What Causes Light Flickering?

Light flickering, believe it or not, is still without a definite explanation and “the subject of ongoing research” one source claims. It seems like something this common would have an explanation by now, but though there is not one grand unified accepted theory, lets explore the possibilities – and some may surprise you.

Context
(electrical engineers, skip this section)

First, some definitions: largely the subject of light flickering pertains to incandescent light bulbs as opposed to the more electronic fluorescent light bulbs, and unless otherwise specified in this article we will be referring to incandescent bulbs.

The operation of an incandescent bulb, for those new to the subject, is pretty rudimentary: take the alternating current (AC) line on one side, pass it through a tungsten filament, get heat and light, pass any leftover back to the neutral side. The end result is the ability to successfully find the toilet after the sun goes down at the flick of a switch. Applause.

The fluorescent bulb, however, involves a few more steps: the AC line is converted to direct current (DC), switched on and off at high frequencies by silicon transistors, passed through a tiny transformer located within the bulb to ramp up the voltage, then sent to either side of a (usually phosphorous) tube to make it glow. The end result, however, remains the same as long as the toilet has not moved.

But hold on, captain: that power going into the bulb in either case has some voodoo involved that is worth mentioning too! You see, in a perfect world where there is no war, no need for toilets to even exist and sunlight is perpetual, the line voltage put out by your outlets is a perfect wave at a constant (RMS) voltage, which is 120v here in the U.S.

And the wave alternates at 60 cycles per second (50 outside the U.S.), which is a key to some of the theories below.

But, alas, the world is not perfect as evidenced by…well pretty much everything right now including but not limited to my broke ass’s empty wallet. Therefore, the line voltage edges above and below the mandated utility levels due to weather, changing load demands around you (people unplugging and turning stuff on/off), and solar flares.

The frequency also fluctuates since it is proportional to the revolutions per minute that the generator spins at, which must change depending on the demand. Also, the waveform carries “harmonics” on it, or little waves atop the perfect wave that are the result of computers and other electronics pulling large amounts of current at inopportune times and thus distorting the wave for other devices down the line. Isn’t that kind?

So we’ve established the context – now onto the theory.

Natural Line Issues

So what causes incandescent bulbs to flicker? First off, it may just be the line: remember, the voltage cycles up and down at 60 cycles per second, and every time it reaches zero volts the bulb is effectively “off.” Our eyes can’t perceive that because of how fast it happens, but look at this picture:

The “dark spots” on the strings of light are where the voltage was zero while the camera shutter was snapping, invisible to the human eye but capturable by camera.

So say the line, during a “zero-crossing spot” in its natural cycle, suddenly experiences a power event such as a sudden massive draw in power as thousands of people suddenly turn on their televisions to tune in to American Idol, while a solar flare suddenly flares up and leeches power from the lines via environmental capacitance.

In this or a similar event that would make it harder for the power to recover from the zero volt crossing along its intended sine wave path, the light would effectively be “off” for a short duration of time visibly observed by the naked eye as a flicker.

Hehe, I just typed naked. Erm, right-continuing on…

The problem is theoretically less prevalent than in fluorescent bulbs, since the transformer (despite its size) would maintain a magnet field through the lapse in supplied power enough as a “buffer” to keep the phosphorus tube illuminated.

That’s the most probable theory, but there’s one more to explore using my somewhat shaky knowledge of electrochemistry and quantum physics – for all two people still reading this.

Quantum Effects

The tungsten used in incandescent bulbs is subject to electromagnetic interference at the quantum level.

Tungsten is a raw atomic element, and just like every other atomic element it is simply an atom comprised of a nucleus (protons + neutrons) with electrons circling around said nucleus. The electrons are displaced by the electrons in the alternating current passing through them, producing visible light and dissipating power as heat in the process.

However, the tungsten atom itself has a resonant frequency even as the AC current passes through it – a resonant frequency which can be matched by harmonics within the current from other power sources and disruptions on the line.

When this occurs, flickering is inevitable as a result: since the electrons are flowing across the atoms of tungsten, which each have their own electron spin states and electron holes, electron “grid lock” (in layman’s terms) may occur as the movements of all atoms cancel each other out, causing current to cease to product light across the filament visible as a flicker.

Or, external movements affecting the tungsten filament could cause slight imperfections within the filament caused at the time of manufacturing or created over time due to heat and operation cause the circuit to be broken for a brief moment and therefore a visible flicker.

Put simply, shaking the damn bulb any way can cause a flicker.

Relays

So far we’ve missed talking about a key piece of electricity: the utility side of things.

Your lamp is powered from a wall outlet. That wall outlet goes to your breaker box where it branches off your home’s power bus. The power bus goes to your meter (so you can be billed). The meter is connected to a power distribution transformer. The PDT is connected to a single phase of local power distribution lines. The distribution lines travel down to the local utility substation, where they connect to its own bus, transformers, and subtransmission lines.

The substation is a cause of flickering, although a different type. Some substations have battery holds, while others have whole generators for the same purpose: act as a buffer while the switches open due to a power event, or wait for the upstream generator to spin up to meet demand.

But during a lightning storm, a lightning strike along the lines will trip the breakers at the substations – which are the autoreclosing type. Once the breakers trip, the substation’s backup power goes into effect, until the breakers automatically reclose. The brief delay in power transfer can cause lights to visibly flicker during the changeover, as well as when the breakers reclose (notice how flickers always come in pairs during heavy storms).

A branch falling on the lines somewhere or another short circuit can also cause this.

Of course, once the backup power runs out or the maximum amount of reclosures is reached for the breakers, it’s lights out for the distribution customers branching off that substation.

Wrapping up

So those are all the possibilities for light flickering in bulbs. Some are more complex than others, ranging from quantum electron effects to simply shaking a bulb – but the end result is all the same.

Any other ideas or questions? Quantum physicists to elaborate on the effect described? Leave a comment!