My 4 year old asked about the sun and light bulbs. Describing the mechanisms (hydrogen or electricity) and why they, as opposed to other chemicals, make brightness totally threw me for a loop.
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All objects emit electromagnetic radiation according to their temperature. The higher the temperature, the shorter the wavelength of that radiation. Warm human bodies emit infrared radiation, which is longer waves than visible light. A hot iron emits red visible light. The lightbulb wire and the Sun emit yellow-white light.
There are different kinds of lights.
1) Heat. All objects give off light based on their temperature. Normally, this light is a kind our eyes can’t see, but very hot objects, the the filament in a light bulb, or a fire, or a hot piece of metal, are hot enough to give off light our eyes *can* see. That’s how old lightbulbs work. Run a ton of electricity through a thin piece of metal, it gets super hot, and we see light.
2) “Energy” and electrons – if you take certain gases, put them in a glass tube, and put a metal plate on either end and supply it with electricity on one end, the electricity will “jump” through the gas which gives the gas “energy” (different from heat). The gas doesn’t want to keep this energy so it sheds it in the form of light but we typically still can’t see it. So if you coat the inside of the glass tube with a special glow-in-the-dark-paint, the paint will absorb we can’t see, gain that energy, and then give that energy back off in light we CAN see. This is the same as those glow-in-the-dark stickers kids sometimes get. The paint is sort of like a light-battery, it absorbs it and gives it back off later. That’s a “fluorescent” bulb.
3) Crazy physics and electrons – there is a special computer chip-thing called a “diode”. Diodes can do some neat things, but in a special application if you run electricity through them they can release light. These are really hard to explain like you’re 5.
So the 1st option, heat, simply uses electricity to generate heat in a wire, it’s not very efficient because heat is, well, *hot*. That implies most of the energy is being wasted in making a hot light bulb instead of making light. The middle option, fluorescents, are better in that they use electricity more efficiently (less waste heat) but they do produce some AND they use some nasty chemicals, so better but not great. Finally LEDs produce almost no heat and are cleaner to produce, PLUS they last *a lot* longer than the others. So they’re “the best”.
Fun Fact – A lot of office buildings factored in the waste heat of lighting into their calculations for designing heating and cooling systems. A lot of older buildings are “cold” because the have had high efficiency lighting installed aren’t producing enough heat to function properly.
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Ultimately it’s atoms, they have electrons that orbit and they have a nucleus with protons and neutrons. Every material is ultimately made of atoms.
So any form of energy that goes into an object, whether you’re heating up a spoon in a flame until it glows red, or electricity heats up the thin metal wire in a light bulb, etc., all that energy goes into the atoms that make up the material.
So the atoms want to get rid of that energy, and the one way they have is to emit light. Light is composed of little bits of energy that we call photons; the atom’s electrons or nucleus just create them to shed accumulated energy.
Spoon stops glowing when you take it out of the fire, light bulb turns off if you cut the electricity flow to it, etc. The Sun is very big and will have enough pressure and material to shine for another 4 billion years; we’re basically half way through the Sun’s “reserves” of energy, but it will also stop shining at the end of its life.
So basically, energy goes into the atoms, and the way they get rid of energy is to create little bits of energy we call photons of light.
Light is energy; we see it as light because our eyes and brain interpret it as light and colors. Sound is just the vibration of air, we hear it as sound, words, music, etc., because or brains interpret it as such.
For the purposes of explaining things to your Son, it’s a good idea to frame things in terms of Energy. Then point to how various machines transform energy from one kind into another.
A Torch converts electrical energy into Light. A CD player into Sound. An oven into heat.
This is highly simplified of course. But its a good basis to build upon to then say that the sun in a source of Energy.
As for how light is actually made… That’s a little tricker to explain to someone that has no concept of subatomic particles.
You may have heard of a Photon. A Photon is a tiny tiny piece of energy. It comes in lots of different forms. Or appears to. Heat, Light, X-Rays, Radio Waves. But it’s all really the same stuff. Realising this was an important step in the building blocks of modern physics.
Whenever something is happening that creates light, it means something is producing lots of photons.
There are better descriptions of precisely what that means. But the best way to describe it to your Son is that light is one of a the ways in which energy moves from one place to another.
Charges create electrical fields (they attract or repel other charges) and moving charges create magnetic fields (which exert forces on other moving charges). If charges are moving around in a way that is changing in time, they create electromagnetic waves, moving electrical and magnetic fields which propagate outward from their source. Visible light is a subset of electromagnetic radiation.
In the case of chemical energy or heat energy being converted into light, the (charged) electrons in the relevant material are excited, and they can give off energy in the form of light. To fully understand this process you need quantum electrodynamics, but I think it’s sufficient to say that high energy electrons can become low energy electrons, and give off light in the process.
All charged particles can emit photons by changing the amount of energy they have.
In something hot, electrons and atomic nuclei are constantly bouncing around, going faster and slower, briefly bonding with things and then loosening or breaking those bonds. Every time this happens there is some chance of emitting a photon. If it’s a very strong bond that formed (atoms or molecules violently snapping into place, or an electron falling very close to a nucleus), the photon emitted will have a lot of energy, so it will be in the visible/ultraviolent spectrum. If it was weak, the photon will have less energy, so it would be on the infrared side of the spectrum. Likewise, if a charged particle slows down a lot, it will emit a high energy photon, and if it slows down a little bit it’ll emit a lower energy photons.
In old light bulbs, the mechanism was the same. The filament would get hot, and all of this bouncing around of electrons throughout the metal, and of the metal atoms against each other, would emit photons. In newer LED bulbs, we have more direct ways of harnessing the electricity, by moving electrons through a substance where we can control how much energy electrons lose and gain. That way we can make sure all of the light is visible light, and we don’t accidentally emit infrared or ultraviolet light that isn’t useful to us.
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