Rad Scientist- Fluorescent Light


Urban Dictionary tells me that rad is, “a term made popular by the Teenage Mutant Ninja Turtles, still primarily used by people on the West Coast”. Since I am neither a Teenage Mutant Ninja Turtle nor from the West Coast, this installation of the Rad Scientist will focus on the gnarly fluorescent lights gracing the ceilings of Baltimore School for the Arts. As a side note, Urban Dictionary defines gnarly as “when you’ve gone beyond radical, beyond extreme” so I urge the florescent lights to take no offense in my change of adjective.

You light bulb enthusiasts out there might already know this, but for the rest of you, I should note that there are many different kinds of fluorescent lights. I will discuss mainly hot cathode lights, which are pretty gnarly (in my opinion). In a hot cathode light, tungsten filaments are at either end of a glass tube coated with phosphors. The glass tube also has small drops of mercury at either end, close to the filaments. Inside of the tube is an inert gas, usually argon. When the light is heated up, electrons form a current through the gas (with the help of ions and free electrons) and excite it into producing U.V. light, which is made visible by the phosphors. Fluorescent lights, like most things you use, are powered by AC (alternating current), which runs through the circuit back and forth, switching directions constantly. Once the AC can move through the gas and back, you have your self a working fluorescent lamp.

Once the lamp is running it’s smooth sailing, but the real gnarly part happens before the bulb starts to shine. Fun fact: It is really hard to get a current to run through a gas, especially if that gas is cold. Hot cathode lights get their name because the gas inside of them has to heat up before the light can shine properly. When the fluorescent light first gets turned on, it has to find a way to force electrons through the gas inside of the tube. To do this, the current is sent first through a larger circuit that also includes wires attached to a little metal switch. As the alternating current runs through the circuit, it heats up the filaments in the tube and the switch. At this point, the filaments are starting to heat up and ionize the gas around them. The ionized gas, a.k.a. plasma, makes the ends of the tube glow, but the current is still not able to travel through the lamp. Here’s where that little metal switch comes into play. Once the switch is hot enough, it pops into the circuit, causing what is called an inductive kick. The inductive kick comes from the collapse of a magnetic field around a transformer. This transformer is located in a mechanism called a ballast, a part of the lamp. The transformer, or “choke”, creates a magnetic field as the alternating current flows through it, and when the field collapses, it sends a jolt of high voltage (electric current) through the system. The inductive kick forces the current through the gas in the tube and the light turns on.

Now that the lamp is working, and the current is flowing through it, more and more of the gas molecules become ionized. If left unchecked, this process would cause the lamp to short out, or simply melt. Good thing for us, fluorescent lights are outfitted with either a magnetic or electronic ballast which not only provide an inductive kick, but also prevent the lamp from breaking down. Magnetic ballasts are bigger and bulkier than the electronic ballasts, but can last longer. There you have it, if you’ve made it this far, you know pretty much how fluorescent lights work. Cold cathode fluorescent lights (or CCFLs) work pretty much in the same way as the hot cathode lights but with a more complicated ballast. I’d like to take a few sentences here and make a special shout out to www.edisontechcenter.org which has TONS of information on all kinds of light fixtures and awesome animations that explain how fluorescent lights work. If you’re interested in learning more, the website has a “Resources” section that explains how pretty much everything works. Do you know what a mercury arc rectifier is? Me neither, but it has its own page and explanation (which is pretty cool). Enjoy your exploration, and stay rad.