作者：Blade

Simple and practical home lights are the king

In recent years, driving by the property market, Lighting consumption develop to the energy conservation, overall development of intelligent, professional lighting store, lighting store are rising. Lighting product design shows a variety of personalization trend, crystal home lights, children’s lighting, creative lighting, all kinds of lighting ranging. It is gratifying that, in the pursuit of individuality at the same time, more and more lighting products began to focus on energy efficiency, green lighting concept has been  the unanimous approval of the businesses and consumers.

home lights

Simple lighting is the more popular one

The person in charge of a dealer Miss Yu said, appliance lighting business in 2010 are off season compared to the previous light. She believes that the biggest reason is the decoration people is relatively few. Qingyuan property prices may be inflated, and invest more.” Some people have two or three suites, actually, they can not live so much, so mostly they invest.

Secondly, lighting shop are getting more and more, competition is intense lighting design style, type of update soon, a shop can not cover every style, competition is inevitable. “Miss Yu said, as a brand to ensure that business still have certain advantages. Such as after-sales service, factory support.

In another aspects, in the product application, simple is the mainstream of lamps in the market. Miss Yu introduced, “the Op products has  always been a concise, easy to clean and more popular.” The modern lamps are in the “light up” to “pretty up” transition, focusing on the decorative and aesthetic effect of the lamps. Many consumers do not like complicated decorations. “Simple is not simple, but taste, simple lighting can better reflect the taste of home.”

LED lights entered the home lighting

With the popularity of green lighting, energy efficient lighting market is more open. At the same time, consumers can largely accept the energy-saving lamps. “Our energy-saving lamps sold well, consumers are aware of the benefits of energy-saving lamps. “Miss Yu introduced, in addition to the ordinary energy-saving lamps, LED home lights are gradually getting popular. If the 2009 is LED landing home lighting “signs of the Year, 2010” Try the year, so 2011 is likely to enter the year.

How far does the gap between reality LED lighting market and the ideal one?

Incandescent will be eliminated, and energy-saving lamps are emerging, LED lights are in the ascendant, but the industry on the LED lighting market prospects and rashness. It is based on LED prospects promising, from the international semiconductor giants to unknown small factory. Some insiders jokes that now is not involved in LED ashamed speaking of the lighting industry.

LED lighting market

However, the industry’s lighting market outlook is very rashness, more concentrated in low-end market, a conservative estimate of 3 yuan of each incandescent lamp. The world’s 2 billion stock market, but six billion; 10 billion energy-saving lamps of 20 yuan but 200 billion, while the high-end intelligent LED lighting market, the report estimated that the capacity will reach $ 200 billion in five years.

The data show that the lighting energy consumption accounted for 22 percent of the world total electricity consumption is green lighting. The significance of 80% power consumption can be reduced from incandescent to energy-saving lamps. When the replacement completed, the global LED lighting market energy consumption will be reduced according to 17% of current NXP chip used in energy-saving lamps of 60 million, equivalent to an annual reduction of 500 million kilograms of carbon dioxide, and future sales is expected to expand 10 times and 20 times, saving significance is enormous. Criticized by the world energy-saving lamps mercury pollution, in fact, there is a great misunderstanding. On the other hand, energy-saving lamps mercury contamination does exist. However, many natural areas have mercury pollution, the relative energy-saving lamps talk about mercury discoloration. Study have shown that the mercury in a energy-saving lamps are less than a marine fish such as salmon sharks.

Right now, International semiconductor giants basically has embarked on the LED layout, NXP already has a chip by 70 005 thousand hours, 105-degree heat of the experimental test, which is the world’s first application-level LED chips, and its SSL2101/2102 since 2009since May, has sold 10 million in May this year, sales momentum, Jin Meng, more than dozens of well-known companies have for dimmable LED bulbs. Which SSL2102 International Lighting Fair in Las Vegas in May 2010 Technology Innovation Award.

For the heat problems that LED lamps designed. Although there has the fan, open and  short-term solution, yes solving the fundamental direction of the LED application is to improve the light efficiency of the same upgrade. LED is also a semiconductor, subjecting to Moore’s Law. The performance will be greatly improved on a regular basis. Talking about the LED market applications, some people think that the direction should be intelligent, innovative lighting.

Cooling design of high-power LED tunnel lights

LED is a type of photoelectric devices. Take the existing most advanced high-power LED chips for instance, the conversion from electrical energy to optical energy is only 15%-20%, far less than the requirements of most industrial applications and commercial applications. The rest 85%-80% energy will be transformed into heat, keeping LEDs in an over-heated state. That is the reason why most high-power LED lighting products have relatively short service lives. On the other hands, the luminous flux (lumen output) of LED lights will be reduced with the increase of PN junction temperatures. Thus an incompetent cooling design may dramatically cut down the lighting effect and working time of high-power LED tunnel lights.

 

Thus an incompetent cooling design may dramatically cut down the lighting effect and working time of high-power LED tunnel lights.

 

Currently, there are three major solutions for cooling technology of high-power LED tunnel lights: 1) natural cooling. Adding fans/ventilators and heat pipes/sinks to assist cooling. Natural heat dissipation is base on natural convection and thermal radiation, reliable structure, waterproof, but strict in the structure design, cannot be easily handled. Normally, the practical effects are far less than the theoretical results. 2) Mandatory cooling through fans/ventilators on the base of forced convection. This method can provide a much faster cooling effect, but generate more noise and cost a lot, hard for waterproof. 3) Mandatory cooling through heat pipes/sinks. This technology takes the use of heat pipes to conduct unwanted thermal energy to heat sinks/pins to realize a rapid thermal dissipation. There are no other motion compartments and the entire system is more stable, but correspondingly cost a lot.

 

Different from ordinary roads, tunnels have many special properties. Mandatory cooling with the help of heat pipes and heat sinks would be the most suitable cooling technology for high-power LED tunnel lights among three. The vertical design of heat dissipation channel can realize the modularization of cooling section. Normally, high-power LED lamps using this cooling method can maintain a working temperature below 70℃, keeping LED chips working in a stable low-light-attenuation state, improving the maintenance factor to save more maintenance costs.

 

According to the airflow characteristics within tunnels, scientists usually made asymmetry ventilation designs, ensuring the air convection cooling. Meanwhile these asymmetry designs also can reduce the mass of soot and other pollutions generated by vehicles to enter the cooling chamber. These dusts may probably absorbed by cooling devices and reduce heat dissipation effects.

Global emerging markets in all lighting are very active

Since 2008, the U.S. and European markets influenced by the financial crisis, so the demand decreased. The importance of global emerging markets are also increasingly subject to the attention of manufacturers: South America and South Africa in recent years. The rapid development of the Middle East market has large demand for low-priced products. In addition, Russia and Eastern Europe is also a potentially large market, many companies have also demonstrated the interest of Russian and Eastern European markets.

Global emerging markets in all lighting are very active

Indian market, India is 80% all lighting products imported from China in the Indian market, the LED lights outdoor use huge space, while the Indian Government is considering the traditional lighting systems for environmental protection and energy saving LED lighting system, which is expected to LED lighting market in India. The growth rate will reach 41.5 percent, and continued until 2015. In South America, Neo-Neon since last year already and gradually increase to expand efforts to develop LED lighting market in South America, led by Brazil. The first LED tunnel light project in the city of Sao Paulo, Brazil’s central city of Neo-Neon Group’s Silver Rain Lighting do the tunnel Ayrton Senna throughout South America’s first highway LED tunnel lighting, which is the landmark projects for LED lighting applications in the tunnel and highway.

In the South African market, there are Chinese enterprises active figure. Zhang Qingyu, NVC lighting Vice president, said that South Africa has become one of the NVC sales overseas markets. In South Africa, NVC dealer business model matures. Right now, the key distribution channels, specialty channels, modern supermarket channels.

Take the Middle East as an example, UAE and other Gulf countries are in a period of economic prosperity, retail, trade and real estate development has led to demand for all lighting, and other areas of Dubai and the UAE population growth has also led to development of the lighting industry.

In Russia, the Kremlin theater lighting project is one of the Shenzhen Mason representative to participate in the global market competition. This prestigious Ballet Theatre “Swan Lake” by Russian Prime Minister Vladimir Putin personally wrote an inscription, called the world”s most elegant theater one. Party on the theater scene design requirements are very harsh. And layers of rigorous testing and screening, Mason eventually stand out from the many international brands.

White Ray will become the mainstream of architectural LED lighting industry in 2013

It is estimated that the compound annual growth of LED lights industry in Europe is around 38% in next five years, which is the second fastest growing mature market after Japan. Topping the lists were architectural LED lighting (45.8%) and commercial LED lighting (39.2%) due to the price-carelessness and quality-chasing of customers in these two fields.

 

 

White Ray will become the mainstream of architectural LED lighting industry in 2013

 

It is showed by European LED lighting market research report (2011-2015) that the total size of the global architectural LED lighting market is about 3.191 billion USD, accounting for approximately 29% of the overall LED lighting market. Europe, as the prime market, will occupy more than 35% of the global LED lighting market, with an estimated market size of 1.12 billion USD.

 

The multi-color property of LED chips made most business organizations in Europe more willing to spend money on colorful lighting design to promote the cultural and tourism value to attract more visitors.

 

In the past, RGB lighting products were the mainstream in outdoor landscape lighting and indoor decorations. Not until 2011, LED demands were far exceeded by supplies, making the ASP of high-power White Ray LED lighting products dropped by 35-40%. Architectural LED lighting manufacturers started to use White Ray LED lamps. With the rapid improvement of White Ray lighting efficiency and the sharply dropping of prices, it is estimated that by 2013, White Ray will take place of RGB/Color become the mainstream among architectural lighting applications.

 

According to the recent research results, our country has six giant production bases for architectural LED lighting currently. In the first half of 2011, China has put more than 30 billion yuan in LED lighting industry, in which architectural lighting took up 30%.

 

However, the rapid growing trend also brought in disadvantages: the “vicious competition” between companies will weaken the digestion capacity of the market, or even worse, destroy the new-built confidence of this emerging market. Customers’ trust can be easily seriously injured by low-quality products. Once failed to obtain sufficient recognition from market, it is very easily for a new-born industry to be at a virtual standstill for many years. Experts suggested that, before developing architectural LED lighting, government and giant LED enterprises should and are responsible to establish a uniform standard to keep from a potential market chaos.

Three major development potential of LED dimming technology

Dimming is a commonly used technology in the lighting industry. For filament lamps, dimming technology can be easily realized on them in the case of low production costs. While LED dimming technology is much more difficult. For architects and ordinary families, they have no willing to lose the dimming function in the process of replacing traditional lamps with LED lighting products. In this article, we will give a small talk on LED dimming technology to provide some helpful information for someone needed them.

 

In this article, we will give a small talk on LED dimming technology to provide some helpful information for someone needed them.

 

Power Factor (PF) is a rather important parameter among electrical appliances. A higher PF can effectively reduce the energy consumption of distribution network. Thus regulatory agencies around the world are striving to restrict the PF of their electrical appliances within a reasonable region. Energy Star Solid-state Lighting Efficiency Certificate is one famous example, in which the PF of residential electrical applications should be larger than 0.7 and the PF of commercial applications should be larger than 0.9.

 

There are three major methods for LED dimming technology. All of them realize the dimming function through changes of LED drives current. They also can be divided into simulated dimming and PWM dimming on the base of different circuit systems.

 

1)       Dimming LED lights by modulating the derive current. Brightness of LED chips is proportional with the LED drive current, therefore it is available for us to dim LED lights by varying the input current.

2)       Pulse Width Modulation (PWM). ① Convert the input current into square waves, increasing its pulse width; ② Adjust the constant lighting time by adjusting the pulse width, realizing the PF control and dimming at the same time. The dimming frequency is about 200Hz – 10KHz. Due to the visual lag of our eyes, flickers cannot be seen by us. PWM are good at improving cooling sections, which is the biggest advantage of it. However, it also has defects: the excessive input pulse may reduce the service life of LED chips. Currently, PWM is the most common method in LED dimming area.

3)       VID (voltage ID) method. The linear increase or decrease of drive current will have less effect on LED chips. This method is a simulation of power-on/power-off state, also named linear dimming method.

Introduction of real 3D LED display technology

3D LED LCD has become a trend. However, in the field of 3D LED display industry, there is still no 3D-related product coming out. Throughout the history of led lights display technology, from single color to full color, from plane to 3D, it is obvious that 3D LED display technology is an inevitable trend an can be realized one day.

 

3D LED LCD has become a trend. However, in the field of 3D LED display industry, there is still no 3D-related product coming out.

 

Currently 3D used polarized light technology, which can be captured by human eyes and reconstructed within visual centers in the brain. It is in fact seen as a fake 3D technology. Fake 3D technology can have very high resolutions, but still have obvious distinguish with actual feelings.

 

Many universities and research institutes in the world are striving to develop real 3D technology. In spite that the current fake 3D technology has already meet the requirements of most commercial and residential demands, but still incompetent in some other crucial area, such like military, medical (surgery and teaching). Real 3D LED display technology cannot be simply replaced.

 

At the moment, there is no high precision, low cost real 3D LED display been around, but the initial prototype has already created in laboratories, using transparent acrylic tube matrix, evenly distributed by LED tube chips. This device can realize the real 3D effect through the variations of LED lighting spot. Designers also faced up with a lot of problems: which method should be used in modulating signals? Once decided, this procedure will become the most expensive within the entire deign. If simply increase the number of transmitting channels, it is rather difficult to realize the full control of signal processing and signal synchronization. A large amount of computing will be inevitable involved. Currently, scientists are trapped in the options between Hierarchical Data Processing and Column Data Processing. The current work may just prove that which way is impassible. The creation of real 3D LED display still need a long time. Works done or doing would be the bridge to the success future.

 

In the near future, customers may have opportunities to view a “real fight” between Bruce Lee and Fearless before our eyes. Viewing from different angle will give our different visual effects, unlike the current fake 3D technology (same visual effect from different viewing angle).

How to solve the cooling problem of soft LED bars?

1)       Circuit design. The commonly used input voltages of LED bars are 12VDC and 24VDC. Circuits worked under 12VDC are generally combinations of three series branches and multiple parallel branches, while circuit under 24VDC are combination of six series branches and multiple parallel branches. Since soft LED bars should be connected in series, the particular length of these bars all depends on the width of the circuit and the also the thickness of the copper foil. For the reason that the maximum current density per unit area is closed related to the cross section area (CSA), we have to take this point into account during the wiring. Otherwise, soft LED bars will work in overheated conditions due to excessive current. It is cleared that LED lighting products are not sustainable in constant high working temperatures. It will cause unrecoverable damages to circuits and meanwhile reduce the service life of LED lights chips.

 

1) Circuit design. The commonly used input voltages of LED bars are 12VDC and 24VDC.

 

2)       Problems in production process. Since LED bars used series-parallel connections, failure of one branch will increase the input voltage in other branches. Under such circumstance, LED grow lights will send out brighter light, but in the meantime, generate more heat. The clearest example is 5050 soft LED bars. Short circuit in any one of the branch of 5050 bars will double the working current in other branches (from 20mA to 40mA). Users may observe an instant and obvious light enhancing and all together sharply increased working temperature. Circuit may probably be burned up with several minutes in server cases. However this fault is relatively obscure than other problems and hardly be discovered. If testing technicians only concern about whether LED chips work (sending out light) but pay no attention on whether LED chips work in a normal state (sending out normal brightness light), branch short circuit would be frequently occurred. That is the reason why most LED bar producers frequently received feedback from customers complained that their products were overheated and over-bright with unknown reasons.

Solutions:

1)       Increase the distance between wires on circuits as much as possible. It is proved that the ideal condition is larger than 0.5mm. Increase the thickness of copper foils without violating the customers’ requests. General thickness should be 1-1.5 OZ.

2)       Avoid short circuit during the patch.

3)       Double check the patch location before switching on.

4)       Performing electrical testing after switching on. Measuring the light intensity gradually.

rgb led light controller and white led

In recent years, the industry began using LED lights to replace CCFL and EL as the LCD backlight (background light for short) compared to CCFL, EL. LED has the following advantages: 1) to make the LCD more realistic colors, LED backlight cho to provide 130% of the NTSC color scale, only 70% of CCFL. Levels expansion of the LCD image chroma saturation, and more realistic; to make the LCD thinner thickness in the 18-inch LCD module, LED backlight thickness is 4mm to 6mm in CCFL 8mm ~ 12nm; 3) long life, up to 50,000 hours; 4) meet the requirements of environmental protection, LED contains no mercury, 5) compared with EL backlight LED backlight does not arise from interference. Therefore, LED backlighting is widely used in PC, TV, car audio, mobile phones, communication devices, personal digital assistant (PDA) and watches, and other fields, it has become the leading products of the LCD backlighting market.

LED market demand in 2002 accounted for about 60% of the total market demand backlight, green, red, blue and white LED LCD backlight, due to price factors, the green LED Habitat mainstream, accounting for 80 of the LED backlight %. Their rated current of 2mA ~ 20mA, the brightness of 600mcd. Due to the higher cost of the white LED is mainly used for color mobile phones and color PDA’s backlighting and automotive instrument lighting.

2 white LED light-emitting mechanism and characteristics

rgb led light controller and white led

 

2.1 light-emitting mechanism

Single-chip white LED tube of CaN Containing InGaN active layer light-emitting diodes, it is mainly there are two light-emitting mechanism: one is the combination of blue LED and yellow phosphorus, the emission of yellow light through the blue and phosphorus mixed to produce white light; another is to produce white light through a combination of UV LED and red, blue, green and phosphorus.

2.2 Features

White LED main characteristics are: the forward voltage drop of 3.5 V; luminous efficiency greater than 20lm / W, better than incandescent bulbs, fluorescent second (601m / W ~~ 100lm / W), in 2004, the luminous efficiency can be increased 60lm / w, close to the fluorescent level, which is used extensively for the lighting market; luminous flux for the 231m; small package size. SMD-type white LED Nichia Corporation in 2003, model NSCW215, it is a side view of SMD white LED, height 0.8/1mm current of 20mA, the brightness of 600mcd. Toyoda Gosei introduced SMD-type white LED current of 20mA, the brightness of 100mcd the luminous efficiency of 4.5 lm / W to 5 lmW size of 3.2 mm × 2.8 mm, Model of TG the white. citizen company Nichia white LED die developed by far the world’s smallest white LED, a thickness of 0.55 mm. Nichia company’s non-SMD white LED size is 11.2mm (width) x 7.2mm (length) x 6mm (H), long life, up to 50,000 hours or more. White LED lighting market is attractive, the world LED manufacturers to step up development of high-power white LED, high power of InGaN LEDs such as Nichia Corporation has developed the power of 1 W ~ 2 W, an existing LED 10 times. University of California, solid state lighting and display center program developed in 2007 at the light efficiency of 200lm / W white LED.

3 white LED driver circuit

White LED is mainly used for color mobile phones and color PDA, a uniform color LCD backlight require three to four or more white LEDs, smart phones may require six or more white LED. The increase in the demand of the white LED. A strong impetus to the growth of the white LED driver market. Tony Armstrong, Linear Technology Power Division product marketing manager, estimates: “2003 mobile phone shipments will be over 400 million of which at least 60% to 70% of color mobile phones, in addition there will be a 1000 color screen PDA , the market will demand “hundreds of millions of white LED driver, white LED forward voltage drop of 3.5 V, when a similar single-cell lithium, and therefore need a boost converter to solve the white LED forward voltage problems. , Boost, there are two solutions: First, the charge pump (switched capacitor), with its advantages of small footprint, low efficiency, National Semiconductor has introduced White LED Driver With this switched-capacitor, the company believes, if the boost converter will drive in the off state leakage current; inductor switch boost its advantages of high efficiency, but the total area occupied. At present, most of the white LED driver manufacturers inductor switch boost, such as the Catalyst company CAT32 white LED driver, it works at a fixed frequency of 1.2MHz, it can enhance the low-voltage battery voltage and automatically adjusts the drive current, up to 4 white LEDs connected in series. The company is developing even more advanced than CAT32 white LED drivers, it can control the current through the MPU, and the integration of passive components, thus saving costs. Linear Technology introduced a white LED driver integrated on-chip Schottky diode, drive circuit requires only two external capacitors, a resistor and an inductor. The general white LED driver integrated MOSFETs.

The white LED panel driver circuit consists of a white LED driver and peripheral circuits (including transistors, diodes, inductors, capacitors and resistors, etc.) composition. Drive white LED requires a constant current source, current is 15mA to 20mA. The brightness of the LED depends on its forward current, so more of the white LED used in tandem, to ensure that each white LED current is flowing through the same. Being compiled set of 4 series white LED need 14V voltage, the voltage boost regulator to enhance the single-cell lithium battery (2.7V to 4.2V) it said operating voltage. And drive on and off of Q1. Ql, L1, D1 and C1 form a boost regulator, so that the voltage across C1 increases. When the voltage exceeds the forward voltage drop of the white LEDs in series and the current started. The white LED current sensing resistor R1 connected in series to form a feedback loop is closed. Make the R1 at both ends of the pressure drop is the smallest you can get high efficiency. The voltage across R1, the SP6682 voltage of 0.3V parameters, allows the driver circuit efficiency of 87%. Typically, commercially available integrated boost regulator as a feedback voltage to 1.24V bandgap reference voltage, will allow the Rl both ends to produce 1.24V voltage drop across the So that the conversion efficiency is reduced by 7%. SP6682 0.3V reference voltage is far lower than 1.24V, while reducing the efficiency of the reference voltage is proportional to. MOSFET has a small on-resistance and high switching speed of these parameters is superior to other integrated switch. The breakdown voltage of the MOSFET will limit the maximum output voltage by regulating the voltage to the drive required for a few white LED system. Enable the regulator to shut down and restart in order to accurately control the brightness of white LED with a PWM signal on the SP6682 start pin 6.

rgb led lighting system and building design

TPS6106X is a perfect white LED lights driver series. It uses synchronous rectification topology, does not require the traditional white drive external connected rectifier diodes, which can save PCB board space. It supports digital dimming signal completion of the operation of the dimming, the dimming signal can maintain a constant high, and stored dimming information, this function can solve the EMI problems in the conventional PWM mode dimming . In addition, only one GPIO pins can be controlled TPS6106X dimming and shutdown, start function, thus saving the CPU GPIO resources. This article will discuss how to use TPS6106X converter digital dimming application design.

Digital dimming light operation

First, follow the instructions to write the software code of the digital dimming signal, the corresponding brightness adjustment signal sent by the CPU in the phone. But to note is that the signal must meet the basic requirements of the time step for each level of brightness enhancement for 1us to 75us “and” levels of brightness weakening step 180us to 300us of. Each level “step” is required between the duration of greater than 1.5us (td) high, separated, in order to distinguish the series.

Working mode of application design

Shutdown chip operating the ILED with EN common endpoints exert a constant “low” to turn off the chip.

(2) digital dimming dimming operation is complete, you need to keep the luminance signal is high, and store the brightness information. Accordance with the manual, asked to join a luminance signal and luminance signal ILED pin into the chip to complete dimming operation, since the luminance signal must remain high. This is because the ILED pin only to maintain the “high”, the digital dimming function will be enabled, dimming information will be saved. Otherwise, if the revocation of the high, the chip will shut off the dimming feature and lost the dimming information, enabling the chip to automatically return to the FB pin voltage value of 0.5V the state, whether ILED what level, FB pin voltage of 0.5V, output current 0.5/Rs. The brightness setting is stored in the chip, when again the operation of the dimming, just enter the new digital luminance signal. Please note: each dimming operation, the need to maintain the luminance signal for high-potential, in order to ensure that the digital dimming feature is “enabled” state.
rgb led lighting system and building designWM dimming

TPS6106X chip also supports PWM dimming operation, but the circuit diagram needs to be done to improve the: ILED direct connection to the Vin side EN pin is directly connected to the PWM signal, the frequency of the PWM signal is not more than 5kHz (marked on the manual is typically 1kHz) and then proceed to pulse width modulation. D = Ton / T, which Ton frequency cycle in the “high” part.

Quick calculation of the power inductor design

Power inductor design is usually plagued by design engineers, following the design method not only applies to the application of TPS6106X, also applies to all series of white drive applications.

The inductance value is usually selected 4.7uH 6.8uH, 10uH, 22uH, can be selected according to the manual of recommended values. Inductor type selected inductor with magnetically shielded to reduce EMI. White drive current is usually relatively small, basic maintenance at 20mA or so, for the design engineer is very easy to overlook the choice of the inductor current, that just any 40 ~ 50mA inductance to meet requirements. In fact, this practice is very dangerous, because it will allow the inductor saturation converter failure, and even lead converter burned. In accordance with the following formula to calculate the minimum inductor current ILmin:

ILmin = (1.5 ~ 2) × Io / (1-D)

Where, D is the duty cycle, D = (Vo-Vin) / Vo,; Vin is equal to a single 4.2V lithium battery voltage typ 3.6V; Vo, the highest output voltage, if the series of four white LED tubes, each just voltage drop of 3.5V, the total pressure drop is equal to 14V, Vo at least 15V.