Making Strides Toward Low-Cost LED Lighting

Roland Piquepaille writes "You all know that incandescent bulbs are pretty inefficient, converting only 10% of electricity into light — and 90% into heat. Light-emitting diodes, or LEDs, could soon replace incandescent and compact fluorescent bulbs in our homes. They are more efficient and environmentally friendly. But LED lights are currently too expensive because they are using a sapphire-based technology. Now, Purdue University researchers have found a way to build low-cost and bright LEDs for home lighting. According to the researchers, the LED lights now on the market cost about $100 while LED lights based on their new technology could be commercially available within a couple of years for a cost of about $5. It would also help to cut our electricity bill by about 10%."

LED = Luxury Goods

Take a hint from the car manufacturers. Today, high-end cars are using LED tail lights. They are also used on trucks. The main advantage is they do not burn out.

However, for most people in the world a burned-out tail light bulb is a minor safety issue and a minor expense. Replacing the bulb takes 10 minutes and maybe the owner's manual if you are truely clueless about how to do it. Also, many people own a car for 5+ years without ever having to replace a single bulb.

Compare this to the cost of a minor traffic accident where a tail light is cracked. No, you cannot replace the lens or any individual part, just the whole assembly. Instead of $100-$200 for an incandescent bulb assembly expect to pay $1500-$2000 for the LED tail light.

Sure, over the life of many vehicles it is a minor issue that bulbs will never burn out. But over the same number of vehicles it is far, far more likely that a lamp assembly will have to be replaced. The result is a far more expensive part to replace.

With trucks there is a certain amount of sense to be made with claiming that the bulbs do not have to be replaced. Replacing a bulb on a truck or semi-trailer can be a real hassle requiring a ladder and tools. However, again the likelyhood the bulb would ever need to be replaced vs. the lens being damaged is about the same as for cars. Basically, it is a complete rip-off.

Expect to see wired-in LED systems in household lamps where the fixture must be replaced because the bulbs cannot be. Expect to see the fixtures sold to builders with non-replacable bulbs will cost the builder only slightly more when bought in huge quantities but the homeowner will be faced with $1000 lamp fixtures should they ever need or desire to replace them.

Re:LED = Luxury Goods

Trucks use LED taillights because they are more visible in the daytime. It never ceases to amaze me how often a 4-wheeler (car driver) will rear-end a truck that is braking for a stoplight or turn, then claim that they didn't see the truck's brake lights.

The LED taillights you see on a lot of semi-trailers are held in place by metal bezels that are riveted in place by the manufacturer. To replace one, you have to drill out the rivets. Then of course you can simply use self-tapping screws to put the bezel back on once you have replaced the light. Incandescents tend to be held in place by a rubber cup-like thing that I don't know the name for, and can be removed by prying on the light with a flathead screwdriver, much like dismounting a tubeless tire from a wheel.

The reason for riveting the things in place is to deter theft. Incandescent lights don't get stolen nearly as often as LED's for some reason.

Re:LED = Luxury Goods

They are. I've seen some in nightclubs and at concerts, the brightness and the instant on/off effect is fantastic.

It's probably even better with ecstasy.

Don't market these in Boston

They really have a phobia about LEDs there- especially if there are wires attached like an AC cord.

Electricity savings ?

I realise it's customary not to RTFA, but I would think that the submitters would at least read what they submit. Roland wrote:

It would also help to cut our electricity bill by about 10%

The article says:

a technology that could cut electricity consumption by 10 percent if widely adopted

Far from the same thing. But I suppose that's another reason people don't like Roland.

Do LEDs blink ?

Today for the first time I noticed a car with blinking tail lamps. When I say blinking, I mean it was blinking as fast as a CRT monitor, but the problem is that I can see it. I'm one of those people who has never been able to stand CRT monitors at less than 100 or 120Hz. I also have a hard time with some fluorescent lighting. I suspect what I saw was the lousy application of LEDs on the backside of a car.

So, suck it up, I hear you say. Right, except that each blink leaves an annoying remanent patch on my retina that lasts for a few seconds. Imagine driving at night in a city, 10 cars in your field of vision, look left, right and suddenly you have 200 spots in your field of vision. Awesome to know what's going on, right ?

I loathed the xenon high beams when they first came out a few years ago. You know, those tiny very concentrated blue lights ? Leaves a retina trail that lasts for 20 seconds. I'm so glad that they are gone now. I've never heard if they were made illegal or if they just went out of fashion, but I hope LEDs (which are a good technology) are applied in a good way...

Re:Do LEDs blink ?

I loathed the xenon high beams when they first came out a few years ago. You know, those tiny very concentrated blue lights ? Leaves a retina trail that lasts for 20 seconds. I'm so glad that they are gone now. I've never heard if they were made illegal or if they just went out of fashion [snip]

Xenon HID headlights never went away. They're still standard equipment on higher end Japanese and some German luxury cars and optional on many others. If anything, their use by car manufacturers are expanding, not contracting.

What YOU'RE complaining about, and thankfully seem to have gone away, are those high intensity blue color lights that dropped into a standard headlight assembly. Like you mention, I don't know if they were made illegal or became "uncool" but I hated them as well. True Xenon HIDs have a completely different reflector assembly than standard halogen headlights and spread the light far more evenly and are actually less annoying that a slightly misaimed halogen headlight, and you probably see them all the time and don't even realize it. They look "blue" only compared to what turns out to be the yellow tinge of a regular headlamp, but at a glance just appear very white.

Re:Do LEDs blink ?

What you are seeing is the pulse-width-modulation dimming of the taillights applied with insufficiently high frequency. Cheap chinese flashlights like the Jetbeam C-LE (which has gone through three revisions prior to current - and is an absolutely excellent little LED torch) have been using increasingly high PWM frequencies to get around that; more expensive ones use current regulation (which averages the current of the PWM circuit over a few tenths of a second to produce a flat current (and therefore brightness) curve when viewed on an oscilloscope. The advantage of lower PWM frequencies is that the eye hands them off to the brain via a high-priority nerve link that results in people noticing them significantly (tenths of a second or so, IIRC) faster, theoretically reducing both the number and severity of accidents. The fact that many of them are bright enough to impair normal night vision seems to be lost on auto designers.

HID headlights have not gone away, but their implementations have been getting better - projecting beams on a down-angle so they don't nail people in the eyes, lowering the operating temperature of the bulb, making them less blue and more yellow-white without making them dimmer (actually, lower-temperature HID bulbs are more efficient than the blue-tinted ones). HIDs are popular for bulb life being insane, since headlight replacement was getting to be a significant drain in carmaker's warranty claims, and being brighter and having a longer effective range, which is good when there's no streetlights.

Entirely different is the blue-tinted halogen bulbs that are simply normal bulbs with a light blue paint applied - these are the ghetto-fabulous attempt to make it look like you've got an expensive HID conversion for an older car, and are about 30% dimmer than normal halogen headlights despite being harder on other drivers' eyes. I have no forgiveness for people who use these because they think it looks good.

LED already cost-effective in some situations

LED lighting is already cost effective in certain situations. I priced a cable-hung low-voltage lighting system using LED-based MR-16 socket bulbs vs. 12 volt halogen incandescent and the system pays back in less than a year in electricity savings. That doesn't even count the significantly smaller number of bulb changes that are required.

If you have a large number of low wattage/low voltage light sources, CFL is not viable, but LED is. The power requirements are so much lower that smaller transformers can be spec'd, you can string piles more of them on a circuit, saving even more money.

There are some neat bulbs available at http://www.theledlight.com [theledlight.com].

Re:Yea,

They will be way more environmentally friendly. No mercury involved.

Re:Yea,

No mercury = huge improvement

Re:Yea,

But how much of an improvement will they be over fluorescent lights, which we already have at an affordable price?

Well, they won't flicker, they won't contain mercury, and they won't be too big to fit in many light fixtures.

Even if LEDs aren't any more efficient than current CFLs, they'll be a lot more attractive to people who don't like or can't use fluorescent lights.

Re:Yea,

Also, TFA states that LEDs have the potential to well surpass fluorescent bulbs in terms of energy efficiency.

Another article http://pubs.acs.org/isubscribe/journals/cen/86/i28/html/8628cover4.html [acs.org] provides some interesting information on organic LEDs - OLEDs have interesting design applications since you can make them in flat sheets

(I think an illuminating wall would be way cool, but maybe thats just me :-))

Right now efficiencies are similar to the inorganic LEDs and fluorescent bulbs.

Re:Yea,

not just an illuminating wall. Imagine the entire ceiling covered in an OLED sheet and have lighting do cool stuff like follow you around or whatever. Rooms with people get lit while others don't. Crazy flashy lights for parties. the possibilities are limitless!

Re:Yea,

Well, they won't flicker, they won't contain mercury, and they won't be too big to fit in many light fixtures.

2003 called, it wants it's CFL stereotypes back.

CFLs don't flicker like old ballast-type fluorescent tubes of decades ago. And the newer ultra-compact ones are actually smaller than the incandescent bulbs they replace. I have one in the swing-arm desk lamp in front of me right now, and the tip of the bulb no longer protrudes past the end of the shade like the old bulbs I used in it long ago. In my bathroom I have CFL bulbs made to look identical to G25 globe lights, in the same fixture with the actual incandescent bulb I am slowly replacing. They appear the same except the CFLs are brighter and their light isn't as yellow.

I will give you the mercury, though.

Re:Yea,

The mercury depends on efficiency aswell. Modern CFLs have <=2mg mercury content, (at least the CFLs I own). Over a 5 year period, the electricity needed for CFLs, generated by coal based power plants in some portion, releases 2.4mg of mercury into the air. For incandescents the number is 10mg over a 5 year period. LED lighting is currently less efficient than CFL, so more mercury gets into the air.

The question is really, whether you prefer 2.4mg of mercury in air plus 2mg in the landfills, or more than 2.4mg of mercury in the air. Until LEDs become more efficient than CFLs, I'll opt for CFLs.

Note, there is a confusion over LED vs CFL efficiency. LEDs generate light more efficiently than CFLs, but they do so in a narrow arc. To make it useful for everday applications conversion to a wider arc takes place and that causes efficiency loss.

CFL Color

you need to look at the Color Temperature when you buy CFL bulbs. A CFL rated at 2700 degrees Color Temperature will look almost exactly like an incandescent light. A CT of 3000 degrees is called a warm white and is very pleasing. A CT of 4000 is called a cool white and looks a little bit blue. And a CT of 5000 degrees or more is about the same color as Sunlight and appears to be very blue indoors.

I really like the color you get when a 2700 & 5000 degree light are in the same fixture, everything looks bright and colorful.

Re:CFL Color

Not perceptions... Quanta [wikipedia.org]

Look at the sun and at a CFL though a spectroscope. With the sun, you'll see even intensity across the spectrum. When you look at the CFL, you'll see several distinct bars of light at specific wavelengths. While both average out to about the same color temperature, the sun will have a black-body spectrum, evenly illuminating the pigments in the items in your room, while the CFL will make certain colors in the room jump out more than others.

Re:CFL Color

Here's some links:

A white LED's spectrum [sci-toys.com]

A CFL's spectrum [sci-toys.com]

Re:Yea,

Well, they won't flicker, they won't contain mercury, and they won't be too big to fit in many light fixtures.

Even if LEDs aren't any more efficient than current CFLs, they'll be a lot more attractive to people who don't like or can't use fluorescent lights.

Have you actually looked at high-quality CFL bulbs? A good daylight bulb is a thing of beauty. No flicker (and, you know, CFL bulbs have never had flicker because they are run at much, much higher frequencies than you visual sytem can see), proper color balance, small, reliable, quiet.

Note that I'm not talking about the two or four foot long fluorescent bulbs that you might have in your office. Those are probably not daylight balanced and probably flicker at 120 Hz (yes, 120 Hz, not 60 Hz, because both half cycles push current; unless you're in part of the world which runs on 50 Hz mains, in which case they flicker at 100 Hz). Their ballasts also have a tendency to buzz.

Good CFLs are wonderful.

Note, also, that many LED bulbs you can get these days are simply awful because they flicker at 60 Hz (yes, 60 Hz, because they're arranged in cascading diode fashion and only conduct on every other half cycle) and the phosphors are terrible. They also lose brightness at an astonishing rate and are horribly temperature sensitive (hotter chip, lower light output). The 60 Hz issue can certainly be fixed with better circuitry (ie, bridge rectifiers and some low-pass filtering) and one hopes that the phosphors and lifetime improve.

Wait, phosphors in an LED? What am I smoking? Yes, it's true, most white LED bulbs for sale are actually UV emitters that excite phosphors. And just like fluorescents, the better the phosphors, the better the output spectrum. While it is possible to generate white-ish light from a combination of red, blue, and green LEDs, because the aging curves are different for the three classes of emitters, the color balance is dynamic over the bulb lifetime. And, also, the spectrum is terrible -- even the spectrum from fluorescents is better -- because it's essentially three isolated wavelengths instead of a continuous spectrum.

LEDs have a long, long way to go before they can be used in living or working spaces.

Re:Yea,

In addition the no mercuary as already noted, they will have a longer life, be less fragile, and be smaller.

Re:carbon-free daytime lighting

With the cost of solar cells and LEDs plummeting, a solar cell roof installation with closed-circuit LEDs might soon become cheaper than a ceiling window.

What do you know! Soon enough it'll all get so efficient that with closed-circuit LEDs shining on solar cells you'll be able to make your own infinite source of energy!!

Oh shit that's a hell of good idea! The first one to the patent office wins!!

Re:Is it white, though?

Many of these white LEDs are blue or UV LEDs that stimulate a phosphor coating to produce white light.

Having three Red Green Blue LEDs to create white light might produce a light that appears white to the eye, but might not have the same effect when reflected off material.

The white from the phosphor would generate more of a broad spectrum white, whereas the Red, Green and Blue LEDs would probably create spikes in the Red, Green and Blue spectrum.

So you might have a green material that appears black when you use the "RGB white" LED - just because it does not reflect the Green LED's narrow green, whereas it will appear green in the white from the phosphor white LED.

The phosphor means one more step in light conversion, and that probably means less efficiency.

Re:Is it white, though?

As far as I know, the most used variant is the blue LED + yellow phosphor one. In this case, the blue light, emitted by the LED, is cast directly, besides the yellow light coming from the phosphor. The mix of blue and yellow produces white light.

Unfortunately, these LEDs don't produce a very broad spectrum of light either. The spectrum has a sharp peak in the blue range, and a bit broader yellow range, as can be seen on this graph on the Wikipedia page [wikipedia.org].

Re:It's Roland the Plogger, wrong as usual

Uh...the linked article is on a purdue.edu page and has zero adds. Am I missing something?