No Love for Tungsten

“Why is the Incandescent Light Bulb getting the BIG old boot in the modern era?”

Well it's really, really bad at doing what it was told to do, make light!

Imagine you hired a new employee to stock shelves at your local store but they only did their assigned job less than 10% of the time and more often than not it was more like less than 5%(I blame FaceBook). That's an incandescent light bulb. They are anywhere between 2-10% efficient depending on the type/quality. The remaining energy is released as heat, which is simply radiated off into the surrounding area.

“Why are they so inefficient?”

Well the design has not changed in over 100 yrs, dating back to Thomas Edison.  An incandescent light bulb is simply a piece of coiled metal, tungsten, which is placed into a glass tube under a vacuum (no oxygen gas present). Electricity is passed through the tungsten filament. As the electricity passes through the metal, this causes the filament to heat up and eventually glows white hot, roughly 2500° C/4600°F! In comparison, iron melts at around 1500° C/2700°F, now that’s warm to say the least. That’s why tungsten is used, or at least was. It has the highest melting point and tensile strength of all pure metals giving it longevity.

“So, why so bloody HOT?”

A tungsten filaments main job is to create resistance, to make it difficult for the electrons in the electrical current to flow through itself. As a result heat is generated as the electrons “flow” through the material. Now it’s not actually a flow, more like the most amazing examples of dominoes, but tungsten doesn’t make it easy. So heat is generated as particles try to move past one another. This is why it has to be in the glass bulb. 1) so you don’t touch the pretty glowing 2500° C/4600°F metal thingy, and 2) at those temperatures the tungsten will combust if any oxygen gas is present.

“So where does the light come from?”

As the heat builds and builds, the atoms inside the filament begin to vibrate more and more and more in their seats. It’s like feeding a toddler candy every 10 minutes on an 8 hour car trip if your goal was to get them to vibrate so fast they might burst right out of their seat belts! That’s like our goal in tungsten. It’s referred to as a Black Body Object. I know, sounds awesome, doesn’t it? (What’s even cooler is that Black Body objects exhibit what is known as the ultraviolet catastrophe, which could have destroyed the universe until we realized it won’t). Basically when an object gets SOOO hot, the particles are moving so fast back and forth, they will begin to emit radiation as heat, and eventually higher levels of radiation, light! And there lies the problem.

The amount of heat needed to get the particles to this sweet spot is extremely high, 2500° C/4600°F. It would be like feeding that toddler sugar again, as a means to get them to sing a song. After enough sugar they’ll be singing American Idol audition ballets. Not the easiest way to get the job done, but that’s essentially how we have been lighting our world for over 100 yrs. It’s like taking the long way to work, driving an extra 100 km when it’s only 5 km from your home. Not the most efficient means of getting there.

“So why are LED’s so much more efficient?”

Well let’s just say we have learnt better parenting techniques. More to come…

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