 at 230V ac/50 Hz. Using the trusted $20 Kill A Watt power meter from P3 International for measurement, the power factor is 0.56. It is true that Kill A Watt is not the most advanced power meter, but 0.56 is far from 0.8. Removing the Lutron dimmer from the circuit will cause the module to work directly under AC line voltage, increasing the power factor to 0.91, so even if the switch indicates 100%, the TRIAC dimmer is obviously not fully opened.
The previous dismantling are all production LED lights currently on sale. The next example is the Helieon demo unit from Bridgelux (Figure 23). Bridgelux and Molex teamed up to design a socket and module combination for the new installation (Figure 24).
The Helieon module includes a Bridgelux LED array, lens and socket mounted on an aluminum spreader. The LED array can provide 500 to 1500 lumens in 3000K warm white or 4100K neutral white, and the optics of the module shape the light path to provide narrow, medium or wide flood angles. You can change the color temperature and beam focus of the white light unit by replacing the LED module. The socket connects the LED module to the ceiling or wall and supplies power to the lamps. Helieon lacks the heat sink required for a fully functional lamp; I suspect that this omission is due to its momentary switch: preventing the evaluator from opening and leaving the evaluation kit, causing overheating.
The Helieon design also lacks power management circuitry, but it is another example of an LED emitter for LED lighting. Bridgelux LED encapsulates the LED emitter matrix into an LED device. This method is similar to the method used by Citizen LED in EcoSmart bulbs, but on a larger scale. Bridgelux devices provide up to 1500 lumens in this package (Figure 25).
Bridgelux aims to provide a demonstration unit for designers who want to evaluate the Helieon LED module and socket combination; the power management circuit is only used to demonstrate the Helieon module. Nevertheless, it shows that the power management of the LED is not trivial. The device will make a ticking sound whenever you insert a brick, and it will make a humming sound when you press and hold the momentary power switch. The dimmer circuit does not use TRIAC and only dims the light by about 50% instead of almost turning it off. "Power management is the bane of my existence," said Jason Posselt, Bridgelux's vice president of sales, who commented on these unwelcome features and may have expressed the thoughts of many other LED manufacturers.
I can express the required price-performance ratio! I used to pay $0.28 for each 40./60/100W bulb (awarded 20 years ago, but even doubled...) to buy a bulb that lasts an average of 1000 hours. It produces pleasant light that enters any
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