White Led How to make superbright White LED as bright as possible?
I'm using power supply of 240V AC, going thru a step down transformer to 12V AC, thru a brigde rectifier and across a capacitor. I connect 4 LEDs in series together with a 1K ohm resistor. How to make these LEDs as bright as possible?
If you have a data sheet for your LEDs it would be helpful, while the 20ma value others have given is a reasonable value, if you are looking for maximum brightness you may want to know what your specific LED are rated for, if they are "super bright" the current rating might be higher. You will also need to know the forward voltage at the current you want to use.
Perhaps a typical forward voltage for a white LED might be 3.4V, with 4 in series you have 13.6V, which is more than 12, that might be why some said parallel would be better, but actually you probably have more than 12V, a very lightly loaded bridge rectifier circuit will be charging the filter capacitor to near the peak voltage, not the RMS, 12 * sqrt(2) ≈ 17V subtracting 1.4V for the drop in the bridge, and rounding down since you won't quite get to the peak, lets call the available voltage about 15V
15 - 13.6 = 1.4V; 1.4V / 20ma = 70Ω
Now 1.4V is a pretty small difference, and if your particular LEDs have a little higher voltage, or your transformer or capacitor is small you might not get maximum brightness. So you might put two series pairs in parallel, but each series pair will need it's own series resistor, putting a number of paralleled LEDs in series with one resistor does not work well, since there is some slight variation in LEDs the current will not be equal in all of them (while if they are in series the current has to be same, by definition)
But if you can use a series circuit it will be the most efficient, in the example above, 1.4V * 20mA = 28mW lost, if you used all 4 LEDs in parallel, with a 15 - 3.4 = 11.6V drop needed (580Ω) 11.6 * 4 * 20mA = 928mW loss, not a lot of powers, but still..
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The Rise of Residential LED Lighting and What You Should Know
Almost everyone today knows what an LED light is in the most general sense, but few are aware of how fast it is set to become the main source of general lighting in both homes and businesses. Everyone from the Department of Energy to environmental advocates are pushing the pace of LED general lighting development because of the dramatic savings in energy associated with their use, and the fact that LEDs use no environmentally harmful substances like some older energy-saving bulbs (i.e. compact fluorescents which contain mercury).
Although light emitting diodes have been around since the 1960’s, their use up until several years ago was confined to such things as indicator lights in electronic devices, traffic signals and instrument panels. It wasn’t until the invention of the white LED (in the late 1990’s) that people began to take a closer look at their ability to replace incandescent lighting in homes or businesses. Being a technology that uses a semiconductor to produce light means that the output and efficiency of LED lights is improving at a rapid pace; today’s LED replacements can achieve a life span of 50,000 hours while consuming 80% less energy than a standard incandescent bulb. LEDs that produce a warm white light were invented by accident in 2005 but will allow a person to replace their incandescent bulbs with a similar color light to what they’re used to. An additional benefit of LED lighting is that only a very small amount of UV or IR radiation is emitted, making it highly useful for locations where valuable art is hung on the wall or fading may be an issue.
The current market is full of LED replacement bulbs and lighting solutions, but it is also buyer beware. There is a lot of junk on the market today that if bought and tried will surely disappoint you. Well made LED replacement bulbs are still pricey and the cheap products on the market today, a lot of them being sold through big box stores, will not last nor produce or sustain a bright enough light. On a side note, LED bulbs (LEDs don’t really need to be a bulb!) don’t usually “burn out,” instead their usable life is measured by a certain percentage decrease in brightness. The Department of Energy is using considerable resources to promote LED lighting (also called SSL, or Solid State Lighting) and just recently announced the Energy Star specifications for residential LED usage. That means in the near future you will have some assurance as a buyer that the product you are purchasing really will live up to your expectations.
In the meantime, it is important to buy your LED lighting from a trustworthy source with good customer service in case of any problems you might experience with this new technology. Companies that have established their credibility by working closely with, and traveling to, the factories making the LED lighting they carry are a good place to start your shopping. Look for the offer of a money-back guarantee if you are unsure of what you are buying and how it’s going to work. Now is the time to start using LED lighting, but be sure to shop wisely and you will save yourself both time and money in the long run.
About the Author
Sean Coppom is an employee at Polar-Ray, a Boulder, CO web-based business specializing in LED lighting solutions for residential and commercial customers.
Article by at 2010-04-21 07:04:07
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