What Color is Lightning in a Beaker?

Kids pointing in snorkeling gear in pool.

Thunderstorms can be incredible to experience. From the bright flash of lightning that is often almost to fast too see, to the immense crack of nearby thunder that can make your heart feel like it skips a beat, they truly are a demonstration of the power of nature.
Image Credit: NASA
They are also full of interesting science! For instance, lightning usually carries between 100 million and 1 billion volts of electricity! This allows it to jump all the way from clouds to the ground, and as it does so, some of that energy is transferred to the atoms in the air. This energy is released as light, which is how we see it. 
This means that it is the air itself which determines what the air looks like. On Earth, our air is made up of about 78% nitrogen, 21% oxygen, and a bunch of other gases like water vapor, carbon dioxide and argon. When we put electricity through it, it gives off a characteristic glow:
The Oudin Coil generates up to 50,000 volts of electricity–much much less than a thunderstorm. This allows the electricity to jump about an inch, rather than the miles between clouds or to the ground of an actual lightning strike. However, when it arcs through the air, this still produces a similar look and identical color1.
Lets see what it would look like in a different environment. The beaker in this gif has a bunch of dry ice–which is just solid carbon dioxide–at the bottom. Unlike regular ice, dry ice doesn’t turn into a liquid, but instead skips straight to carbon dioxide gas! This gas is more dense than air, so the beaker ends up full of just carbon dioxide, which is a much different composition than our atmosphere. Check out what happens to the lightning in there!
Unfortunately, we can’t try this particular method with every gas for several reasons. First of all, not all gases are heavier than air. This would make it hard to keep it in the beaker. In addition, other gases might explode, or worse, if exposed to electricity with oxygen around in this way. Still other gases can be very toxic. Fortunately, we have some tubes of gas and a machine that puts electricity through it in a similar way. In this gif, the gas tubes are viewed through a diffraction grating which breaks up the light into the different colors of the rainbow contained within. This is actually a whole different branch of science which is used to figure out what elements different things are made of just by seeing the light that comes from them! Learn more about that here.
Written By: Scott Alton
1People actually report lightning to be many different colors. In general, nearby lightning will have a purple glow due to the composition of the atmosphere, and the central part will look white simply because it is so overpoweringly bright and doesn’t give time for eyes to adjust. Most other colors that are reported are because the lightning is being viewed from a long ways off and the light has to travel through dust, rain, haze, pollution, or other things that can change its color.