Toddlers with Lasers

My only real New Year’s resolution this year: restart the blog and post by the end of January. Well, it’s Groundhog’s Day. Better late than never?

I am back at work these days doing some engineering work for a local company, which is one of the reasons that I have let the blog slide, though I’ve missed this. A little while ago, my daughter wanted to pretend that one of her Little People was me and was driving around in a car, stopping to get gas and going to work. This is apparently what I do. She wanted to pretend that the Little Person was at my work so I decided to show her what I do at work.

Okay, most of what I do at work involves staring at a computer and would be pretty boring for a two year old. But, I do have some educational optics kits that are used to teach students about light so I went out to the garage and brought it in.

The result was amazing. Almost 30 minutes (an eternity to a two year old) of exploration.

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The kit consists of a laser source that shoots out 5 laser beams. These represent ‘rays’ of light. The idea is for students to then take some of the pieces of clear plastic that are molded into different shapes and see how the light travels through them. There are positive and negative lenses that bend light toward and away from their centers and blocks of glass for investigating.

Here is an example of a positive lens that my daughter put in the path of the light.

The main concept here is that when light hits something like glass or plastic, some it reflects off and some of it bends and travels through. How much reflects and how much travels through, as well as how much it bends, depends on the material. Mirrors reflect almost all the light, but glass only reflects a little and the rest travels through (making it a good window material!).

Here is a basic artistic view of what happens when the light hits a piece of glass:

If light inside the glass hits the surface with the air at a large enough angle, all the light will be reflected and none of it will be transmitted back into the air. This is called total internal reflection and can be used to make mirrors or trap light in things like fiber optics (that’s what brings my internet to my new house but more on that later).

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At one point, my daughter put a prism in the light at just the right angle so that a little traveled through (and bent a lot) and a lot of the light was reflected. She put the prism down and then said, “Whoa mommy!” Whoa, indeed. Total internal reflection is cool.

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Optics is cool, but I thought the best part of this experience was her exploration. Unlike my college students, she did not know what she was ‘supposed to do’ and did not care anyway. She tried putting all her toys in the laser beam – most of which did nothing at all but that did not phase her. She would just try something else – plastic Little People (every single one of them), Legos, teddy bears, books, and once she tried a little piece of foam packing material that turned about to be the coolest thing. The light bounced around the little piece of foam and it glowed bright red. She was so happy!

Her wonder gives me so much joy.

If you’re interested in the kit itself, I bought it at Arbor Scientific. You can find them there for $99. It is pretty basic but is a lot cheaper and in many ways just as good as the more expensive educational kits.

Curiosity

A few weeks ago, when the first news on the Higgs boson came out, a friend of mine sent me an email requesting that I write a blog entry explaining what it’s all about (that blog entry will be coming next week on Laser Mom). He said that understanding this part of physics was hard for him as an engineer since he did not have much background in modern physics. He also asked,  “Why do we care about what gives us our mass?”

His question made me think about research in general. Of course, as scientists and engineers, we all write proposals to get funding, and papers for scientific journals, and give conference talks, and spend quite a bit of time explaining why what we do is useful and will save the world and make us all rich someday. But really, why do we really do our research? I think that most us can honestly say (hopefully!) that we do it because it’s really cool. It’s fun. Why do we want to find out what gives us our mass? Because we can. We are curious and want to understand how things work and what new things we can accomplish.

One of the things that I have done in the recent past for research is to shine laser beams into glass or polymers (i.e. plastic) and see what happens. It turns out you can use the energy in the laser beam to change the properties of the materials for practical engineering reasons – creating small feature sizes so that we can have better, faster, smaller computers and to write optical waveguides so that we can send information (internet) easier and faster from place to place. But I did not really study this just for practical reasons – it’s just fun! (The practical reasons are, of course, important to get funding to get paid to do what I love.)

I have to wonder if the first scientists to write optical wires in glass with high power lasers were not thinking (at least a little bit), “This laser is so cool. I wonder what would happen if we focused it down into that piece of glass? Will the glass vaporize? Let’s try it!” (I believe Davis et al. were the first to publish on this topic.)

Perhaps they were much more organized and focused in their pursuits, but I have to admit that most of the interesting things I have accomplished in the lab have started out with, “I wonder what would happen if…”

My one year old daughter is a natural experimentalist. She loves to try out new things and do things just to see what happens. If I drop this, what will happen? What if I pull on this handle? What will happen if I pull myself off of this landing (Ow!)? It is amazing to see how quickly she learns new things just by exploring and trying everything that comes to mind.

We have all (hopefully) mastered the basics of gravity at this point, but our curiosity and desire to try out new things is what makes us good scientists. Shining a laser beam into a light sensitive polymer and watching what happens just fascinates me. There are so many interesting things going on, from basic light propagation in glass/plastic to chemical reactions in the material.

Then there are a the cool things you do when you put two laser beams together – using different colored laser beams of different shapes to activate different chemicals in a material and making super tiny little dots in the material. There were three papers in Science a few years ago (May 15 2009 issue) discussing different ways of combining optics and chemistry to create features that were smaller than anything you could do before with these lasers (By the way, you can get all three of those papers for free if you sign up on the Science website.)

Oh sure, there are lots of good practical applications of shining lasers into materials (faster internet and computers?) and those are probably the things I will tell you if you ask me to give a talk on this research and certainly what I will tell you if I need to write a grant proposal.

But why do I really work with lasers, shine them into materials, use them for microscopy? Why are the scientists at CERN looking for the Higgs Boson?

I think the Mars rover’s name covers it: Curiosity.  Anyone who watched the video of Curiosity’s landing (YouTube – watch between minutes 5 and 6) can see the excitement and joy that scientists and engineers get when they have successfully completed a mission, discovered a new particle, built a new gadget or made measurements that no one before them has ever been able to do.

As scientists and engineers, we are a curious folk. Sometimes we get so wrapped up in funding, papers, etc. that we forget why we do what we do. That’s one of the reasons I am excited to go to an optics conference this fall. Conferences are a great opportunity to explore and enjoy that curiosity. We can go to talks outside our field, talk to other scientists we have never met, and get outside our normal routine. This setting always re-energizes me and gives me lots of new ideas of things I would like to explore when I get back to the lab.

Of course, with an infant at home, I do not really need to go anywhere. Babies are natural experimentalists and seeing her intense concentration in trying something new and her joy at discovering new things reminds me every day why science is so cool. We are all born curious, and hopefully we keep that curiosity as we grow older though we each tend to focus it in different directions.

Lightning Strikes

I was on vacation with my family last week and did not quite manage to get this entry up on time and so missed last week. But I enjoyed the time spent with my family, visiting and traveling to new places.

There have been a lot of fires in CO this year. The dry winter, dry spring and very hot, dry and windy summer weather have made for perfect conditions for fires to spread rapidly in the forested areas of the mountains. Because of this, there is an extreme fire ban in CO to prevent more fires. This was the quietest 4th of July I can remember because many of the towns around where I live cancelled the fireworks celebrations. No one wanted to start another fire.

Unfortunately, mother nature has not been informed of the fire ban. Many of the fires this year were started by lightning strikes during one of our many dry thunderstorms – lots of lightning and thunder and little or no rain.

A few weeks ago, I went out for a walk with my daughter and looked up to see a huge plume of smoke in the sky. I immediately looked up the news to try to figure out where the fire was – not close enough to be a danger to us (other than the horrible smoke) but close enough to affect many of my friends. In the news article, it stated that the fire was probably started by lightning as 51 lightning strikes had been detected in the area.

51? Really? The curious geek in me forgot all about the fire and started to wonder how they could possible know that. I spent some time looking into lightning detectors. There are several different types, but this article mentioned ground detectors, so I wanted to know how those work.

Lightning is really cool, and of course, a little scary too. But I have always been mesmerized by watching lightning flashes on a stormy day. In order to understand how ground detectors measure lightning, let’s first think about why we can see lightning – what is causing that huge bright flash?

Lightning is caused by huge static discharges. In an electrical storm, there is a huge charge difference between the clouds and the ground. This sets up a very large electric field across the air. This basically means that there is a huge amount of energy stored that has the potential to affect the air around it.

If the charge stored is enough, the electric field starts to ionize the air around it. This means that the strong electric field can actually tear electrons off of the atoms in the air. These electrons then become free to move around (no longer tightly attached to the atoms) and this causes a current to flow through the air like it would through a metal wire. (How Stuff Works: Lightning).

Very cool! And sort of scary…something powerful enough to rip atoms apart certainly is going to do a lot of damage if it hits me!

As this energy moves through the air, this electrical energy and atom ionization emits electromagnetic radiation – light. So we see a bright flash of light. You can see a pretty picture of the lighting and its spectrum (what colors are contained in this white light) here.

The lightning also emits a characteristic lower frequency electromagnetic radiation. In order to detect the lightning, antennas are set up to detect this lower frequency radiation. For cloud-to-ground detection, a set of three antennas are set up to triangulate the signal. All three antennas will detect the signal from the lightning and by measuring the time it takes to reach each antenna, the location of the lightning strike can be determined. Visible light detection (the big bright flash!) is also used to make sure that the lower frequency radiation is really coming from lightning and not some other source. (Wikipedia)

I never knew that these types of detectors were set up around us. I think it’s really cool that lightning detectors work so well. You can even make your own basic lightning detector if you like home electronics projects.

Despite the high level of technology and engineering that goes into really effective lightning detectors, I must admit that I am still more in awe of the amazing photographers out there that can take beautiful pictures like this (Wikipedia Commons):

During our vacation, we landed twice very near a thunderstorm. Despite being quite exhausted from travel and delays with an infant, I was in awe of the beauty and power of the lightning viewed from the sky. It is an amazing thing.

Fortunately, the weather has improved since the worst of the fires in CO. While it is still dry here, daily thunderstorms have brought some rain to help things from getting too dry. Of course, these storms also tend to bring lightning. Hopefully the wetter conditions will prevent more fires, but it is still important to be careful in the late afternoons, especially in the mountains. Lightning is beautiful but also quite powerful and dangerous.

Undergraduates and the Future of Optics

The past week or so has been busier and more exhausting than usual (with a little girl who is suddenly having trouble getting to sleep), so I missed the blog last week. My daughter’s ability to sit up and stand easily is causing her all sorts of trouble. Whenever we lay her down in her crib, she thinks she should immediately stand up and walk around her crib (still holding onto the side). She is, of course, exhausted and needs a nap but can not quite figure out that she needs to lie back down in order to sleep. Poor kid (and poor parents!).

Having found some time to myself again after a few long weeks, I decided to do some more exploring on the Frontiers in Optics website. While the full conference program will not be up for some time, there are tons of exciting invited speakers and special symposia listed for the conference. I am going to have a hard time deciding what things to go to with so much going on – one of the big challenges of the big conferences with so many concurrent sessions.

Two of the special symposia struck me as being really interesting and related: The Future of Optics: A Perspective at Emil Wolf’s 90th Birthday and the Laser Science Symposium on Undergraduate Research.

The Future of Optics Symposium is going to address the future of optics in the areas where Emil Wolf contributed the most – Inverse Problems, Coherence and Quantum Optics, Physical Optics, and Optics at the University of Rochester.

I am especially interested to hear Anthony Devaney’s talk about the Future of Inverse Problems since this relates directly to my own research in Optical Diffraction Tomography. While there are a lot of exciting areas of research dealing with new technologies in lasers, fabrication, and nanotechnology, I am always fascinated by how much there is left to learn and investigate in the very fundamental problems of optical scattering and propagation. Being able to measure the intensity profile of light after it has passed through an object and then reconstruct that object allows us to image objects that standard microscopes cannot see. And, of course, as we learn to make smaller and more complicated structures, we need ways to measure them.

This symposium seems like a wonderful way to honor a great scientist and get the younger generation excited about the exciting research that is coming up in these fields. And, speaking of the younger generation, there is another special symposium just for them: The Symposium on Undergraduate Research.

I only found out about this symposium a couple of years ago, though it has been going on for 12 years now. This is an opportunity for undergraduates to come and be involved in a large and vibrant conference. If you are an undergraduate (or have undergraduates in your lab), you should definitely look into this.

The organizer is Hal Metcalf from Stony Brook University and the deadlines for submission are at the end of the summer (instead of May) to accommodate undergraduates who usually do the bulk of their research in the summer. The symposium consists of oral presentations and post talks and the quality is really amazing – many of these presentations could easily have been given in the main conference sessions and no one would have thought they were undergraduates.

I had three students who worked with me present at this symposium in 2010 and they could not stop raving about what a wonderful experience it was. Two of my students had not planned on pursuing optics after graduation, but were so excited by the experience that one is now a graduate student in optics and the other is planning on applying for optics programs this fall.

I feel like a walking advertisement for this symposium, but I just think it is such a fantastic opportunity for undergraduates to be introduced to the vibrant optics research community. Especially for students in smaller departments who do not normally have access to these sorts of opportunities. And, of course, it is a great place for graduate advisors to recruit really phenomenal future graduate students.

Being very education and student-oriented, I think it is really cool that in addition to talking about all the current (and exciting!) research, part of Frontiers in Optics is devoted to looking toward the future of research – both in specific topics and in supporting and engaging the future scientists who will be the ones to engage in these topics.

The Conclusion to the Great Nightlight Mystery

Three weeks ago, we embarked on the Great Nightlight Mystery: Why does my daughter’s nightlight turn off in sunlight, but not when I turn on the overhead light?

First, we looked into how a spectroscope works so that we could investigate the different spectra of the lights in my house. We discovered that incandescent light bulbs contained all of the colors of the rainbow, much like the sunlight that comes through my windows. This is because sunlight and incandescent bulbs are both examples of blackbody radiation. The fluorescent bulbs, on the other hand, were only made up of a few colors of the rainbow, through when combined, the light still looks white. Finally, we looked into how the LED nightlight itself works and what colors of light is puts out.

So where does all this leave us? Let’s look at a summary of the spectra, or color outputs, of the different lights in my house:

The nightlight must have a photodetector – this is usually a semiconductor material that detects light. Just like the materials that emit light of only certain colors, this photodetector can be designed to only detect light of certain colors. My theory (I don’t know for sure) is that the detector was picked so that it would not detect light from the LED nightlight. It would then only be affected by outside light.

We checked this – our external bright LED light did not seem to affect the nightlight (turn it off) unless the nightlight was very close to the LED light bulb. The same is true for the fluorescent bulbs. However, a small amount of incandescent light or sunlight will turn the nightlight off.

Looking at the spectra above, it’s difficult to see why this is. I thought originally that the dip in light from the LED – the 500 nm blue region must be the light that the detector is sensitive to. However, the fluorescent bulb has light there. Perhaps the detector is sensitive to light in the bluish-green – that narrow area where neither the LED or fluorescent bulb emit light? I would need more information on the detector or some more sophisticated equipment than I have in my house to be sure.

The detector does seem to be wavelength dependent, though. It seems to be a poor design to me that it does not turn off in the presence of fluorescent light bulbs since many homes are switching over to fluorescent bulbs as a more efficient alternative to incandescent bulbs. In fact, there are new standards in the US designed to help phase out the inefficient high wattage incandescent bulbs. You can read more here. Since many of the more efficient light bulbs are compact fluorescents or LED light bulbs, my daughter’s nightlight will not be very useful in most houses – it will always remain on. Of course, if I open the shades, the sunlight will turn it off. I suppose the most efficient lighting will always be sunlight anyway, especially in very sunny Colorado.

What does this mean for you and your house lights? You will need to make choices between brightness, color, efficiency and cost. Sunlight and incandescent bulbs are probably easiest on your eyes, but new, better compact fluorescent bulbs and LEDs have better spectra and are much more efficient. Here are a couple of things to keep in mind:

  • BRIGHTNESS: We are used to thinking of brightness in Watts, but really that has nothing to do with brightness. The Watts are just a measure of how much power is required to run a traditional incandescent bulb. The unit of measurement ‘lumens’ is a more appropriate measurement of brightness. The Department of Energy provides the following graph to help you convert between the two:

  • COLOR: The new lighting label on the left above also includes a section entitled “Light Appearance.” This compares the light output to the light output of a blackbody of a certain temperature. If you remember from our discussion of blackbody radiation, a higher temperature means light that is more blue and less red. From the PhET simulation website on blackbody radiation, we see that the temperature of a typical incandescent is about 3000 K, and sunlight is approximately 5700 K. This can help you find a bulb that is more red (warm according to the label) or more blue (cool on the label) depending on what you prefer.

Of course, as we can see with our little handheld spectrometer, none of the lights are quite as good as just opening the shades on a sunny day – that has the best color and uses the least energy, but it is not always an option (especially at night!).

  • EFFICIENCY & COST: The new lighting label also includes an estimated yearly energy cost and lifetime. With that and the cost of the light bulb, you can figure out which light bulbs are most cost efficient. Of course, if saving energy is more important to you than saving money, you may just go with the most efficient option.

Hopefully you enjoyed our light filled April and now feel confident in your knowledge of light bulbs. I at least better understand my daughter’s nightlight and realize that if I want it to turn it off with the room lights on, I had better get an incandescent light bulb, open the shades or possibly explore different compact fluorescent and LED light bulbs until I find ones with the appropriate color spectrum.

The Great Nightlight Mystery, Part IV: Light Emitting Diodes (LEDs)

Two weeks ago, we embarked on the Great Nightlight Mystery: Why does my daughter’s nightlight turn off in sunlight, but not when I turn on the overhead light?

First, we looked into how a spectroscope works so that we could investigate the different spectra of the lights in my house. We discovered that incandescent light bulbs contained all of the colors of the rainbow, much like the sunlight that comes through my windows. This is because sunlight and incandescent bulbs are both examples of blackbody radiation. The fluorescent bulbs were only made up of a few colors of the rainbow, though when combined, the light still looked white.

This week, we are going to look into how Light Emitting Diodes (LEDs) are different (and similar) to the other types of bulbs in my house. With this information, we should be able to not only solve the Great Nightlight Mystery, but also understand why our eyes and our wallets prefer certain types of light bulbs.

If you recall from last week, fluorescent bulbs contain a gas of molecules that glow at very specific colors due to the molecule’s changing energy levels after a high voltage is applied. LEDs work on a very similar concept. They are solids, though, so the molecules work together instead of independently like they do in a gas. This causes some differences in the output light.

The atoms in semiconductors (the materials out of which LEDs are made) are in very close proximity and work together to form bands of energy. LEDs are formed by putting two semiconductors in close proximity, one that has an excess of electrons (negatively charged particles) in a higher energy band, and one that has an excess of positive charge, or holes where the electrons can fall into, in a lower energy band. Putting these materials together and applying a current causes the electrons in the higher energy band to fall into the lower energy band. Just like in the fluorescent bulbs, the excess energy is emitted in the form of light. The color, or frequency, f, of this light is directly proportional to the energy difference between the higher and lower energy bands:

The higher the energy difference, the higher the frequency, or the more blue the light that is emitted looks. The energy bands are wider in solids than in atoms, so the light emitted has a larger bandwidth – this means that a wider range of colors is emitted, but they are still very narrow band compared to sunlight.

You have probably seen quite a few LEDs as lights on electronics. They are most commonly green, blue, or red. But the LED nightlight in my house appears to emit white light. If an LED can only emit a single band of color, how do they make white LEDs?

I read an article recently in Optics and Photonics News that discusses the various ways of making good white LEDs and talks about whether or not LED lights are ready to take over the light bulb industry (Jeff Hecht, “Changing the Lights: Are LEDs Ready to Become the Market Standard?”, Optics and Photonics News, 23 (March 2012).).

From this article, I learned that one way to make a white LED is to combine three colored LED’s – red, green and blue – so that the result looks white. It is generally less expensive and more efficient, though, to use a single blue LED and a phosphor. The LED emits light at 460 nm (blue light). This light then hits a phosphor. The energy from the light excites the phosphor to a higher energy level (yes, just like the atoms in fluorescent bulbs and the materials in the LEDs) and then atoms then fall to a lower energy level and emit light. The phosphors used in white LEDs generally emit light over a fairly broad range, from about 500 to 700 nm. The white LEDs use the very energy efficient LEDs in the blue to provide the energy (and blue light) to then get the longer wavelength light from the phosphor. The resulting spectrum looks something like this (from Wikimedia Commons):


This graph shows a big peak of intensity at 460 nm due to the blue LED (made of gallium nitride (GaN) or indium gallium nitride (InGaN) in this case – those are the semiconductor materials that make up the LED). There is also a smaller, wider peak of light covering the other visible wavelengths from the cerium doped yttrium aluminum garnet phosphor (Ce:YAG).

There are a couple of interesting qualities of LEDs that we can figure out from this graph. First, they emit a lot of blue light, so they look pretty blue. There is also a dip of little light in the blue-green (around 500 nm) so they do not emit much light there.

Using different phosphors, or multiple phosphors can change the output light to make it look more like incandescent bulbs, which emit more red light and less blue light. Bulbs with better color outputs can be less efficient, though (information from Wikipedia).

I used my spectrometer to look at my LED nightlight and another LED light bulb that we bought because we were curious. Here is the picture of the spectrum (note the blue is on the right in this picture unlike the graph above):

We can see the bright blue on the right from the LED, then the dip in light between the blue and green, then the broad green-yellow-orange-red light from the fluorescing phosphor. Just like we expected. Cool!

LEDs are very energy efficient – more so than both incandescent bulbs and fluorescent bulbs, but they are also still fairly expensive to buy in the store, so it will cost quite a bit to replace all the bulbs in the house.

Now that we understand all the light sources in the house, we can figure out why my daughter’s nightlight turns off in sunlight but not in room lights. Coming up next…

The Great Nightlight Mystery, Part III: Fluorescent Bulbs

Two weeks ago, we started on the Great Nightlight Mystery: Why does my daughter’s nightlight turn off in sunlight, but not when I turn on the overhead light?

The first week, we looked into how a spectroscope works – how I measure the colors that makes up the various lights around my house. Then, last week, we looked into why sunlight is made up of all the colors of the rainbow and how incandescent light bulbs are similar (and different) from sunlight.

But we still have to tackle the mystery of my kitchen light, which showed a very different spectrum:

It contains only a few discrete colors of the rainbow, not all of them. Why?

My kitchen light is a fluorescent light bulb. Instead of having a thin metal filament that is heated until it glows, fluorescent bulbs consist of tubes that are filled with gas of a very particular type of molecule. A large voltage is applied across the gas tube and this causes the tube to glow. Why does it glow and why only at certain wavelengths, or colors?

Let’s take a little side trip into what atoms are made of and how they work. We’ll pretend there is Hydrogen in the tube since it is the simplest atom to think about. Physicists always like to simplify a problem as much as possible and then extend the results to other situations. It’s really because we’re lazy, but Shhhh! Don’t tell anyone. Fluorescent bulbs are not filled with Hydrogen, but different types of atoms and molecules act much the same way, at least in this situation.

Atoms are generally made up of a nucleus, which contains protons and neutrons. Just one proton for Hydrogen. Around this nucleus are electrons that orbit the nucleus. It’s more complicated than that, but this is a good approximation. Again, Hydrogen only has one electron. You can see why I chose this one? Lazy, lazy, lazy…

So here’s the really strange part: Electrons can only orbit the nucleus at certain distances with certain energies. This is really weird. We can drive our cars at any speed, right? It would be weird if we could only drive at 5 mph, 10 mph, 15 mph, etc., right? Or if I could only heat my coffee up to 150°F or 250°F and nothing in between? (This would be especially tragic since the National Coffee Association states that coffee should be brewed at about 200°F.)

When we start looking at things on a smaller and smaller scale, like electrons and atoms, there are rules that apply to the energies that particles can have. Here’s a rough picture of that means for an atom:

The electron can orbit the atom on any of the green lines, but cannot ever be anywhere. This may bother some of you – how can it get from one orbit to another without ever being between them? Quantum mechanics can sometimes make you dizzy. It is best not to think too much about it.

So there are a lot of these little atoms floating around in a glass tube in my fluorescent light bulb. I apply a high voltage across the gas. The electrons are attracted to the positive side of the voltage and this gives them energy to move. They tend to move away from their nucleus into a higher orbit. But electrons, like most of us, don’t like to spin around at high speeds and prefer to relax after a while, and so they drop back down to a lower orbit closer to their nucleus. Now they have less energy, and that extra energy that they gave up had to go somewhere. It can go into a photon – a bundle of light that leaves the atom.

The energy in a photon is directly related to its frequency, or color. The higher the frequency, the higher the energy. You may remember that blue light has a higher frequency than red light, so blue photons have more energy than red photons.

When an electron moves from one orbit to another, it changes energy by a very specific amount and so it gives off light of a very specific color. Since electrons can only exist and move between specific orbits, when they move around, they only give off very specific wavelengths of light.

So how does this light bulb work? It applies a big voltage to give electrons energy to move them up to orbits further from their nuclei. They get tired (yes, I am anthropomorphizing here and giving electrons human characteristics they likely do not have) and relax to a lower orbit, giving off a photon of a specific color. If I have lots and lots of the same type of atom, then the atoms will glow only at certain specific colors. What colors these are depends on what type of atoms are in the tube. Different atoms glow at different wavelengths, or colors. Cool, huh?

The fluorescent bulbs that you have in your house contain mostly Mercury, but will also contain some other gases as well. Including more types of gases increases the number of colors represented in the light that comes from your light bulb since different types of molecules emit different colors. This helps the light appear more like white light. Unfortunately, it also decreases the efficiency of the light bulbs.

Incandescent light bulbs have all the colors of the rainbow and therefore look more like white light. This is easier on our eyes since our eyes developed to be accustomed to sunlight. However, they are terribly inefficient. Fluorescent bulbs, or compact fluorescents as we call the smaller bulbs used in our homes, are less like sunlight and therefore harder on our eyes, but require much less energy to produce the same amount of brightness as the incandescents.

Below are pictures of the two types of light bulbs along with their spectra. A compact fluorescent is shown at top left with its spectra at top right. An incandescent bulb is at bottom left with its spectra at bottom right.

Next week we will look at another increasingly common light source in homes: Light Emitting Diodes, or LEDs. Once we have a good understanding of all the lights in the house, we can hopefully solve the mystery of my daughter’s nightlight.

Side Note: For those of you who like to play with simulations, the PhET website has a great one on the models of the atoms. Click here, then run the simulation, select Experiment from the top left and choose Bohr from the types of models. It will show you what happens when you shine light on an atom to give it energy and then watch as it emits photons. If you click Show Spectrometer on the bottom right, you will see what colors Hydrogen emits.