LED lighting, effectiveness and efficiency

2009-10-23

in Economics, Geek stuff, Science, The environment

Perhaps the only thing that will ever silence the various overblown objections to compact fluorescent lights is when they are replaced by solid state lighting systems, based on light emitting diodes (LEDs).

Unfortunately, as a post on BoingBoing points out, there is still a way to go before such lighting systems will be viable options for most people. For one thing, they are still expensive. For another, the light they produce may start out not being white, or drift away from being white over time. Worse, it is very difficult for people to distinguish between high and low quality products currently on offer.

Another problem is that LEDs aren’t unambiguously more efficient than fluorescent lighting systems: “The more lumens per watt, the better the energy efficiency. The kind of fluorescent lamps used in offices–the long, narrow ones that are called T-5 or T-8s in Technicalland–regularly get more than 100 lumens per watt. An LED T-8 lamp tested by CALiPER last year got 42.” It seems those of us pushing for more energy efficient lighting may have to continue rebutting claims about mercury and flickering for some time yet.

Report a typo or inaccuracy

{ 54 comments… read them below or add one }

Anon October 23, 2009 at 8:13 pm

How do halogen lights measure up?

. October 23, 2009 at 8:48 pm

Disadvantages

* High initial price
* Temperature dependence
* Voltage sensitivity
* Light quality
* Area light source
* Blue Hazard
* Blue pollution

Matt October 25, 2009 at 6:10 pm

The ~400Hz at which compact fluorescent operate is, in my view, imperceptible in terms of flicker. I’ve replaced nearly all the bulbs where I live with CFLs, at a fairly high initial cost. So far I like them, although some of them (the ones encased in a ‘light bulb’ shaped exterior) take a minute to give off a normal level of light. Also, one outdoor one has failed after only a year.

In my final year of university, one of my friends did their final project building a prototype drop-in replacement LED tube, meant to replace fluorescent tubes. She found that the replacement was indeed worse than the original for efficiency. As well the highly directional nature of the LED gave off weird light.

I think that while CFLs have critics, they have also gained a lot of acceptance. I see them frequently, and I think more people will buy them. Many places have building codes that require their use in new builds.

As for halogens, they need to be hot to work right (hotter than a regular incandescent bulb). While they are more efficient than a regular bulb, and have longer life spans, most of the energy goes into generating heat, not light.

Milan October 25, 2009 at 6:12 pm

Thanks for the information.

Milan October 25, 2009 at 6:16 pm

I have replaced all my incandescent lights with CFLs, except the small ones in the chandelier in my dining room. It takes unusually sized European bulbs, which are hard to find even as standard incandescents.

Tristan October 25, 2009 at 11:19 pm

“While they are more efficient than a regular bulb, and have longer life spans, most of the energy goes into generating heat, not light.”

All light is heat. Electromagnetic waves both inside and outside the visible range are all “radiant heat”. What you mean is that most of the energy goes into generating heat that is not light. From an efficiency standpoint, it is meaningless that “most” of the energy is generating non-light heat. It is only meaningful that less of the energy is coming out as light compared to an alternative.

Matt October 26, 2009 at 1:29 am

I think it’s apparent, in a practical sense, then difference between “heat” and “light” the way I was using them. That is, a light bulb is a device used to produce visible light. An undesirable trait is that the bulb gets hot. In an incandescent bulb, the fact the filament is hot is what makes it produce light. More efficient lighting doesn’t require this heat to produce light, because it works on different principles.

I think it is disingenuous to say that “all light is heat”; it is not. Light is electromagnetic radiation, as are radio waves, x-rays, etc… Heat can be transferred by electromagnetic radiation, but electromagnetic radiation is not heat. Heat is rather a form of kinetic energy in which individual atoms (that is, matter) vibrate and move in other ways. Absolute zero is the temperature at which this motion would cease.

In addition to heat transfer by radiation, there is heat transfer by convection (heated matter physically moving from one place to another), and conduction (something hot touches something less hot, and transfers some of its heat). Just as it would be inaccurate to call a warm breeze ‘heat,’ it is inaccurate to call light ‘heat.’

Milan October 26, 2009 at 8:39 am

An experiment to illustrate that light is not heat:

1) Take a cast iron skillet and put it in the over at 450˚

2) Take it out, using oven mitts

3) Walk into a dark room containing a table and newspaper

4) Attempt to read newspaper with the skillet

Note: You actually could read it, if you could see in the right part of the infrared spectrum (since all objects in the universe emit electromagnetic radiation at a wavelength inversely proportional to their temperature). Still, this just means that hot objects emit light – not that light and heat are the same thing.

. October 26, 2009 at 8:45 am

Previously:

“The discussion of Wien’s Displacement Law is also quite informative. The law holds that every object in the universe emits electromagnetic radiation, and that the most common frequency exists in relation to that object’s temperature in degrees Kelvin. To go from one to the other, divide 2898 by the temperature in degrees Kelvin. The quotient is the peak wavelength, expressed in microns. Human body temperature is about 310 degrees Kelvin, so our peak electromagnetic wavelength is about 9.35 microns long – in the infrared portion of the electromagnetic (EM) spectrum. Since we are pretty similar in temperature to the surface of the Earth, the wavelengths radiated by the planet are in a nearby portion of the spectrum.”

Tristan October 26, 2009 at 11:41 am

Milan, you really need to take first year logic again.

I wrote “all light is heat”

You said “heat is not light” and provided the evidence that some heat was not light. But some heat is not light is not contrary to the proposition that all light is heat.

All trucks are vehicles. But not all vehicles are trucks. “Try to use a ferrari as a moving van” has the exact same logical content as “try to read a newspaper with a skillet” in this case.

Matt,

“I think it is disingenuous to say that “all light is heat”; it is not…..electromagnetic radiation is not heat. ”

By your account it is “disingenuous” to say that a radiator produces heat. A radiator produces electromagnetic waves at low frequencies which, when they strike things like couches and tables, heat them up. This is exactly the same as light except at different frequencies.

Milan October 26, 2009 at 11:45 am

Not all light is heat. All heat produces some light, but that doesn’t make the two the same.

Certainly, not all heat produces useful light. A pit viper may be able to read a newspaper using a hot skillet, but we cannot.

As such, heat produced by lightbulbs is a wasteful unwanted by-product, at least when houses are not being heated. If we can produce light in ways that generate very little heat (such as LEDs), we are better off.

Milan October 26, 2009 at 11:47 am

A radiator produces electromagnetic waves at low frequencies which, when they strike things like couches and tables, heat them up. This is exactly the same as light except at different frequencies.

As Matt pointed out, the more rapid motion of the molecules in the radiator also bump into adjacent molecules, causing them to speed up. When that happens to air, the subsequent movement of that air causes those faster-moving particles to speed up yet others (conduction and convection).

. October 26, 2009 at 11:50 am

Internal energy
From Wikipedia, the free encyclopedia

In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of atoms within molecules or crystals. It includes the energy in all of the chemical bonds, and the energy of the free, conduction electrons in metals.

Sensible heat
From Wikipedia, the free encyclopedia

Sensible heat is potential energy in the form of thermal energy, or heat, and refers to the heat that is added or removed from the air and dry bulb temperature changes without water vapor content change. The thermal body must have a temperature higher than its surroundings (see also latent heat). The thermal energy can be transported via conduction, convection, radiation or by a combination thereof. The quantity or magnitude of sensible heat is the product of the body’s mass, its specific heat capacity and its temperature above a reference temperature. In many cases the reference temperature is inferred from common knowledge, i.e. “room temperature”.

Tristan October 26, 2009 at 11:52 am

“Not all light is heat. All heat produces some light, but that doesn’t make the two the same.”

This is just backwards. All electromagnetic radiation, when it hits an object, increases the heat of that object (all other variables held equal). But not all electromagnetic radiation is light, most is outside the visible spectrum. (What “light” is is just a product of how our eyes work.)

The point is, of course the most efficient lights are those which only produce electromagnetic radiation in the visible spectrum. But even that electromagnetic radiation can heat up objects. If you are trying to draw the distinction between “is electromagnetic radiation” and “is heat” then you end up in weird loops where you have to say that radiators do not emit heat – although this is what any normal person would say. “This fire is putting out a lot of heat” is a perfectly acceptable use of “heat”. So lights put out heat too, right?

Milan October 26, 2009 at 11:52 am

The proportion of heating that comes from radiation could be approximated by wrapping your radiator in a vacuum chamber that is as transparent as possible to electromagnetic radiation.

Milan October 26, 2009 at 11:54 am

‘Heat’ is how fast molecules are moving. Bombaring molecules with radiation does (usually) make them heat up, but that doesn’t mean that heat and light are the same thing.

Tristan October 26, 2009 at 1:08 pm

Light is radiant energy. We often call radiant energy “heat”, although by your technical definition it is not.

Tristan October 26, 2009 at 1:13 pm

“The proportion of heating that comes from radiation could be approximated by wrapping your radiator in a vacuum chamber that is as transparent as possible to electromagnetic radiation.”

It’s actually much easier. Our hands can tell the difference between radiant heat and hot air. Holding your hand near the radiator and noticing how much it’s being warmed up by a breeze of hot air, and how much it’s being warmed by radiant heat would do the trick.

. October 26, 2009 at 1:26 pm
Milan October 26, 2009 at 1:27 pm

Think how many watts are being wasted running machines to counteract the unwanted heating effect from lighting.

I recall hearing that electricity demand in Ontario also peaks in the summer, for the same reason, but I don’t have easy access to figures that show that.

. October 26, 2009 at 1:30 pm

Ontario, which was historically a winter peaking province, became a summer peaking province during the past five years, with increased use of air conditioners and slow growth of heating loads.”

Matt October 26, 2009 at 1:48 pm

I think a good way of illustrating that radiation is not ‘heat’ is to use the example of an antenna: electromagnetic radiation striking an object, will heat it up, sure, but when it strikes something like an antenna, it will also produce electricity. That doesn’t mean that radiation is electricity. Similarly, it is not heat.

My first post was meant to be informal, people intuitively think of heat as something warm (which it is technically, too) and light as the visible spectrum (less technically true). But if we want to be really technical, it is also wrong to say that radiation is heat. For heat to exist, there needs to be matter.

Tristan October 26, 2009 at 4:22 pm

Again, this is a technical definition of heat which is internally consistent, but which doesn’t correspond to the everyday semantic content of the term. According to this meaning, when I say a fire is “giving off heat”, I’m technically incorrect – a fire is giving off radiation which turns into heat when it hits objects.

This can be perhaps solved by the potency/actuality distinction. A fire gives off potential heat, which becomes actual heat when it collides with matter. So, light is heat of a sort – it is heat potentially.

Milan October 26, 2009 at 4:29 pm

As Matt points out, light can turn into other things. Radio waves get turned into electricity by antennas. Similarly, photovoltaic systems turn light into electricity.

Light can also be converted into kinetic energy (also).

As such, it is as much ‘potential electricity’ and ‘potential motion’ as potential heat.

Milan October 26, 2009 at 4:38 pm

It is also vital to all life on Earth that light is potential chemical bonds.

Tristan October 26, 2009 at 5:00 pm

This conversation reminds me of Chomsky’s criticism of the idea of definitions. I.e. whatever water is, you can’t define it chemically. According to him, the semantic content of words is a complex assemblage that is not reducible, and therefore must be in some sense innate.

Milan October 26, 2009 at 5:04 pm

The question at hand is whether two things are in fact the same thing or not: a question of sets and what belongs in which.

I don’t think the set of things you can legitimately call ‘heat’ includes light, and I don’t think the set of things you can legitimately call ‘light’ includes heat.

It is reasonable to use ‘light’ as shorthand for all electromagnetic radiation, though it isn’t very precise. The most sensible definition of heat seems to be based around how quickly molecules in a material are moving relative to one another.

Milan October 26, 2009 at 5:06 pm

As for water, it seems like an especially easy thing to define: it’s what you get when you have atoms of oxygen, each bonded to two hydrogen atoms, and kept within a certain range of temperatures and pressures.

Tristan October 26, 2009 at 5:16 pm

If you ask for a glass of water, and they bring you tea, you are angry – that isn’t what you asked for.

If a tea filter is installed because it’s a better way of cleaning water than something else, what comes out of the tap is still water. Even if it is chemically identical with the cold tea that a waiter brought you when you asked for water.

Whatever water is, it isn’t a substance.

Milan October 26, 2009 at 5:20 pm

If a tea filter is installed because it’s a better way of cleaning water than something else, what comes out of the tap is still water.

No it isn’t. The water before going through the filter must already be impure, if it requires filtering. While what you get after the filtering might be closer to pure water than what you started with, it still isn’t pure water.

The issue here is how pure water needs to be in order for us to describe it as ‘water’ and not something else. There isn’t an absolute standard for that, since it depends on perception and what you want to use the water for. Nonetheless, water is a substance that can be more or less pure.

. October 26, 2009 at 5:22 pm

Vienna Standard Mean Ocean Water
From Wikipedia, the free encyclopedia

VSMOW, or Vienna Standard Mean Ocean Water, is an isotopic water standard defined in 1968 by the International Atomic Energy Agency. Despite the misleading phrase “ocean water”, VSMOW refers to pure water (H2O) and does not include any salt or other substances usually found in seawater. VSMOW serves as a reference standard for comparing hydrogen and oxygen isotope ratios, mostly in water samples. Very pure, distilled VSMOW water is also used for making high accuracy measurement of water’s physical properties and for defining laboratory standards since it is considered to be representative of “average ocean water”, in effect representing the water content of Earth.

Milan October 26, 2009 at 5:27 pm

As demonstrated by the VSMOW standard, isotopic ratios are a problem when it comes to defining water. Clearly, water needs to consist of H20. It isn’t clear whether there is a similarly authoratative ratio of hydrogen-to-deuterium-to-tritium, nor of Oxygen 16-to-Oxygen 17-to-Oxygen 18. You could come up with some possibilities, such as the mean ratio on Earth or in the universe, but it isn’t clear why one would be more correct than another.

Milan October 26, 2009 at 5:32 pm

Perhaps ‘water’ includes all possible isotopic ratios, and is thus a category rather than a thing. Things included in the category would be VSMOW, ‘heavy water’ defined in various ways, etc.

Tristan October 26, 2009 at 5:56 pm

“The water before going through the filter must already be impure, if it requires filtering. While what you get after the filtering might be closer to pure water than what you started with, it still isn’t pure water.”

You seriously mis understanding what filtering is for. It is not for making water closer to H20, but for making it safer for human consumption. Adding chlorine to water might make it potable, and does not make it any less “water”.

Another example, if in Vancouver there was a drink called “Bloob” which was sulfer flavoured water, and it was packaged as a coke product, it would not be “water”. If you asked for a bottle of water and you were given a bottle of bloob, you would be angry.

However, if bloob is chemically identical to the sulfur-rich tap water that you get in Los Angeles, and I bring back a bottle of water from Los Angeles, and someone asks me for water and I give them this, then it is water. Even if it is chemically identical to bloob, it is water.

Milan October 26, 2009 at 7:09 pm

The general category ‘water’ includes both specific varieties of water that are precisely defined (such as) and sub-categories like ‘potable water,’ ‘chlorinated water,’ etc. These categories can be defined by content (salt water) or origin (rain water) and possibly in other ways.

There is the question of when something crosses a threshold into not being water: how much dirt before it becomes mud? How much exposure to Camellia sinensis before it becomes tea? These don’t really strike me as important philosophical questions, however. ‘Water’ is clearly the unadulterated substance. What we are willing to call water in any particular circumstance is a matter of practicality, dependent on our purpose. Chlorinated water might be preferable for drinking, but could be useless for some types of reactions, for instance.

Anyhow, none of this really has much to do with LED lighting.

Milan October 26, 2009 at 7:10 pm

You seriously mis understanding what filtering is for. It is not for making water closer to H20, but for making it safer for human consumption. Adding chlorine to water might make it potable, and does not make it any less “water”.

Adding chlorine cannot really be accurately referred to as filtering. Filtering is for making whatever liquid you are working with more like pure water.

Tristan October 26, 2009 at 9:24 pm

So, “filter coffee” doesn’t exist then? Or, you couldn’t brew tea through a filter?

Clearly, filter doesn’t mean “take something and make it more pure”.

Also, why does water need to mean something which never exists? Why can’t I drink a glass of water? Why does “water” in its everyday usage have to be some strange derivation from something we can know scientifically but never encounter?

Milan October 26, 2009 at 10:00 pm

What do coffee and tea filters do? Remove unwanted impurities: coffee grounds and tea leaves.

Tristan October 26, 2009 at 11:51 pm

Wait a minute here – back to the topic. Blue Harzard? What’s this? There is some information here:

http://www.mdsupport.org/library/hazard.html#blue

So, it looks like I was right to be wary of non-incandescent bulbs, but my fears only apply to some non-incandescent bulbs.

Matt October 26, 2009 at 11:59 pm

Going back to lighting: The way an incandescent light works is by passing an electric current through a filament. The electrical resistance of the filament causes it to heat up. The heat of the filament causes it to irradiate light via incandescence, the filament is literally white hot. Sticking an iron in the fire and having it come out red is the same phenomenon, likewise so is a glowing red stove element.

A fluorescent tube has two filaments on either end that also pass an electric current which cause both to heat and incandesce. Once the tube is sufficiently warm, the circuitry of the fixture stops the current flowing through each filament and starts passing the current between the filaments on either end. The electric current passing through the gas in the tube causes it to fluoresce. [Boring part: the electricity excites the atoms of the gas forcing some of their electrons into higher energy orbitals. When an electron spontaneously returns to a lower energy orbital, a photon is released]. Here is where the energy is saved. Rather than chiefly producing heat (note radiation has nothing to do with how I mean heat), the electricity is used to produce light.

So why do fluorescent bulbs still get warm? Partly still because of electrical resistance, but also partly because they absorb non visible wavelengths (they are coated to prevent dangerous UV from escaping, and they also absorb some IR) and convert them to heat.

Milan October 27, 2009 at 12:22 am

I find it perplexing when people focus on undemonstrated hypothetical harms (what if discrete spectrum lighting has subtle negative psychological consequences?) at the expense of the exceedingly well demonstrated threat of climate change, as well as the proven consequences of air pollution from fossil fuel power.

Tristan October 27, 2009 at 12:38 am

Well, you shouldn’t find it perplexing. It’s totally normal that people would concentrate on harms that will happen to them specifically rather than harms that will happen to everyone. That’s part of our totally individualized modern late capitalist de-politicized debt-driven culture.

Milan October 27, 2009 at 8:35 am

Is blaming culture not a way of avoiding responsibility?

Tristan October 27, 2009 at 9:28 am

That comment doesn’t even make any sense. Not being surprised by something because it is normal in our current culture doesn’t have anything to do with personal responsibility, or our responsibility to shift culture.

Can you “blame” culture for things? Culture isn’t a moral actor. The word “blame” as a moral meaning only when applied to moral actors. So “Blaming culture….avoiding responsibility” is using the word “blame” equivocally.

Milan October 27, 2009 at 9:40 am

People often blame culture, when they act immorally but in a way that is common at the time. Slavery at one point is an example, as are female genital mutilation and excessive greenhouse gas emissions today.

Ultimately, achieving change depends on people no longer hiding behind the practices of others, and taking responsibility for what they do themselves.

Tristan October 27, 2009 at 1:12 pm

Pointing out why you shouldn’t be surprised is not the same as evading responsibility. It could be argued to be irresponsible to not make oneself aware of the social reality such that one is surprised when pre-dictable things happen. If you want to change things, you’ve got to know how things work.

Milan October 27, 2009 at 1:42 pm

Though pointing out that the way they work doesn’t make sense is an important part of the push to change them.

. November 3, 2009 at 3:40 pm

With over eight kilowatts of lighting capacity in his home, your correspondent decided three years ago to replace each incandescent light bulb, when it died, with a CFL equivalent. It has been a costly exercise. The average saving is supposed to be around $30 for each incandescent replaced by a CFL, over the latter’s supposed lifetime of 10,000 hours. But such savings quickly vanish if a CFL dies sooner than expected, which earlier ones routinely did.

These premature deaths were usually caused by a failure of the CFL’s electronic ballast. This is a small circuit board in the base of the bulb that uses a rectifier, a capacitor and a pair of transistors to produce a steady, high-frequency voltage that stabilises the current which passes through the mercury vapour in the tube. Excited by the current, the mercury atoms emit ultraviolet light, which bombards the phosphor coating on the inside of the tube. It is the phosphor coating, not the mercury vapour itself, that produces the fluorescence effect—and hence the visible light. The ballast is there simply to reduce the lamp’s start-up time and to eliminate flickering.

Unfortunately, the resonant circuitry in the ballast does not take kindly to having its input voltage varied. That is what happens when a CFL is plugged into a socket with a dimmer attached. Also, switching a CFL on and off repeatedly has a similar effect. No surprise, then, that household lights which are used frequently but briefly will burn CFLs out in hundreds rather than thousands of hours. For that reason, your correspondent has now stopped using them in bathrooms and walk-in closets.

He has also found that CFLs last longer when used upright in a lamp-stand, rather than dangling from a ceiling fixture. The worst place for them seems to be in concealed fittings in the ceiling, where there is little ventilation. While it is true that CFLs generate far less heat than incandescent bulbs (hence their five-fold increase in efficiency), they still get pretty hot. If not ventilated properly, their ballast circuitry can get fried enough to fail.

Still, there is no denying that, on most other counts, CFLs are a far better choice than incandescents. They consume a fifth the juice, generally last five to ten times longer, and now cost only twice as much. Over its lifetime, claims the United States Environmental Protection Agency, a CFL saves 2,000 times its own weight in greenhouse gases.

. December 1, 2009 at 8:45 am

Lifecycle Energy Costs of LED, CFL Bulbs Calculated

“The NY Times is reporting on a new study from Osram, a German lighting manufacturer, which has calculated the total lifecycle energy costs of three lightbulb technologies and found that both LEDs and CFLs use approximately 20% of the energy of incandescents over their lifetimes. While it is well known that the newer lighting technologies use a fraction of the energy of incandescents to produce the same amount of light, it has not been proven whether higher manufacturing energy costs kept the new lighting from offering a net gain. The study found that the manufacturing and distribution energy costs of all lightbulb technologies are only about 2% of their total lifetime energy cost — a tiny fraction of the energy used to produce light.” The study uses the assumption that LEDs last 2.5 times longer than CFLs, and 25 times longer than incandescents.”

. December 18, 2009 at 10:22 am

LED traffic lights don’t melt snow

Cities that installed LED traffic lights to save money are learning that the incandescent lights they got rid of had a useful purpose: their waste heat melted the snow that covered them in winter storms.

Municipalities around the country are taking different steps to keep their signals shining brightly in the face of Mother Nature. Crews in St. Paul, Minnesota, use compressed air to keep their lights clean. In Green Bay, Wisconsin, city workers brush the snow off by hand in a labor-intensive process.

. March 5, 2010 at 5:34 pm

Graham’s law — In physics, a gas law which states that the average kinetic energy of the molecules of two samples of different gases at the same temperature is identical. It is named for Thomas Graham (1805–1869), who formulated it.

. March 9, 2010 at 12:26 pm

Get ready to replace your light bulbs

Welland, Ont. — Globe and Mail Update Published on Tuesday, Mar. 09, 2010 7:48AM EST Last updated on Tuesday, Mar. 09, 2010 11:57AM EST

For decades, lighting was a business where nothing much happened.

Incandescent bulbs, invented in the horse-and-buggy age more than a century ago, were used in homes, while fluorescents, a technology of 1930s vintage, dominated in stores and offices.

But with the imminent death by government decree of the energy-hogging incandescent bulb, the lighting industry has become a surprise area of innovation.

CRS Electronics, based in Welland, Ont., is hoping it’s on to the next big thing: the commercialization of a long-lasting, energy-sipping light bulb. The company is betting that light-emitting diodes (LEDs) represent the future. “It’s just clear as a bell. This is going to take over,” predicts Scott Riesebosch, an electrical engineer who is president and founder.

CRS is the quintessential small company with big dreams. Even though it is a tiny player compared with lighting behemoths such as GE or Philips, it has developed what experts contend is the best LED on the market for replacing two-pronged halogen light bulbs.

. March 14, 2010 at 7:01 pm

Technology Quarterly

Quantum dots
A quantum leap for lighting
Consumer electronics: Tiny semiconductor crystals, called quantum dots, enable new forms of energy-efficient lighting

Mar 4th 2010 | From The Economist print edition

“Quantum dots are tiny crystals of semiconducting material just a few tens of atoms, or a few nanometres (billionths of a metre), across. They are typically made using some combination of zinc, cadmium, selenium and sulphur atoms. Their origins go back to work published in 1983 by Louis Brus, then at Bell Labs, in New Jersey, though it was several years before another physicist, Mark Reed at Yale University, described these tiny semiconductor clumps as “quantum dots”. When excited by light or electricity, a quantum dot emits light of a colour determined by the dot’s size and the material from which it is made. Light of a particular colour can therefore be produced by exciting dots of a specific size.

This approach has two advantages over using a YAG phosphor: with the right combination of quantum dots, the resulting light can be tuned to be much warmer; and quantum dots convert blue light to white light with an efficiency approaching 100%, so less energy is needed to produce a given amount of white light. The bulb (shown above) will go on sale this year. It will offer the performance of a 70-watt incandescent bulb but will draw only 11 watts. (A comparable CFL bulb would draw around 15 watts.)”

. March 25, 2012 at 1:47 pm

Briam Lam figured out the best LED lightbulb, and explains why it will eventually pay for itself: “They’ll last 15-25 years compared to about a year for regular bulbs [and] 1/5th of the power … so they can eventually save you hundreds of dollars.

Leave a Comment

You can use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Previous post:

Next post: