By Mark Halper
Posting in Design
A panel of experts assembled in Amsterdam shine light on the strengths and weaknesses of LEDs.
So said LED experts and entrepreneurs on a panel discussion at the Cleantech Forum here, noting that mass adoption will not take place until prices fall – they can be €20 in Europe and $40 in the U.S - and until quality stabilizes.
Their views back up the assertion of several readers of this blog who, after an earlier LED story, posted responses from the U.S. reporting that their pricey LED bulbs stopped working after only months – a far cry from the 25 years claimed by manufacturers.
It is the long life and the 80%-to-90% reduction in electricity that make LEDs the “great light hope” in the illumination world. The European Commission has ordered a phase out of inefficient, power-hungry incandescent bulbs by 2012. The EC claims that alternatives including LEDs will save enough energy to power 11 million households a year by 2020, cutting CO2 emissions by 15 million tons annually. That, in turn, reduces consumers’ energy bill.
Vendors like Philips, GE, Osram Sylvania, Cree and others claim that LED bulbs’ super long life combined with their electricity savings gives them a tremendously low cost of ownership compared to traditional lighting.
One problem – no one has yet owned an LED for anywhere near 25 years, as the bulbs only recently became commercially available. And early results show that quality - including longevity - is patchy.
“At the moment, there are good LED products, but at the same time, also bad products,” said Jean-Michel Deswert, technology manager of Laborelec, a research center within French energy company GDF Suez. “It’s difficult for the customer to make a good choice.”
Louis de Fouchier, CEO of French LED distributor and research firm HomeLights S.A, agreed.
“We’re entering a world where you will find on the shelf low, very bad, better (and) higher quality bulbs. And the quality of what you get will depend on the price you’ll be ready to pay,” said de Fouchier, speaking on the Amsterdam panel, organized by San Francisco-based research firm Cleantech Group.
Panelists noted that bulb quality varies widely across all aspects, including brightness, longevity, durability, and the light’s ability to faithfully render an object’s color. As noted in our earlier article from Milan, lighting designers also do not like LED’s relatively cool “color temperature” when compared to the warmth of incandescent bulbs.
But do consumers really want to spend hours wandering through hardware and do-it-yourself stores pouring over the pros and cons of myriad bulb options? “The consumer is confused, and is going to be confused for some time,” said de Fouchier.
Martjin Dekker, CTO of Lemnis Lighting, a Dutch start-up manufacturer of LED bulbs, said failures tend to stem from a breakdown of components within the bulb other than the bulb’s LED (light emitting diode, which is a semiconductor). Those components convert homes’ alternating current to direct current, and knock voltage down from the 220-240 volts and 110 volts common around the world, to around 5-to-12 volts. They also include a heat sink.
Not only can these components fail, but they also explain why LED prices are high. And that, said Dekker, is the leading explanation for the technology’s slow adoption.
“The market for today is still very slow which is a direct consequence of the price,” noted Dekker. “The price is too high for mass adoption.”
Dekker said he is optimistic prices in Europe will decline to consumers’ acceptable levels in the second half of this year, and that other geographic markets would follow in 2012. He did not predict what the price would be. Josh Gould, a Cleantech Group analyst, said LED prices are declining by 20% to 25% per year.
The panelists said that other LED attributes will help usher in the bulb. For instance, LEDs are easier to control remotely than are traditional bulbs, noted Marc Ottolini, CEO of UK lighting control start-up Isotera. That means users can switch them on and off and alter their color as well as their brightness - like never before. That, in turn, will lead to new business models in which buyers purchase lighting services rather than bulbs, panellists said.
Adding to consumers’ hopes that LED prices tumble: many governments around the world - like the EU and its 2012 policy - are phasing out incandescent bulb. If LED prices don’t come down soon, consumers may have little choice other than to pay an unfamiliar sum for the thing they screw into a lamp in the corner of the living room. Let’s hope the engines of innovation knock a few dollars off the upfront burden of buying a bulb for a lifetime.
May 12, 2011
My experience with LEDs has been mixed. I have steadily changed interior lamps to LED as the tungsten and fluorescent units failed and where the LED would supply sufficient illumination. A point to notice here is that the numbers marked on the LED packet are often meaningless - I mean the equivalent wattage and lumens which are almost always overstated. If makes me wonder if the actual wattage isn't understated as well since cynical old me can't help wondering why manufacturers should stop at 2 lies, especially as the 3rd is harder to detect. But all the interior LED lighting is working well and I have not had a single failure out of about 2 dozen light sources.
Now I come to the outside lighting where I have received the biggest (non electrical) shock. I installed some seriously weatherproof lighting along a verandah - made by the firm of Easy Connect. The lamp housing and cable connections are hermetically sealed against rain. I put up 10 of these with the original 35W halogen lamps in them. As soon as the first halogen lamp failed (2 weeks after installation) I ordered a dozen LEDs also supplied by Easy Connect through a mail order firm. At the end of the summer season 2013, 6 of the halogens have failed and 4 of the LEDs. This is so completely unacceptable that I can only point the blame at Easy Connect for selling lamps with virtually no quality control. I have 6 LED floods to illuminate trees and these are by a different manufacturer and not a single one has failed. The problem has to be with Easy Connect's quality control. Even more disappointing was the response of the vendors in France. I bought Easy Connect kit from a firm called Jardideco through Amazon France. There seems to be no sale of goods Act in France and mail order vendors can get away with anything. Even Amazon told me to get lost. Easy Connect and Jardideco referred me to the other. The floods that work were bought from a local electrical retailer. I have told every English friend I have in France about my experiences with LEDs and the vendors and my only grim satisfaction is that I have prevented sales of a few thousand â¬.
The biggest quality problem with all LEDs (including LED street lights) are not the diodes but the power source. Power source should provide also some protection for cases when sorounding environment is not the same as in the basic testing environment (heat, el. currents, ...). For details about street lights, please check http://www.luxtella.com.
I just installed 3 led bulbs into my bathroom light fixture. It is enclosed In glass, and the glass has turned a funny yellow brownish colour. Also the Celing paint looks warped by heat!! Maybe the bulbs are too strong for the fixture, or the glass is to enclosed, and that makes it too hot? I'm scared to open the glass can there be fumes that are toxic???? Please help!!!
My experience is that the least reliable part of any LED lamp is the voltage regulator. About half of them have failed in 6-12 months. As with CFLs, price and brand is no indicator of quality - the most reliable lamps so far were half the price of the least reliable ones.
That's unthinkable. LED lights are thought to be an advanced lighting equipment. http://www.ledlightshub.com/ LED lights from this site have a good reputation recently.
Life range can be measured by using higher voltage for burning and counting down estimated life range from this. Any one haven't time to wait for 25 years results :) I don't have experience for LED light tests but I as a consult I ordered tests for my customer cold cathode bulbs and got over 73000 hour result. They use military graded components and now they are making LED with similar quality component I let you know when get some results. I think by first impression that it will beat magical 50.000 hour limit easily. In these case could use electronic again, just change bulb on top. But safety issues and standards make it quite expensive. It has been thinking a lot since these bulbs start to have this long life range. And those problems can be solved, it just need again new standard on how to connect bulb and electronic parts together. In Europe, give estimated life range should base on test. Sadly, it seems not to work like that.
I had a play with several light fittings, It appears that the biggest problem for led bulbs (& cfl's too) is lack of ventilation - ie heat. Most enclosed fitting cause the lamp to quickly get far too hot to touch, no problem for an incandecent, but death for electronic components. Try putting your led bulb in the intended fitting, let it run for 15 minutes, then open it up and feel the lamp, if it's burning hot, it's no good! The best fittings are those that allow heaps of cool air to enter from below, and a big opening above, to let the hot air out. Sealed 'bunker' etc fitting are the worst. Again, if you carn't touch it, it's no good.
After a few short month my Sylvania LED light bulb which cost in the neighborhood of 30+ USD burnt out. LEDs look good on paper but I don't think they are worth the money yet, at least not Sylvania products.
I advocate energy savings to reduce the household bill anytime. I buy the odd LED floor lamp, the emergency LED flashlight, and an odd LED spotlight to test. Considering price over savings, I am more than willing to make the change for the longer term. However, equating price over quality does "irk" me a bit especially when LED bulbs "blow" out and yet have a lifesan of like forever. The other problem is LEDs lack the luminosity of an incandescent bulb. Unless the disadvantages are addressed and solved, its a while before I go all-out to change all the bulbs in my house.
LED standards are still being made. However, ALL standards reflect only the barest minimum, and do not include good design. If followed slavishly without imagination, there will only be minimum results. One of the reasons the late Steve Jobs was so great was because he included good design to make a fortune. Posted by lightvixen 0 seconds ago * Edit * Reply * Flag
LED standards are still being made. However, ALL standards reflect only the barest minimum, and do not include good design. If followed slavishly without imagination, there will only be minimum results. One of the reasons the late Steve Jobs was so great was because he included good design to make a fortune.
Waste. Of. Money. My Lemnis Pharox bulb started "strobing" within a few months of purchase. I have tried to contact them for replacement 3 times in the past 6 months, and they never respond. The warranty is supposed to cover failure. The $20 I wasted on this P.O.S. LED bulb would have paid for 2000 hours of electricity to power a brighter incandescent bulb.
Astronauts: http://oi54.tinypic.com/2qv6wsw.jpg Ocean: http://oi53.tinypic.com/35b9g08.jpg Thermometers: http://oi52.tinypic.com/2agnous.jpg Ice: http://oi52.tinypic.com/2upvlvm.jpg Earth: http://i49.tinypic.com/2mpg0tz.jpg Prophet: http://oi53.tinypic.com/b54in8.jpg Psychopaths: http://oi51.tinypic.com/2po8tas.jpg Thinker: http://www.youtube.com/watch?v=n92YenWfz0Y
I agree totally, as I've had the same idea for years. But I'm still waiting to see a standard 12-volt plug and socket combination, beside the car-lighter adapter that's impractical and way too big in houses (think extension cords and power strips for example). Actually this new plug would make sense in cars too, to get rid of all these bulky adapters filling all storage compartments. Then the same items could be used in houses and in cars.
Maybe it is time to rethink the wiring in our houses - a simple grid of 12 volt DC for lighting and electronics. One high quality transformer/rectifier power supply (with battery back-up) at the main panel. Just think of the simplification - no power supply in each computer, no wall warts for everything from cell phone chargers to e-book readers and portable phones. Wouldn't even need to buy a battery charger for the car battery! Just keep the 120/240V AC for the dryer, range, toaster, kettle, air conditioner etc.
I find it appauling that the (EC) is going to force consumers to put more money into the pockets of the giant businesses under the pretense of helping save the world. How about forcing these businesses to sell these products at a reasonable price first for a couple of years, then introduce a phase out of the incandescent bulb. But no.....lets make the people buy an expensive infearer bulb first then they will have to buy again and again while these companies try to get it right.
Works great, been there several years. Almost instantly full brightness during the summer. Takes about one minute during the winter, but it is still bright enough right off the bat. I don't see the problem.
The biggest problem I have with these "green" lighting choices is that they just aren't bright enough...When you put a 100 watt Incandescent bulb next to a "100" watt (actually only about 26 watts, but 100 watt light output equivalent) CFL and wait the 5 minutes needed for the CFL to warm up, it is clearly obvious that the CFL still just isn't as bright as the Incandescent...And try ti find a CFL that brighter than 100watts! I haven't! And what are we going to do about decorative light fixtures that use specific shaped bulbs? Like Marquis bulbs in the bathroom, or clear chandelier bulbs for that $10,000 light fixture...How are *THOSE* going to be lit? CFLs? Don't think so...LEDs? perhaps. but not today. What people are doing now in Europe is that they are stockpiling Incandescent bulbs...Once they become illegal for sale in Europe, people will still have 5-10 years of stockpiled bulbs to rely on...and the rest of the world will still be making them as well...so they aren't going to go away soon....but I can see black-market lightbulbs making a killing!
The world is a circle. Thomas Edison pushed the use of DC current. Photovoltaic generation is DC, most electronics are DC. LEDs are DC. Fuel cells generate dc. might as well start building new homes with all DC and get off the grid.
I installed an LED light in the fixture over my bathroom shower. It's been almost a year now and everything still works, the light does not seem to have reduced in brightness and it's in a really bad environment. Of course there's the issue of high moisture but even more importantly this light is wired in conjunction with the bathroom fan so there is all of the electrical "noise" associated with a cheaply made AC, shaded pole motor and the continuous switching spikes associated with regular short-term use. On another note, Lowes is presently offering LED light bulbs, on sale, for a little over $10.00 each. Not quite comparable to subsidized CFL bulbs but certainly a step in the right direction.
I've been using CFLs for several years now & never want to go back to incandescent bulbs. The combination of lower wattage for the same illumination & the longer life, even if they don't last as long as advertised, is a winner. An 80% reduction in electricity used (by an LED vs an incandescent bulb) is little more efficient than a CFL (23 watts for equivalent illumination to a 100 watt incandescent bulb)
LED longevity will always be constrained by the weakest link in the chain. All semiconductors such as microchips and LED's (electronic components) are part of a system chain that all individually require a well regulated low voltage power source which in turn is derived from the Global 100-240 AC power line in order for all the devices to operate within their specified design parameters. Electronic power sources contain many additional electronic components including but not limited to capacitors to filter out the AC line voltage ripple. When the specified lifetime of the existing electronic components used in low cost Asian made products such as CFL or LED lighting is only a few thousand hours at room temperature it is unrealistic to state or expect a 25 year LED system product life. LED lighting sources that are comparatively priced with CFL???s will not likely achieve a 25 year life expectancy in the foreseeable future without proper design of their power source and one that is protected from AC power line transients and has adequate thermal management all of which add cost. The question is will consumers pay the premium or will government subsidies last long enough to promote the right technology until economy of scale prevails.
Finally, the "experts" are realizing what consumers, like myself have been saying for a long time now. Do they really believe that consumers will shell out 40-100 x the cost of a regular incandescent bulb for a product that will not last the proposed lifetime of 25 years? The same canard was pulled on consumers with the CFL- huge cost savings, rapid return, saving energy and the environment were all of the mantras. The reality - the bulbs cost a lot of money, burned out rapidly (rapidly), produced poor quality light (in terms of luminosity/color), functioned poorly at lower temperatures and had prolonged warm-ups, attracted huge numbers of bugs (due to uv emission), were toxic disasters when they broke (due to the mercury), and created recyling nightmares, etc. While the LED itself may last a while, the cheaply made electronics will not. Sorry, but I'm not buying it.
I have used LED bulbs in various applications in and around my home for a few years (driveway lights, floods for backyard, accent lights) but, so far, I have yet to find any that are acceptable replacements for incandescent bulbs for general lighting. For that, I am testing halogen bulbs. So far, the results are fair. I refuse to use CFLs, besides the fact that they contain toxic materials, the light they put out gives me a serious headache.
Instead of screwing an LED "bulb" into a standard 110/220 light fixture, and having the bulb contain the electronics needed to step the voltage and current down, what's needed is either a) a small adapter that is separate from the bulb that houses the electronics that the bulb connects into or b) New light fixtures with the electronics built in, that standard LED bulbs could screw into. This would require coming up with a new standard for LED lighting so that they'd all be compatible with each other. This way you wouldn't be stuck with a fixture and no where to get a bulb for it in the future. But the standards committees usually love fighting over new standards so that would give them something new to do.
I attended an LED conference nearly 10 years ago. One of the topics was adapting LEDs to incandescent fixtures; the discussion did not provide any solutions. As the article pointed out, LEDs run on low voltage DC and the LED bulbs are used in standard AC fixtures. A better LED fixture system would convert AC to 12-15 volt regulated DC as a separate power system like that used for track lighting. A rough rule of thumb is that an LED drops about 2 volts and the current must be limited to less than 20-25 milliamps. The usual AC power fluctuates quite a lot and there are transient signals (noise) that can combine with the AC peak cycles to increase the actual voltage to be high enough to damage the LED; the same problem that can damage computer equipment. The life of LEDs is good but still prone to problems with decreased light output. CFL has similar issues and I have yet to get the full advertised life from a CFL. The LED industry is still developing and has made great strides in the past decade.
Overjoyed at the reduction in enegry consuption I would have for my annual display, I replaced all the incandescents. Definity different, colors, but I adapted. THEN, second year with "icicle" lights, I found the leads on the LEDs were steel, and rusted, often to the point of failure. Replacement made a serious dent in cost savings. The diode per se did not fail, but because of a poorly thought out design (minimal price being the driving gactor), the system failed.
If you could call it a standard, the standard plug for 12 volt in the US seems to be the old lighter adapter. That may be acceptable for now, but if 12 volt house grids become the norm, which I think is a great idea, then something a little more child safe might need to be designed.
Voltage determines how far you can reasonably transmit power without too many losses. That's why all electric power transmission lines use high voltage. It's basic Ohm's law. By the same token a 12V system in the house won't work - AC or DC. The losses get to be unacceptable after about 30 feet or so. The halogen low voltage lighting systems commonly installed in houses today run into this issue. The low voltage power supply can't be located too far away from the lighting.
Your thought is good but................... a TV for instance needs more voltage than a radio or a table lamp , a basic smaller screen computer needs less voltage than one that is loaded with a bigger screen. A small portable table top fan would require a lot less voltage than a larger floor standing fan. So as 12 volt for basic lighting thoughout the house might have some merit, a standard 12 volt plug-in for everyday appliances does-not.
I agree that consumers should not be forced to buy these bulbs. It is not about forcing consumers to put money into the pockets of businesses, though. Seriously, I do not know why so many people are anti-business. Big businesses advancing this technology is pretty much the only chance it has. Why would anyone be against big business when that is exactly what our economy needs right now? We need jobs. Where do you think those come from? Forcing a business to sell them cheaper is as bad as forcing consumers to buy them. I find it appalling when a government forces businesses to put more money into the pockets of consumers under the pretense of helping to save the world. infearer? really? inferior...
In my opinion, modern homes are overlit. We've had 10W CFLs here for years, and slowly replacing them all with 5W LEDs. The trick is to lower the light fitting on a cord, and direct the light right where you actually want it instead of overlighting the entire room so you can read in its dimmest corner...
Edison was a great inventor, to be sure, but in his own mind, he was an ultra-fantastic inventor and always right ! He bitterly opposed Tesla and Westinghouse who were pushing AC over Edison's favored DC. However, DC just doesn't transmit well over 20 miles or so without drastic losses, a problem Edison couldn't solve. There are things AC will do that DC can't, and vice versa!
The lifetime of an LED chip depends on temperature and therefore drive current. Many LED designs have made the mistake of trying to achieve maximum brightness by pushing the chip to it's limits. Some designs suffer from spikes in the mains supply getting through to the chip and taking them out as you say. The lifetime of CFLs and for that matter incandescent bulbs in my house has been very short for presumably similar reasons - transients. All of this is quite avoidable, and an issue of good desing and of cost tradeoff. LED lighting works quite well in the well designed devices, and badly in others. I have had mixed results with LED lighting but it is clearly the right answer out of what is available now. It's not like LEDs are new - they have been around for a long, long time. It is only the high output and the white LEDs that are new. I have 1 lamp that works fine. I have LED strip lightin in the kitchen, cost $20 per 3 strip. I set works perfectly, the other has a problem in the switch on the low voltage side and sometimes only half the LEDs illuminate, which I can obviously fix quickly by taking out the switch or I could have returned them and got a new pack. I have one porch light at the front door which was good until it developed a fault that results in the light flashing. It ends up looking like a strobe for an alarm. I must sort this as it was a great light before that. So yes I acknowledge there are issues to sort, but LEDs are not inherently short life. In reality we all have LED lighting that mostly has functioned for decades with never a thought about it failing. LED indicators have been a standard feature on consumer electronics for several decades and the failure rate is low. It is purely pushing their use at low cost with a disposable power supply included and at the highest possible light output that is resulting in poor design & cost cutting. What is obviously needed is to stup trying to put 3v bulbs into 120v/240v outlets and move the design of fittings towards a sensible replaceable LED system. I suspect nobody is prepared to set the standard yet though due to the rate of change.
Yes I get headaches from flourescent tubes. The newer CFLs are fine for me. It is the flicker mainly that is the issue, although the average FL tube had very bad colour temperature, as did the early CFLs. Since consumers drive the CFL market they have moved to what those experiencing the light will buy. The FL tube market is largely driven by offices where the decision is made on cost by those that don't have to live with the consequences.
Your problem with the compact fluorescent bulbs is 'flicker'. Every AC light bulb flickers. That means that the bulb brightens and dims with the variance of the current. There are high speed videos that can show this happening with standard incandescent bulbs. Fluorescent bulbs have a much greater light output change between the parts of the cycle. The human eye is commonly sensitive to flicker at between 20 to 30 hertz. That's at a conscious level. at a sub conscious level, it can be a problem at higher frequencies. The constant strobe light effect does cause strain, and can in some people induce seizures. Fluorescent desk lights have been known to do this for decades, for some people. Also, cold ambient conditions magnify the effect in the bulbs. The effect can be fought by either increasing the frequency, or the power level in the ballast. Both of these are done in commercial 48" fluorescent fixtures. Neither is done in inexpensive CFL lamps. Most LED's use frequency multipliers, so they 'should' not have this problem. I hope that helps you.
120 V AC is a curve, part of which is pure low-voltage DC, just what LED's require. If the electronics switched on for that low-voltage, properly-polarized portion of the power curve, every sixtieth of a second -- and OFF before the voltage rose in the curve -- then the LEDs could get what they need (using a simple resistance-capacitance circuit to store and smooth the pulse) without hardly touching the main power curve, much less "controlling" it down to the level they need it at. This could also make LEDs much more practically efficient than they are now, as they wouldn't have to waste so much heat. (still no solution for the life-dimming problem, though) Isn't it amazing, when one mind can solve a "problem" that's been plaguing a whole industry for years? Go ahead, take it to an electrical engineer -- only way to prove me wrong...
Have a look at the packet for your lights, they tend to have a 1 year warranty, It makes them sound good, until you realise that by the time you get them out for the next festive season, the warranty is up! ie, in reality, for outdoor use, they will die in 1 month, so much for 25 years of life.
I did spell that wrong didnt I (Brain Toot) oh well life goes on Anyway I cant believe you think its wrong for the Gov to force a business to sell a product that does what it says it does at the high prices they are charging for it and these new LED bulbs DO NOT. You can't stimulate the economy by screwing the public. I bet you buy alot of products from China and think there great ..Don't Ya
With modern technology, DC actually transmits over distances better than AC. I agree with NoSacredCow that we should move to an all DC world.
I know you think it sounds like a good idea,but it isn't and would have serious side effects. What happens when hundreds/thousands/millions of these lights all draw current for a millisecond once every 1/60 of a second... and remember, all at the same time? You get a serious current/load spike on the electrical grid, distorted voltage waveforms and radiated noise. consider how much current you need to draw for one LED, 20ma needed continuous, but for the 1ms (out of 17ms available between pulses) means you need to draw 340ma (~1/3 of an amp) for that 1ms to "smooth it out" and provide 20ms for a full cycle. start doing the math....
Congratulations, you've just 'invented' the regulated power supply. Every single LED light bulb for use in an AC fixture already has one of those in the base. SCR and capacitor provide relatively even DC output for a variable AC input. The problem comes when the input exceeds the design limits of the power supply. it is common for an AC system to drop for a fraction of a second to around 50% of standard rated voltage, or to rise to twice or more of the rated voltage for a small fraction of a cycle. Something like this happens every time your Air Conditioner turns on. Surges happen. Every time they do, the components degrade a little bit. eventually, they degrade enough to break down. Sorry, it's just physics.
Usually specifies no more than 8 hours continuous use, and 'seasonal' use. I've had strands last up to 18 months continuous inside, somewhat less outside. Newer and pricier strands have replacable LED's, but there always seems to be a percentage of failing diodes in any multi-diode device. I just want the manufacturers of all lights to give me lumens/watt/hr data. You also save nothing with any new lighting if it is in a place where the luminaires are readily broken....
The problem with LED lights right now is one of scale. The production runs are much lower than those of CFL or incandescent bulbs. As the production runs ramp up, the price should come down. It has already come down from around $50 per lamp to around $20 per lamp. Cost of materials should lower it to around $10 per lamp over the next few years. Quality issues will be resolved using automation. The higher prices are because of hand assembly. The push for LED lighting comes from the 'green' movement, not from any desire to stimulate the economy. 'Green politics is frequently more about the emotional high from thinking you are doing something than about real measurable improvements. Yes, the lumen values used for comparisons are skewed to favor the new entrants. A realistic comparison is that a '100 Watt equivalent' bulb is really a 60 W equivalent. All lighting professionals know this.
sorry but. the reason we use HVDC for "inter-connect" is mainly to isolate the two power grids from having to maintain the same phase and thus affect each others stability. HVDC can run at a lower voltage level than HVAC for the same power transfer, making for less expensive insulation costs... or, at the same voltage, transfer more power at the same current (though conductor size would be increased). The comment on DC being more dangerous is backwards... AC is conducted by the human body easier than DC (in fact, the human body has it's least resistance at ~50Hz... we picked a bad choice for power line frequencies if we wanted safely).
...There is a marked safety issue as well, here. AC shocks can most often be weathered without physical damage, where the same amount of power in the form of a DC shock can cause significant damage to a person; most often in the form of deep-running electrical burns. With AC, the real power points on the AC curve only take up about half of the waveform, while the AC "vibration" you feel warns you of the shock current. Whereas with DC, the power is immediately ON, and does not go OFF until the contact is ended. Also, there is no "vibration" at all, meaning that the fact you are hooked up to power is not so obvious. DC CAN be useful at low voltages, as the discussion on LED's makes plain, but at higher voltages, the death-dealing-shock danger goes up precipitately.
What can be done commercially with high-voltage DC electricity transmission cannot be used in the home. DC is notoriously difficult (=expensive) to change the voltage, so is not well suited for high demand home applications such as air conditioning or cooking. This is why most power transmitted over HVDC transmission systems are converted from DC to AC for the end user.
There is an AC power line a few miles from my house that connects to Page Arizona (400 miles away) which also connects to Los Angeles California (a little over 500 miles away). This would seem to show that AC power can and does transmit well. the big advantage of AC over DC is two fold. First, AC power only needs a coil of wire (Transformer, but, a piece of iron makes it more efficient) to change voltages. Power losses in both AC and DC systems are a function of the current. AC systems take advantage of the transformer to raise the voltage while lowering the current (constant power). This means that it is simple to raise the voltage to very high levels and transit large amounts of power over long distances. That's why a single power line can carry all of the output of most generating plants. Nicoli Tesla worked all this out over 100 years ago. Edison just didn't understand the math. High voltage DC systems are possible, but are quite complicated in practice. That's why AC wins out over DC systems in anything over a mile, and under a million volts. It's simply cheaper to run AC and convert to DC when you need it.
This is called power factor. The energy needed to be supplied is near enough to cover the same load for the whole cycle - so in effect you would multiply the demand requirement enourmously. In Australia for instance the large users are billed in such a way that this would affect their billing and so they would have to install power factor correction units to even out the load. These are large devices and very heavy and expensive. Domestic electricity metering doesn't take this into account and so the efffect is there to the grid but the consumer doesn't pay for it. There are shonky devices on the market aimed at consumers that offer to reduce electricity bulls by correcting the power factor. What many devices do to put low voltage LEDs in mains fittings is to put the LEDs in series. This is what christmas lights do, this is why a small low voltage light works on 110/240v and why you need every globe to be working for any to work.