Introduction – What is Light?

We non-scientists take for granted that light is just light, and hardly think about where it comes from or how it’s produced.  So if your work involves light, lighting or even indoor farming, we thought you might like to know.

This article pulls back the curtains on “What is Light?”.

Light is a release of energy.

In short,  photons of light that are being emitted from a light source (e.g. incandescent bulb) is simply a release of energy.  To explain this lets take an analogy of a snapping rubber band.

Let’s say you apply physical energy to pull the rubber band apart.  This imparts the energy into the rubber band material as potential energy.  When you release one end, the rubber band contracts quickly and you hear a SNAP!  The snap is the potential energy released in the form of sound.

Let’s start with the electron in it’s natural low orbit (Fig 4-a).

When you apply energy or electricity to the bulb,  the electron in the atom of the filament will be excited to a higher orbit and will have obtained potential energy (Fig 4-b).

When the electron snaps back to its lower state or natural state (Fig 4-c), it will release the energy – But instead of a sound, it releases a photon of light.

Ergo, light is simply a release of energy – And though other types of lights (LEDs, fluorescent, etc.) differ in many ways, they still have the same end result of emitting photons of light by allowing electrons to fall from higher orbitals or states to lower ones.

Electrons don’t stay in a higher orbit, even with constant electricity.

Why don’t electrons continue to stay in a higher orbit – after all, constant electricity is being continuously applied.

Electrons in high orbit are like someone on a high wire (tightrope).  They are always in a very precarious, unstable state, and it’s easy for them to fall out of high orbit.  But why are electrons unstable at this state?

Physics and Quantum Mechanics

In short, subatomic particles like electrons are weird. They live in the world of the very small, the world of Quantum Mechanics.  This means that things don’t behave the same as our own worldly existence of touch, hear, see, and smell.

The very existence of an electron at any one location in time is uncertain, making its position on the high wire precarious.  So, they easily fall and emit a photon of light.

And because of the constant electricity that is applied, the next electron is elevated to the higher state, and it soon falls off – and it is this continuous rise and fall of billions of electrons that gives us this stream of light from a light bulb.

Classical and Quantum view of electrons (deep dive).

Some will argue that my classical description of the atom, nucleus and orbiting electrons is inaccurate. I will concur, but this is how it’s still being taught in classrooms to help students “ease” into the complexities of physics and chemistry.

In the Quantum world, the electron exists as an electron cloud. This infers that the electron is forever popping in and out of existence around the nucleus but is never in one place unless observed.

Don’t worry if you don’t get it – even our brightest scientists have yet to unravel  Quantum Mechanics completely. But that’s why electrons remain weird, and that’s why their position in time and space will always be precarious.

Light is both particle and wave 

It’s easy to perceive light as particles because of its behavior: It bounces off walls and mirrors, much like a tennis ball would. Though we can’t see the particles of light, we deduce they are because of their behavior.

Light, at the same time, is also a wave, not that we can see light as watery-like waves, but because of the behavior.   There was a famous experiment called the double-slit experiment where light was sent through two slits and the outcome was surprisingly similar to how water waves goes through those same two slits.  Because light behaved as both particle and wave, it was deemed light was both.

Using a spectrometer to distinguish particle and wave

A light meter can measure and see both particle and wave aspects of light. Light is made of particles called photons. A  spectrometer or light meter can measure the number of photons coming from light by measuring LUX or PPFD (grow lights).  The higher the LUX, the more photons are hitting a square meter.

A spectrometer is a sophisticated light meter that can also measure waves, and these waves have a frequency associated with a specific color.  Bluer colors have a shorter frequencies and Red colors have longer frequencies.

Each photon has an associated wavelength frequency, which determines its color, and a spectrum taken by the spectrometer can show the relative number of photons for every visible color in a light.

Fig 11 Bluer colors have shorter frequencies, Red has longer

Conclusion – Pulling back the curtains on What is Light.

Light is a release of energy, just like a snapping rubber band.  You have to understand orbiting electrons that get pushed to a higher state.  Because of the uncertainties of their existence, electrons easily fall back to their natural state, releasing energy as photons.  This continuous rise and fall of billions of electrons produces a stream of light that we don’t need to take for granted anymore.

Anyone can be a scientist!