In the last post, I talked about using plasma as a source of lighting. Exciting electron flow in a low-pressure gas, electrons release energy in the form of light as the electrons drop from high energy orbitals to low energy orbitals.

However, there are also a lot of free-flowing electrons that have even more energy than electrons in high-energy orbitals. When they drop down to stable energy levels, the emitted energy overshoots the visible spectrum into the UV regime. Not only is this a drop in efficiency but it also poses health issues [for obvious reasons].

The nice thing about UV radiation is that it CAN be down-converted into visible light . The technical term for this process is Fluorescence. Electromagnetic energy gets absorbed by a specific material and gets re-emitted at a longer wavelength. Two quick technical factors:

1. To converse energy, the energy difference is absorbed by the material typically in the form of thermal energy (In – Out = Heat). So yes, the bulb does heat up over time, but not as fast as an incandescent bulb.
2. And since nature prefers disorder,  visible light will not be absorbed and emitted in the form of UV rays. The only extremely rare exception is when you have A LOT of EM energy in a confined space (anything weird like this is typically labeled “non-linear”).

Lots of things fluoresce! Natural things (like the rocks below) fluoresce a variety of colors when exposed to UV light.

Then again, humans also make a lot of artificial stuff that experiences the same effect (like your favorite energy drinks and alcoholic mixers)!

So where am I going with this….

A fluorescent light bulb is typically the same as a gas-discharge bulb [typically mercury-based], except they “spray” the inside of the glass tube with “phosphor” that ironically does not contain Phosphorus, the element. Instead of choosing gas mixtures, phosphors utilize a blend of elements to fine tune the final lighting color.

Even the phosphor thickness has its consequences. While the Mercury plasma emits primarily UV/Purple/Blue rays (high energy), the phosphor typically emits Green/Yellow/Red rays (low energy). A yellow/orange glow could be acquired by applying a thicker phosphor coating to the bulb permitting less purple/blue light radiation from escaping the bulb’s interior.

Note: Blacklights are basically the same thing except the bulb is coated in a material that filters out all radiation except everything between blue and near-UV (. And that is why “blacklights” glow purple!

In terms of efficiency, fluorescent light bulbs (~20%) are significantly more efficient than incandescent light bulbs (< 5%). And I hope you know why now!