Light Bulbs are Literally a Waste (and that’s the point!)

 

We often take for granted the ubiquity of electric lighting is these days.  Just a few hundreds years ago we didn’t even know the basic principles behind electricity.  All we could do is cower at lightning every once in a while, and if the stories are true then maybe you’d tie a key to a kite in a lightning storm to see what happens.  And yet in other parts of the world (if you’re from the US/Canada), lights are a hot commodity.  We know they run off of electricity, but one may be hard-pressed to really explain just how the things work.  It’s actually much, much simpler than you thought (probably).

There’s a fundamental concept of energy transformation in science that says any time you convert between types of energy, you lose some of it in the process.  It’s like saying you can go to the casino and blow a thousand bucks on slots, and you might break even at the end of the day, but the time you spent pulling the lever is now lost.  In terms of energy, we might say that if you drop a rock off a cliff, the energy it has when it gets near the bottom is mainly in the form of speed – you wouldn’t want to be standing under it, would you?  It’s chock full of energy that was transformed from potential to kinetic (in this case, from its high position to its high speed during the fall).

In the same way, light bulbs and all concepts of electricity essentially incorporate this energy loss into their design.  Commonly the energy that’s lost during a transformation is either heat or light, or both.  Hm… can you think of any devices that put out heat and light?  Hopefully there’s a light bulb over your head right now, because that’s exactly what we’re referring to here.  The bulb on the left here is getting so hot that it’s producing light.  Ever wonder why a stove’s coils burn red hot?  That’s light being emitted along with heat.

The bulb itself is little more than a single piece of wire that’s conducting.  We know intuitively that rubber doesn’t conduct electricity that well, but most metals do, so we use metallic wire here.  You run your single wire from an initial power source and through the bulb, making sure that only a single path exists and that the wire never touches itself farther down.  The wire comes out of the bulb and connects back to the power source, making a circle, or a circuit.  If you’ve got a D battery at one end, you can hook your piece of wire to the two ends of the battery, run the body of the wire through a bulb, and produce some light from it!

The trick here is that inside the light bulb there is a section of tightly coiling wire.  You can see it clearly in the picture above.  As electricity flows through this section, it encounters resistance, just like you might if you were running down a straight hallway and suddenly had to turn multiple corners as fast as you possibly could.  The electricity is forced to slow down here, and because all energy is conserved, the energy that was previously shooting down the wire is split off into an equal magnitude but different form of energy, namely, heat.  As a result, the wire gets really, really hot.  Rub your hands quickly together and the resistance between them causes heat to be generated, which we love to do in the winter when it’s freezing cold outside.  It’s the exact same principle – friction between two objects “generates” heat energy.  Also important here is that we can change the resistance to virtually any value we please, making it easier or more difficult for electricity to pass through or generate some heat.

As the wire gets hotter and hotter, it eventually starts to put out light.  This light energy is another manifestation of the wasted energy from this transformation process.  But this is exactly the reason we use light bulbs in the first place!  What we’ve essentially done is force energy into a conducting wire, force it into a bulb, and finally force it to splinter off into several kinds of energy that are observable in different ways.  We can feel the heat from a light bulb, we can see the light it emits, and we can test the wire to see whether there’s still energy flowing through it.

In essence, the resistance we give the light bulb at the coiled section expends the energy we’ve fed it, so the result is a great deal of heat and a great deal of light.  The interesting part is that a light bulb is basically just the guts to any electric appliance, like a microwave or a refrigerator.  If you had your wire connecting to a microwave instead of a light bulb, you’d get some power into it and you could make hot chocolate.  Light bulbs by design don’t have any useful function except to release electrical energy – they can’t power a hair dryer by themselves.  All the energy you’d spend charging your phone at night is instead released by a light bulb to provide a continuous stream of light.  Here’s the kicker though: you might guess that only a small fraction of the total energy goes towards light and heat release.  Unfortunately, if we take 100 units of some arbitrary energy and send it through a light bulb, only 3 of those units are really producing the light we need –all the other 97 units are wasted as heat, which is why leaving lights on in the summer makes a room really hot (or why a spotlight on a school’s auditorium stage makes you sweat!)

This huge waste of energy as heat that we don’t need is an ongoing problem as we try to develop better light bulbs.  A big hurdle is that the light we need from light bulbs is really a result of the release of heat, so it’s hard to have one without the other.

When you think about it, the very purpose of a light bulb is to be wasteful.  We want that electrical energy to be released, rather than contained in the conducting wire, because its release provides us with a huge amount of heat and a relatively small amount light.  A light bulb’s energy  disperses as heat and light much like any electrical device might, but in a much greater quantity than any hair dryer or electric razor.  Most of the energy we put into those devices actually goes towards useful work (the hair dryer spitting out hot air, or the razor’s blades whirring).  On the other hand, the light bulb is like an appliance without a function – energy runs through it, is entirely wasted, and just happens to produce some light as a by-product.

As for the eventual heat death of the universe due to the effects of entropy, well, that’s a discussion for another time.

It’s a Math, Math, Math, Math World

Consider a mental inventory of your own knowledge for a moment.  Picture a big pile of all the things you know: concepts, processes, ideas about the world and humanity, equations, whatever.  It’s hard to quantify but I bet you’ve got a decently-sized pile.  Now next to that stack up a pile of the things you don’t know: all the subjects you wished you’d had time for in college, the equations that we’ve yet to derive, the contents of the universe, and so on.  You’ll find that the pile of unknowns is to the pile of knowns as planet earth is to an electron in a single atom of helium.  That is to say, the amount of stuff you or I or even collective civilization knows about the world is a lot, but it pales in comparison to what we wished we knew.

All of this to say that there are plenty of things we’re confident about.  We live in a world where the newest sub-atomic particles are being tested and analyzed, but we still can’t quite figure out how our brains really work.  We can send men to other planets, and yet we’re sorely lacking if asked for a good reason why humans need sleep at all.  Our world is huge and unfathomably complex, and yet we have somehow (and I’ll never believe this) have been able to distill at least parts our world down to math and equations.

If you throw a ball up in the air, could you give someone a qualitative description of its action?  “It left my hand and shot upwards, then slowed down to a point and came back down to earth pretty quickly.”  Well, this isn’t exactly a scientific description, so how about something quantitative?  Not only can we determine speeds, accelerations, and distances traveled by nearly any object in motion, but we’ve learned that the variables that go into the motion of such an object are really few in number.  Armed with only a starting velocity, acceleration, and stopwatch, we can accurately determine the motion of objects.  In essence, consider everything that has ever left the crust of the earth and has been temporarily under the control of only the gravitational force.  We can describe its motion near-perfectly.  Indeed, we can use the equations to the right, each of which are essentially the same statement but re-arranged four different ways.

In my mind, the fact that we can need only 3 or 4 variables to describe motion on earth is astounding — there are few, if any, hidden variables that we don’t yet know about in many of our “knowns.”  Compared to the stuff we don’t know, we have somehow culled all the things we do know about motion in the right combination such that “motion of objects” is contained in our “knowns” pile.  The odds of this happening in any universe are, in my mind, astronomically low, but of course I’ve got no evidence to back up that claim.

We can measure invisible electric and magnetic fields with pinpoint mathematical accuracy and tell our friends the time to the nearest millionth of any given day (excluding leap seconds here).  This is stuff we know and have tested over and over – somehow these properties of earth and the universe ended up in our teensy weensy “knowns” pile.

One more example: Say you pump some oxygen gas into a room with no ventilation.  If you know the temperature and pressure of the room, you can use a very simple math equation (PV = NRT) to find out the volume of that room (and consequently the oxygen gas you pumped into it).  Let’s look at that equation a little closer.

The pressure exerted by a bucket of oxygen molecules: PV = NRT (where P is a pressure, V is a volume, N and R are constants, and T is the temperature)

Scientists agree that the product of pressure and volume is numerically equal to the temperature and two constants in any given situation.  Of course there are some correcting factors for advanced chemist fanatics, but even they’re not too terribly complex.  In short, this equation with only 3 variables and 2 constants fully describes the behavior of nearly any gas in any size room and at any temperature.

Have we really distilled molecular behavior into such a simple formula?  It’s kind of hard to believe, but this is once again in our “knowns” pile.  The whole point of this post is to spark a thought in your mind: with all the stuff that we don’t know, we still have lots that we DO know, and the stuff that we do know can sometimes be the simplest principles.  We can combine the very firm theory behind the laws of motion and flight to get airplanes running; we can measure the density and buoyancy of any liquid matter inside a column and then find the pressure it exerts at any depth inside the column.

Someday we’ll be able to map out the motion of atoms during nuclear fusion, or realize that the perfectly efficient engine is just a combination of the right four or five variables.  There’s so much to learn and so much to know that we haven’t even begun to study, and once we’ve got it all under our belts there’s a good chance that some currently unexplained phenomenon will be accurately represented with an equation — nothing more than a few letters and an equals sign.