If you'll scroll down in this thread to a post called "Ralleia!" you'l find some opinions, offered by a lighting engineering student, on the topic. The general gist of it seems to be that LEDs for use in general illumination are rapidly improving and show a lot of promise, but aren't ready for prime time. Fluorescents are still a far better choice, when you factor in the cost of fixtures, and most people find the light quality rather poor.

LEDs show great promise for the future, but they won't save you a ton on electricity just yet.

I just went through a three-day exercise to see if I should use LEDs for plant grow lights, and here's what I found about their electrical efficacy:

Red LEDs were best at 55 lumens per watt (lpw)
White LEDs were 25-29 lpw
Blue was weakest at 10 lpw.

They were also way too pricey. From my calculations, a single 40W fluorescent tube produces about 3200 lumens, last about 3.5 years and cost about $2. In order to generate the same amount of lumens of red light, it would cost me over $600 initially, burn more electricity, though it would last 13.5 years. For white light, the cost would be about double the red light for the same number of lumens.

For reference, lumen efficacy of other common lamp types are:

standard incandescents : 5 - 18 lpw
tungsten halogen: 15 - 25 lpw
low-wattage compact fluorescent : 20 - 55 lpw
high-wattage compact fluorescent : 50 - 80 lpw
linear fluorescent : 65 - 95 lpw

There are a couple other types of high lumen output standard lamps (sodium, metal halide, and mercury vapor), but their lengthy on-cycle time makes them unsuitable for interior household lighting (meaning it can take 2 - 20 minutes for them to come up to brightness). They also aren't very good at producing "white" light.

All that being said, LEDs have been doubling in lumen efficacy every 18-24 months, while the price has been decreasing by 20% per year. By about 2010 white LEDs should bust the 200 lpw mark, while the price will have dropped exponentially as well. At that point, many people (including me!) will find LEDs irresistably attractive.

"Fluorescents are still a far better choice, when you factor in the cost of fixtures, and most people find the light quality rather poor."

The newer, better flourescents seem to me to produce a very good quality light. We use them in a lot of places and plan to use them in our remodeled kitchen -- assuming we get it done before the LEDs are ready for prime time. ;-)

Sorry, I wrote unclearly. I meant that LEDs' light quality tended to be rather poor. I agree that fluorescents have come a long way.

LED's are great for battery lights because they produce a fair amount of light with the reduced voltage when a battery is half discharged. An incandesant bulb would barely glow and a flouresant wouldn't light at all under the same conditions.
This gives the impression to most people that LEDs are super efficient. That is not true. and may never be true. Every technology has a limit. Although they will certainly be improved over what's available today.

for house lighting with a constant voltage supply, fluoresants are still much more efficient.

There are efficient lighting products on the market already and they are not viewed as upscale. Recessed incadescent cans, halogens, track... make more efficient space heaters than lamps but people like them better. So they may be getting better, whiter and cheaper but the big question I would have is will they be used in as many applications as even compact florescents and I don't think so.

How do people like the Christmas LED lights? They are flying off the shelves in my city and the electric utility has provided incentives for "trading in" your traditional lights. I hope the energy savings are real, because I find the quality of light rather cold and strange, just not Christmasy enough. The red and yellow ones are OK but the blue and white ones hurt my eyes. JMHO.

LED christmas lights may be a great application for led's. Not so much because of the energy savings, but because of the life of the bulbs. Every year i spend hours swapping bulbs trying to get last years lights to work. I'm too cheap to buy new bulbs until I'm absolutely certain last years lights don't work and by that time the stores are closed and I have to make the old ones work!

I get a lot of comments about the LED christmas strings we use outdoors. They're actually fairly inexpensive Chinese-made lights (are any of them made anywhere BUT China???), and the faceted plastic "raspberry" covers over the too-directional LEDs don't provide very good light diffusion. Thus a few of the individual lights - the ones aimed just right - jump out at the viewer, while others are of rather mediocre brightness. Against a dark house on our dimly-lit road, they're still plenty bright.

What usually catches the eye is the intense, highly saturated "blueness" of the blue LEDs. It is a thing to behold. The reds are also good. The yellows and greens are a bit wussy.

We have no white LEDs. It seems to me that the light from them is so cold that it would make convincing stars - and that's about all they'd be good for.

Ours also have a pronounced 60 Hz flicker. LEDs are a DC device. These simple light strings appear to be nothing more than 70 series-connected LEDs. I don't think they even have a blocking diode, unless one is hidden in the plug, which suggests the LEDs themselves may be a bit out of the ordinary (I've read that most LEDs don't do well when reverse-biased). A full-wave rectifier on the input might improve the appearance, but I haven't tried that yet. (It might also overheat them by exceeding their duty cycle.)

The good news is that their energy usage is trivial. I'm very happy about that and will continue to use them.

I'm having some pretty great results with LED lighting. Much, much better than T-5 fluorescent. See my web page at http://www.greenpinelane.com for pictures of my aeroponics with LED lighting. I'm using 630 NM for Red and 470 NM for Blue. I never got great tomatoes using fluorescent and the LEDs are comfortable on the eyes and electric bill. Each red light is 15 Watts and blue is 3 watts usage.

I am a lighting Designer for the entertainment industry and have a fair amount of LED lighting in my home and garden. One of the issues that most aren't aware of is that LED in it's nature is very color specific. I have produced a seminar using a childs rubber ducky, I will hold it up in front of a traditional source amber light and it will appear as you would expect. I will then use a color mixing (RGB) LED fixture to make the same Amber color. When I hold the duck up in front of the LED it becomes quite red, the name of the seminar is Evil Duck ;). The reason it goes red is because the LED's are mixing Red and Green to make the perceived Amber, problem is that no Amber light source is actually involved so there is no Amber for the duck's pigment to reflect. It uses the Red to reflect the Red in its pigment. Unlike most other common sources of light, LED is a single frequency source of light to begin with and many clients are surprised how things "appear" under LED lighting. Just a cautionary note for some. Peace, Tony

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Found an interesting site talking about LED lighting. Some interesting numbers.

Fluorescents do about 80 ~ 100 lumens / watt. Incandescents do about ~17 lumens per watt. Some "hot" LED's on Ebay are doing ~ 60 lumens per watt.

One caveat of LED's and their "intensity" => usually measured in Candelas => that is; over a specified beam angle; essentially they are "directional". An LED advertised at 130 candelas sounds great . . . but it's over ~ 12 degree beam width ( narrow ) => light output is ~ 4.5 lumens ( lumens is "overall light" . . like radiating over 360 degrees ). It's just concentrated in a pretty narrow beam but will not "area" light much.

Also states that LED's are presently about 100 times the cost per lumen; of a decent fluorescent light.

We're not there yet . . but with prices dropping ~ 20% / year; it's coming sometime.

Right now; they are good candidates where only a relatively small area needs illumination; and that lifetime is a concern => they will typically do 100,000 hours ( 10 YEARS ) if you treat them reasonably.

Decent web site with links to all kinds of stuff including mfr's websites and show and tell stuff for what's coming up . . . .

Bob

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i think Led lights is a great replacement of Incandescent,it is more evironmentally friendly and can save more energy, it is best choice for many uses

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LED's (Light Emitting Diodes) have revolutionised energy-efficient lighting using on average 20% (or less!) of the energy required to power a traditional filament or energy saving lamp but offering a comparable or better light output.

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