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:
- 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.
- 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!