Why Do Incandescent Bulbs Burn Out?

Have you heard the story of the longest-lasting bulb?

It is a handmade carbon filament incandescent bulb manufactured in Shelby, Ohio. It has been burning almost continuously since it was turned on in 1901. That is a whopping 119 years in 2020.

It has also been featured in the Guinness Book of World Records, and Ripley’s Believe It Or Not!

Remarkable as that story is, it is one of a kind. Your personal experience of burning out bulbs will probably tell you another story altogether.

In practice, incandescent light bulbs generally have a lifespan of about 2000 hours, which means that they will last less than one year based on a 6-hour use every day.

The reason an incandescent bulb burns out is due to eventual thinning of the tungsten filament that burns white hot, to give off light. Compounding the issue is excessive surge current that passes through the filament everytime the bulb is turned on.

Too Much Current Going Through The Thin Filament

A traditional incandescent bulb is made of the glass casing, and the tungsten filament placed right at the center.

This tungsten filament is made of very long but thin wire, originally almost 2 meters long, coiled over and over again, eventually measuring only about 3 cm to fit into the small space of the bulb.

Now, if you remember your science lesson, the reason a bulb lights up is that current passes through a thin metal wire, making it turn white-hot, and as a by-product of this heat, visible light is also given off.

When a metal is cold, it has very little resistance to current, which means that the metal allows a lot of current to pass through, even more than is safe for the metal.

Putting it all together, here is the exact process by which an incandescent bulb will suddenly fail or stop working. This will most likely happen when you turn it on:

When the bulb is off, the tungsten filament is cold and thus has very low resistance. When the bulb is turned on from a switch, the current starts going to the thread.

As the resistance is quite low, in the tens of Ohms, the filament lets through a massive surge of current, also called, you guessed it, ‘surge current,’ the bane of electronics.

Within the next few milliseconds, the filament heats up instantly, raising the resistance of the metal filament to the range of some hundreds of Ohms.

So the current passing through reduces down to the normal amperes.

Now, if the bulb is new and well made, with a thick enough filament to withstand such surges, and the tungsten has not weakened due to use over time, the bulb will continue operating as usual, giving white-hot heat and light.

However, we are looking at catastrophic failures!

Over time, the tungsten atoms are used up by incandescence, where the tungsten atoms literally change from solid-state to the gaseous vapor state.

This gradual evaporation of the filament obviously weakens it from here and there.

One beautiful day, as the bulb is turned on, an enormous rush of current passes through, but this time, it instantly burns the weakened tungsten filament, and the bulb shuts off, for good.

Once you think about the fact that in milliseconds, the metal goes from room temperature to about 3000°C (5400°F) with negligible resistance to high current on top of that, you start to wonder why incandescent bulbs don’t burn out every time they are turned on!

Why Do Incandescent Bulbs Keep on Burning In The Same Socket?

Has buying a new incandescent bulb become a monthly shopping item for you?

Perhaps you have this one particular socket. Maybe it is part of a chandelier or a multi-bulb floor lamp, but every time you put a bulb into that ONE specific socket, it burns out much faster than the others have.

Don’t worry, nothing spooky there, most likely bad wiring.

What causes this to happen is that the bulb is not getting a solid stream of electricity. The points in the electrical line where this can happen, are numerous:

The socket: A socket can become worn out over time, as bulbs get screwed in, sometimes too tightly, eating away at the soft metal soldering and insulation little by little. This means the bulb is not solidly sitting in the socket.

The switch: Inside the switch is a whole bunch of wiring of its own. A poorly made switch or an old one might have a problem inside it that translates into a faulty socket, and thus a defective bulb.

Wiring: The wiring connecting to the switch from either end could be loose, and loose connections can be really bad for bulbs as they cause constant electricity fluctuations, vibrating the delicate filament constantly, causing it to weaken quickly.

Can Burned Out Incandescent Bulbs Cause Fire?

burned out light

Did you know that paper can start to burn at around 240°C (464°F)?
And if you read carefully the section above, the temperature inside an incandescent can reach around 3000°C (5400°F). Doesn’t take much science to figure out that filament bulbs that are not used correctly can absolutely and have caused house fires in the past.

A few basics of using bulbs correctly will keep you safer than not knowing the dangers.

An overheated fixture due to lack of air ventilation or due use of a higher than advised wattage bulb can cause the socket to burn out, melting the components, and eventually
causing a fire.

Enclosed fixtures like glass globes are especially susceptible to getting heated up.

How To Safely Handle Burned Bulbs?

Considering you still have incandescents installed in your home or office, it may not be long before they burn out.

Once they burn out, follow these instructions to make sure you don’t hurt yourself or anyone else as you get rid of it. It is also possible the bulb might crack and break as you take it off.

Hold back on your instinct to quickly pick up the broken bulb. The glass and metallic parts will be quite hot. If you can, give it a few quick seconds to cool off.

Turn off the switch, and if it is a table or floor lamp, also unplug the wire from the wall to be extra cautious.

Using oven gloves, take off the bulb, and safely put it into a plastic bag before tossing it into the garbage bag, to prevent waste handlers from injuring themselves.

If your bulb is intact, you can safely attempt a few Pinterest hacks on upcycling the glass bulbs as trinkets holders, or mini terrarium globes.

Then you can artistically preserve and display for future generations the antique technology that are tungsten filament bulbs!

Final Word

If you are waiting for your incandescent bulbs to burn out, so you don’t create waste, keep this guide handy. You now know the reasons as to why filament bulbs burn out.

Have you shifted to LED bulbs in your home and office?

What is the longest your incandescent bulbs have lasted?

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