How do fluorescent lights work? They pass an electric current through a low-pressure mercury-vapor, which produces light. A fluorescent light is made of a tube of glass that has a tungsten electrode at each end. Inside the tube is a tiny amount of mercury and an inert gas. There is a phosphor powder coated along the inside of the glass tube.
The inert gas that is used is Argon. An inert gas is a gas that does not form chemical reactions with other elements. They are also often called noble gasses, which is a translation from the German Edelgas. Many gasses are very reactive, such as Oxygen. When oxygen comes into contact with iron, the oxygen reacts with the iron and forms iron oxide: rust. There are six natural inert gases and one synthetic one. The natural ones are Helium, Neon, Argon, Krypton, Xenon, and Radon. The synthetic one is Organesson. Because inert gasses don’t react, they are nontoxic and noncombustible, which is why they are used in fluorescent lights.
When you switch on a fluorescent light, electricity enters the tube at one end and crosses to the electrode on the other end. As it crosses, it gives energy to the liquid mercury and the mercury becomes a gas, expanding in volume. The electricity continues to cross the tube, but every time an electron or a charged atom hits a mercury atom, they impart energy to the mercury atom. The electrons around the mercury atom jump to a higher orbit, but they don’t like to stay there, so they quickly release the extra energy as a photon. There is a lot of energy and the photon has a high wavelength, so it is ultraviolet light. Unfortunately, unlike some animals, we cannot see ultraviolet light, so it is no use to us. Luckily, a property of phosphor is that it can turn ultraviolet light into visible light. This is why the glass tube is coated in phosphor powder. Phosphors give off light when they are exposed to light. The phosphor atom takes in the energy from the ultraviolet light, its electrons jump to a higher orbit, but when they release their energy they release slightly less than before, and the wavelength of the light is in the visible range for us. That is how we get light from a fluorescent light.
Before the light is switched on, there is no current flowing through the tube. When the power is applied, the tungsten electrodes heat up rapidly. When they are hot enough, they start to boil off electrons that flow into the tube. The Argon gas in the tube isn’t very conductive to start with, but the electrons from the tungsten electrode start to attach themselves to the Argon molecules, ionizing them and increasing the conductivity of the gas. When the conductivity is high enough, the current can carry all the way to the other electrode and the light will come on.
So, what is the Argon for? It performs four functions. Firstly, it protects the electrodes at each end of the glass tube. The oxygen present in the light will oxidize and corrode the elements at each end of the light. The Argon keeps the oxygen molecules away and gives the light a longer light. The second reason is to serve as the current carrier to begin the lighting up process. The third reason is to keep the balance of the amount of mercury atoms that are being turned into a gas so as to increase the lamp’s efficiency. And the fourth reason is to make sure the light photons are emitted in a random pattern. Without the gas, all of the light would go in the same direction.
One problem with the Argon is that its resistance decreases as more atoms are ionized. This means the current crossing the lamp can continue to increase until the lamp could potentially explode. To prevent this, fluorescent lights have something called a ballast, which controls the amount of current going into the light. Because the AC current switches back and forth very quickly, the ballast is constantly increasing and decreasing the current, which is why fluorescent lights hum.
Fluorescent lights are about 6 times more efficient than a regular incandescent light bulb, but they are still nowhere near as efficient as an LED light. They also contain small amounts of mercury, which needs to be taken into consideration when they are disposed of.
Fluorescent lights can be used for other purposes as well. If the phosphor coating on the light is changed to a slightly different kind, they can emit long wave ultraviolet light, which makes the good as black lights. With another small change, they can be used in tanning beds.
So, a fluorescent lamp works by vaporizing mercury with an electric charge to make it give off ultraviolet radiation and then changing this ultraviolet light to visible light by using phosphor powder. And this is what I learned today.
Sources
https://www.safeopedia.com/definition/9067/inert-gas
https://en.wikipedia.org/wiki/Noble_gas
https://en.wikipedia.org/wiki/Fluorescent_lamp
https://home.howstuffworks.com/fluorescent-lamp2.htm
https://lessismore.org/materials/102-fluorescent-light-tubes/
http://www.lamptech.co.uk/Documents/FL%20Gases.htm
https://edisontechcenter.org/Fluorescent.html