Archive for December, 2010

Tips To Think About Before Buying Christmas Lights

24 Dec

LED Christmas lights are popular during the Christmas season because it gives life to our Christmas decors. They come in different kinds and prices. So listed below are a few suggestions in buying the best possible Christmas lights for your home at a reasonable price.

Compute the area where the LED Christmas lights will likely be used.

You must measure the exact length of the area where you’ll put the lights then add a couple of inches based on where your power outlet is located. So if you are planning to hang them outside your home, determine the length of your own home and the distance to the power outlet.

However, in case you plan to put the LED Christmas lights on your Christmas tree, you could use a tape measure to determine the exact length of the Christmas lights that you will need to purchase.
Find out how many strands of Christmas lights you need.

This will depend on your measurements of the area needed to be covered with Christmas lights and length of strands of Christmas lights you will purchase. For example, your measurement is 50 feet and every strand of Christmas lights measures ten feet, then you have to have five strands of Christmas lights.

Additionally it is advisable to use shorter strands of Christmas lights so that you could easily change them if one strand gets broken.

Determine the type of Christmas Lights you need.

To easily determine the sort of Christmas lights, you need to know the objective of your Christmas light. Would you be hanging them outside your own home? Are you planning to set up indoor Christmas lights together with your Christmas tree?

As soon as you know your purpose then check out the features of Christmas lights which include bulbs, strand kind and plug style.

- Bulbs: The bulbs may be in different sizes, shapes and color. You have to determine your Christmas holiday theme so that you can choose Christmas lights that match your other decors. Then, decide on the number of bulbs you like because Christmas lights differ in the number of bulbs per strand. Look inside the package and you would see the number of bulbs included in the Christmas lights.

You also have to check the wattage of every bulb because the illumination of the decoration would depend upon the wattage and number of bulbs you will make use of. Moreover, bulbs have totally different lightning effect. Some bulbs can have a steady glow whereas others blink in different ways. So choose the Christmas lights with the bulb that you will love.

- Strand type: The strand of Christmas lights can either have serial or parallel wires. In a serial wiring, all bulb won’t light up if one of them is busted. So, it’s best to have Christmas lights that has parallel wiring so that even if one of the bulb is broken, all other bulbs would still illuminate.

- Plug style: Select an end to end type of plug if you’re planning to use several strands of Christmas lights. This would permit you to quickly connect all strands of lights together. But if your decorations would only require one strand of Christmas lights, then the plug type will not be that important.

Do a comparison shopping

It’s always highly recommended to do comparison shopping to get the very best deal for your favorite LED Christmas lights. Visit the shopping stores that sell LED Christmas lights in your very own area. You could also watch out for sales on these stores. One other way is doing online shopping.

You can be a sensible buyer for LED Christmas lights by simply complying with these tips. Thus, you can start lighting up your house using your favorite Christmas lights during holiday season.


Light Up Your Home On A Budget This Season With Christmas LED Lights

24 Dec

Christmas is one of those times in a year, when you have to light up your home as brightly as possible. Otherwise, the charm of the occasion is diminished to quite an extent. However, with the plan for extra lighting comes the obvious concern for increased expenditure. This is why, according to a recent research, a lot of American citizens, (around 47% in fact) spend more time planning on how to streamline the expenses on Christmas lighting, than they do for planning which gifts they should purchase. Isn’t it time you tossed all those worries aside, especially when you have an easy solution at your fingertips?

Which solution would that be? Will it involve using fewer lights?

Heavens, no! In fact, you should use even more lights in your home and garden this Christmas than you have ever done before. All you have to do is to switch to a different type of light, and you will be able to cut down on expenditure to a great extent. Stock up on Christmas LED lights right now, to brighten up your home to your heart’s content, without burning a giant hole in your wallet.

What are Christmas LED lights?

These are LED lights that have been especially designed for use during Christmas. Available in a variety of shapes and sizes, not to mention a kaleidoscope’s worth of colors as well, these can match your home dcor perfectly. The lights are powered by indoor transformers and consume less than 40% of the electricity consumed by conventional alternatives, and glow brighter to boot.

That’s not all. These LEDs also last for extended periods of time, which provides the opportunity for a lot of unconventional applications later on.

For instance, how about putting a table lamp in your kid’s room, with a bunch of these LEDs wrapped around the lampshade? Aside from looking really attractive, this could double up as an excellent night light as well.

How much do these cost?

The price of Christmas LED lights is at par with conventional options. Besides, these LED-based solutions last much longer as well, which is guaranteed to provide excellent value for your hard earned cash.


Basic Knowledge about Different Kinds of LED Power Supplies

01 Dec

Although LED’s power saving efficiency is higher than ordinary light sources, it can not be connected directly to public grid voltage like those ordinary ones. It should be configured with special voltage switching device which can supply it with rated voltage and current, providing a sound condition for it to function in normally. That is the so-called special power supply for LED.

However, LED power supplies with different specifications hold different performance and different switching efficiency. In order to fully bring into play the high efficiency of LED, it is important to choose a proper, high efficiency special power supply for each distinct LED. Low efficiency LED power supplies consume large amount of power supply, which will influence the energy saving trait of LED. Anyhow, the stability, power saving trait and the life-span of LED largely depends on choosing a proper LED power supply.

Different types of LED power supplies

Ⅰ. LED power supply can be classified into two types according to driving modes:

A. Constant current power supply

a. Constant current driving circuit is ideal to drive LED, except for its little bit high cost.

b. Constant current circuit can load short-circuit, but it is forbidden to load fully open circuit.

c. The output current in the constant current driving circuit is constant; however, the output DC voltage changes within a certain range according to different load resistance values.

d. The total amount of LED used in one circuit should be limited, because LED has its maximum current and voltage value restriction.

B. Stabilized voltage power supply

a. After setting each parameter in the stabilized voltage circuit, the output voltage is settled, whereas the output current is variational according to the loading.

b. Stabilized voltage circuit can load open circuit, but it is forbidden to load short-circuit.

c. The luminance of the LED will be influenced by the change of voltage after rectification.

d. Proper resistance should be configured in each series of circuit so that LEDs in stabilized voltage circuit will have uniform luminance.

Ⅱ. LED power supply can be classified into six types according to the structure of the circuit:

a. Conventional transformer step-down
Although the size of this kind of power supply is very small, it is a bit heavy and the efficiency is very low, at about 45%~60%. Also its reliability is not high, so it is seldom used.

b. Electronic transformer step-down
The disadvantages of this kind of power supply is its low switching efficiency, narrow voltage range (about 180~240V) and its strong ripple interference.

c. Capacitance step-down
This kind of LED power supply can easily be influenced by the grid voltage fluctuation and the efficiency is very low. It is inadvisable to use it in flashing LEDs because the charge and discharge process in the capacitance step-down circuit will causing extremely large instant current flow, which can easily damage the chip in the flashing LEDs.

d. Resistance step-down
The power supply efficiency in this kind of circuit as well as its reliability is very low. The circuit is interfered by the grid voltage fluctuation, so it is difficult for the power supply to stabilize its voltage. Large power consumption is another disadvantage for this resistance step-down power supply.

e. RCC step-down switching power supply
Advantages: wide range of stabilized voltage; high power supply efficiency (at about 70%~80%). So it is widely used.
Disadvantages: difficult to control the switching frequency; large ripple coefficient of the load voltage; weak loading adaptability in abnormal condition.

f. PWM control switching power supply
At present, the PWM control switching power supply is much more ideal than other kinds of power supplies. Its output voltage and current are very stable, and the efficiency can reach as high as 80%~90%. This kind of LED power supply is made up of four parts: input rectification filter; output rectification filter; PWM voltage stabilizing control unit; power switching unit. High reliability is another advantage for this power supply because the circuit is well protected.


The Application of Infrared LED

01 Dec

Common infrared LED that emits infrared rays has the same appearance with visible light LED. Its appropriate operating voltage is around 1.4v and the current is generally smaller than 20mA. Current limiting resistances are usually connected in series in the infrared LED circuits to adjust the voltages, helping the LEDs to be adapted to different operating voltages.

When using infrared rays to control correspondent unit, the controlling distance is in direct ratio with the emitting power. In order to lengthen its controlling distance, infrared LED should be operated under pulse state as the effective transmitting distance of the pulsed light (modulated light) is in proportion with the wind-induced current of the pulses. Thus, by increasing the peak value (Ip) of the pulses, the emitting distance of the infrared LED can also be lengthened. One way to increase Ip is to diminish the duty ratio of the pulse; that is to reduce the width of the pulse (T). The duty ratios of the working pulses for some color TV’s infrared remote controllers are around 1/3-1/4; and for some other electronic products, the duty ratios of the infrared remote controllers can even be as small as 1/10. Through reducing the duty ratio of the pulses, the emitting distance for small power infrared LED can also be increased in a large extent. Ordinary infrared LEDs can be divided into the following three types: small power one (1mW-10mW), medium power LED (10mW-50mW) and large power LED (50mW-100mW and above). The modulated light can be generated by adding pulse voltage with specific frequency on the driving diode.

The controller with infrared LED can emit infrared rays to take control of correspondent unit, and at the controlled unit end, there is also a receiving device to turn the infrared light into electricity, such as infrared light receiving diode, photoelectric triode and so on. Emitting and receiving matched infrared diode has also been applied in practical use.

There are two emitting-receiving modes for infrared LED and the controlled unit, one is direct light emitting mode, and the other is reflecting light mode. In the direct light emitting mode, the emitting diode and the receiving diode are installed in the emitting end and the controlled unit end respectively, with a certain distance between them. As to the reflecting light mode, the lighting diode and the receiving diode are in parallel. Only when the infrared rays emitted by the diode were reflected by something can the receiving diode get the infrared rays, thereby stimulate the controlled unit to operate. Besides, infrared emitting circuit with double diodes bears higher power and longer functional distance.

Infrared LED chips with different wavelengths can be applied in extensive devices, for example:

1. Infrared LED chip with wavelength of 940nm: suitable to be used in remote controller, such as remote controllers for household appliances.

2. 808nm: suitable to be used in medical treatment appliances, space optical communication, infrared illumination and the pumping sources of the solid-state lasers.

3. 830nm: suitable to be used in the automated card reader system in freeway.

4. 840nm: suitable to be used in colored zoom infrared waterproof video camera.

5. 850nm: suitable to be used in video cameras that are applied in digital photography, monitoring system, door phone, theftproof alarm and so on.

6. 870nm: suitable to be used in video cameras in marketplace and crossroad.


How to Choose LED Driver IC

01 Dec

LED has established its unshakable position in the backlighting of portable devices. Even in the backlighting for the large-sized LCD panel, it has started to challenge the mainstream CCFL. In lighting, LED is especially popular in the market due to its highlighted features like energy-efficiency, environmental friendliness, long lifetime, and low maintenance. The driver circuit is a crucial and integral part of the LED. Whether in lighting, backlighting or the display panel, the choice of the technical architecture of the driver circuit must correspond to specific applications.

The LED lighting mechanism goes as follows: when the forward voltage is applied to both ends, the minority carrier and majority carrier in the semiconductor recombine to release surplus energy, giving off photons. The main functions of the LED drive circuit are to transfer the AC voltage into a constant power supply and match the voltage and current according to the requirements of LED devices. Apart from safety need, the LED driver circuit must also include two other basic features:

First, a constant current should be kept as long as it is possible, thus the output current variation is able to be maintained between the range of ±10% especially when the power supply change goes beyond ±15%range. Here are the reasons for having a constant current driver when using LED as the monitor, other lighting devices or backlighting:

1.To prevent the drive current from exceeding the maximum rate and further affecting its reliability.

2.To meet expected brilliance requirements and ensure the color and brilliance homogeneity of each LED.

Second, the driver circuit should keep low power consumption so that the LED system efficiency can remain at a high level.

PWM (Pulse Width Modification) is a traditional light adjusting technology, which uses simple digital pulses to switch on and off LED driver from time to time. The system only needs to supply wide and narrow digital pulses in order to easily change the output for adjusting LED brilliance. The advantage is that the technology is able to provide high quality white light with high efficiency through easy application. But there is a fatal disadvantage: it is susceptible to EMI (electromagnetic interference), sometimes even produces audible noises.

Voltage boost is an important task of the LED driver circuit, divided into two different topological modes, namely, voltage boost via the inductor and charge bump. As the LED is current-driven, and the inductor is most efficient at the moment of current transfer, so the greatest strength of voltage boost via inductor lies in the high efficiency, which can reach 90% if properly designed. However, its weakness is as much remarkable, i.e., strong EMI, which imposes high requirements on systems of telecommunication products such as mobile phones. With the appearance of charge pumps, most mobiles don’t boost voltage via the inductor. Of course, the efficiency of voltage boost via the charge pump is lower than that in the other way.

No matter in lighting or backlighting applications, the product designer has to face the problem of raising the driver transfer efficiency. To improve the transfer efficiency is not only beneficial for portable products to extend standby time but is also an important means to solve the LED thermal dissipation problem. In lighting, the use of the high power LED also underlines the problem of enhancing the transfer efficiency.

LED needs current and voltage stabilizing components at work, which should be featured with high divided voltage and low power consumption, otherwise, the highly efficient LED will lower the overall system efficiency because of high working consumption, contradicting the principle of energy-saving and high efficiency. Therefore, the main current limiting circuit should use highly efficient circuits like the capacitance, inductor or switching circuit with power supply as it is possible to ensure the high efficiency of the LED system instead of the resistor or the series voltage stabilizing circuit. The series constant power output circuit can keep the LED light output constant in a wide range of power supply, but normal IC circuits will lose some efficiency. The adoption of switching circuit with power supply is able to guarantee constant power output with high transfer efficiency under dramatic voltage variation of the power supply.

At present, LED with its luminous efficacy is far from replacing the three band fluorescent lamps, yet LED lights can efficiently work under safety extra low voltage (SELV), for instances, underwater lights in swimming pools or paddling pools, mining lamps. Besides, LED has unique advantages in the direct use of green energy like solar energy, wind energy, or emergency lights. Particularly in light adjusting, LED cannot only realize zero to one hundred percent adjusting, but also maintain high efficacy during the whole adjusting process without hurting the durability, which is a difficult task for gas discharge lights.

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