LUMOS! HOW COULD A WAND GIVE OFF LIGHT?

In the wizarding world, there is a handy piece of magic that can turn a witch or wizard’s wand into a torch without a flame. Before the invention of electric lights, owning an instrument that could be commanded to give off light at will would have been a remarkable thing indeed.

Although nowadays such an illuminating device wouldn’t seem that remarkable, excepting the fact that its light is produced from the end of what is essentially a pointy stick. Many people carry around their cellphones, which have multiple functions, including instant light. There is even a function on Android phones where the user can just say Lumos on the Google app, to activate their phone’s torch. They can also say Nox to turn it back off.

In this way, muggles daily brandish their cellphones as a light source in a similar way to wizard’s wielding their wands. So, what would be needed to get a wand to give off light like a torch?

Lumos!

This literally enlightening charm is one of the best ways a wizard has of shedding light on dismally lit situations. Once engaged, a wizard’s wand will emit light from the tip as if it were fashioned from E.T.’s finger.

When a life form uses internal reactions to create light the process is called bioluminescence. Fireflies, glow worms, angler fish, and various other animals have this ability to produce light at will but the light is often blue, green, or sometimes even red. As a wand is not a life form, we can disregard bioluminescence as the light producing mechanism.

Light can also be emitted by mixing two chemicals together. The chemicals react and give off light through a process called chemiluminescence. This is how glow sticks work. They come in a variety of colors and can be made to shine very brightly if heated, although the size of the glowing wand tip would limit the amount of light that can actually be given off. The light emission can also be stopped by making them extremely cold. So chemiluminescence is a possible candidate.

Generally, when it comes to light emission there are many possible sources but the most common involve either incandescence or luminescence. Incandescence involves light given off as a result of the temperature of matter, whereas luminescence is light given off regardless of the matter’s temperature. In regard to wands this means that if Lumos works via incandescence then the wand should also be giving off a detectable amount of heat, whereas if it functions through luminescence then the wand could work as a much cooler light source.

Making light

Light is a form of electromagnetic (EM) radiation, transmitted as photons carrying different energies. Generally, the photons that bring us light are a result of the absorption and emission of energy by the electrons in atoms. Electrons only absorb and release energy in particular amounts, known as quanta.

Regarding luminescence, this absorbed energy can come from a variety of sources, with each type of luminescence identified by its particular energy source. For example, electroluminescence is caused by electricity, sonoluminescence is triggered by sound and photoluminescence is instigated by energy from photons.

When an electron absorbs this energy, it rises to a higher energy level, and the atom is said to be in an excited state. Straight afterward, the electron reemits that energy as a photon, causing the electron to drop back down to its original energy level; returning the atom to an unexcited or ground state. The photons emitted from the atom have different frequencies corresponding to the amount of energy they carry. The higher the photon’s frequency, the more energy it has.

The frequencies of electromagnetic radiation that we can perceive with our eyes is known as visible light, encompassing the entire spectrum of colors that we can see in rainbows. Each hue or color of a rainbow corresponds to a particular frequency of visible light. Red light is the lowest frequency we can see, at roughly 430 terahertz, and the highest frequency we can see is about 770 terahertz; the frequency of blue light.

When we see light it’s normally composed of a range of different frequencies, i.e., it’s a conglomeration of different hues. If there is a bigger intensity in any particular frequency, then overall the light appears to gain slightly more of that hue. However, if all the frequencies of visible light are present in roughly similar proportions then overall, we perceive it as white light.

The fact that the Lumos charm gives off a brilliant white light indicates that the wand is giving off photons from all parts of the visible spectrum. These photons can be produced by using any of the many different forms of luminescence. Each one has its own benefits for producing light with a wand, although luminescence isn’t the only available option.

Incandescence

All objects that are not at absolute zero (the coldest temperature possible, -273°C), emit photons in the form of thermal radiation. This process is known as incandescence.

If the object giving off the light is opaque, (so that most of the light coming from it is from itself, rather than reflected) then the object can be regarded as what’s called a black body. In line with that, the electromagnetic (EM) radiation it gives off is considered as black body radiation.

At about 525°C, called the Draper point, most solid materials will start to visibly glow. At that temperature, the peak frequency of EM radiation is in the infrared but as some of the emission reaches into the red end of the visible spectrum, we are able to register the radiation as a dull red glow.

This is why when an incandescent light bulb is dimmed to low light (and temperature), the filament can be seen glowing red. Increasing its temperature increases the intensity of light given off (it gets brighter) as well as the peak frequency of the light. This makes its color change from red through to orange, yellow, and then white at the hottest temperatures, hence the term “white hot” for describing extreme heat.

At the temperatures that it’s exposed to, the lightbulb’s Tungsten filament would quickly burn out if there was oxygen present. This is why filaments are contained within a bulb that does not contain oxygen. This used to be achieved by creating a vacuum inside of the bulb, but later it was found that filling it with an inert gas like argon can slow down the evaporation of the filament, allowing it to operate at higher temperatures.

The tip of a wand could be heated until it emitted visible light, but being in an environment with oxygen means it would catch alight and burn away. This would be exacerbated by the fact that the wand is made of wood, which is far less robust than the more resilient tungsten which is used as the filament in the majority of incandescent bulbs. However, each wand does also have a core of some magical substance such as unicorn tail hair, dragon heartstring or phoenix feather. Maybe these magical substances act like filaments with properties far greater than tungsten.

Lumos Solem: Recreating Sunlight

In the movie, Harry Potter and the Sorcerer’s Stone, Hermione uses the lumos solem charm to produce a strong beam of light to mimic sunlight. Could sunlight be replicated in a wand?

At their core, stars rely on thermonuclear fusion to provide the energy for photon production. Under immense pressure and temperature, atomic nuclei are fused together in the core of stars. This releases energy which gradually reaches the surface layer of the star, called the photosphere. The atoms in the photosphere absorb the energy, then release it again as mostly visible light. The actual source of visible light in a star is the photosphere, which is releasing photons as a result of its electrons being energized by radiation from within the star.

The layers beneath the photosphere are also too dense to be penetrated by visible light, meaning the star is essentially opaque beneath the photosphere. As such, a star can be considered almost like a black body and acts as an incandescent light source. In this way, although a bulb can’t provide an exact light match to the sun, it still shares the property of being an incandescent light source. Could we simply put a small light bulb into the tip of a wand to provide a Lumos function?

Well, small incandescent light bulbs were first incorporated into torches or flashlights around 1900. They were powered by electricity from dry-cell batteries. These bulbs had limits on how long they’d last and how bright they could shine. Nowadays, incandescent bulbs can be made as small as a quarter of an inch in length, with powers of 0.3 Watts. If one could be placed on the end of a wand and supplied with an adequate power source, then a Lumos like white light could be emitted. Providing such a bulb could be supplied with enough electrical energy and made robust enough to be operated at high temperatures, it could provide a crude light on the tip of a wand.

A more effective option would be to use Light Emitting Diodes (LEDs) to provide torch light. Unlike incandescent bulbs, they function through electroluminescence. In their operation, the LEDs also don’t give off as much waste heat energy as incandescent light sources, so LEDs are more efficient. As a result, they require smaller power supplies to produce the same strength light and they can be made much smaller.

Lumos Maxima

In The Prisoner of Azkaban, Harry Potter uses Lumos Maxima, to emit the greatest form of wand light that can be produced. It essentially turns a wand into a flood light.

The brighter the light is, the more photons are being released every second. To release more photons, we would have to increase the surface area that is emitting the photons. This would be like causing the wand to give off light from half of its length instead of just the tip. More surface area means more photons given off, meaning the light is brighter.

With incandescent light sources, we could increase the number of photons being released by raising the temperature, although this would slightly change the frequency of the peak radiation and so the color would change as well. So, ruling out the possibility of the wand being a white hot incandescent light source, we’re left with a cooler luminescent light source, such as the LED torch on a cellphone or white LED screen.

If the light from the wand is a result of luminescence, then depending on the exact method, it would require an increase in the rate of light producing reactions. This could be done by increasing the temperature of the reactions, or the voltage supplied, or whatever other process underlies the light production.

So, a wand with a brightly glowing tip could be made in a few ways. However, whatever the exact process of creating the light, it would still depend on electrons being excited to higher energy levels then emitting that energy again as light.