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Why Are Incandescent Bulbs Very Inefficient And Burn Out Quickly?

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.

Incandescent bulbs are extremely inefficient because 90% of the energy is wasted as heat, with only 10% being converted to visible light. 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 every time the bulb is turned on.

How Does The Incandescent Bulb Work?

Did you know that incandescent bulbs are over a decade old?

That’s right, incandescent bulbs were first invented in 1879 by prolific scientist and inventor, Thomas Edison.

After thousands of experiments testing everything from platinum to coconut fiber, Edison filed a U.S patent for an electric incandescent lamp that uses “a carbon filament or strip, coiled and connected to platina contact wires.”

So how does it work?

Edison’s bulb consists of a thin carbon filament located inside a glass vacuum bulb. The filament itself is thinner than a strand of hair and is coiled into a spiral shape.

When an electric current is passed through, the filament acts as a black body radiator. Essentially, the electricity gives extra energy to the atoms of the filament. But this causes the atoms to become unstable.

Because they don’t know how to respond to this newfound energy, the atoms drop to lower energy again. To do this, they release the extra energy in the form of photons, also known as light.

In simple terms, electricity heats the filament until it glows and gives off light.

Got it?

Interestingly, though incandescent bulbs have had minor tweaks and upgrades, not much has changed since Edison’s days.

The main upgrade is the addition of inert gases such as argon and nitrogen to the glass bulb. This is intended to minimize the evaporation of the filament and prolong the lifespan of the bulb.

Heat vs Light Output: How Much Heat Does Light Bulb Generate?

incandescent bulb turned on

Now that you understand how incandescent bulbs work let’s talk about their efficiency. Or should I say inefficiency?

For years, incandescent bulbs were praised for being the cheapest lighting fixtures on the market. But this came at the cost of horrendous inefficiency.

Incandescent bulbs are not very good at knowing what to do with the electrical energy they’re supplied.

Around 90% of an incandescent bulb’s electricity supply is wasted as heat, with a measly 10% actually being used to create light. This is because the tungsten filament inside an incandescent bulb needs to be heated to around 4600 degrees Fahrenheit to produce light.

The inefficiency of incandescent bulbs is often expressed in the form of luminous efficiency. This is a measure of how well a light source produces visible light. It is calculated by dividing luminous flux (amount of light) by radiant flux (overall amount of energy emitted).

Most incandescent bulbs have a luminous efficiency rating between 2 and 3 percent. For comparison, LEDs typically stand between 5 and 20 percent.

So as you can see, incandescent bulbs have a lot of room for improvement.

This is a good example of one of the fundamental laws of physics, the conservation of energy. This principle states that energy cannot be created nor destroyed. It can only be transferred from one form to another.

When a 100-watt lamp is turned on, 100 watts of electrical energy is converted to 100 watts of light and heat. As incandescent bulbs are incredibly inefficient and have a luminous efficiency of 2-3%, this usually translates as 98 watts of heat and 2 watts of light.

In this sense, incandescent bulbs are more efficient as heaters than they are as light sources. More on that later.

But as global interest surrounding global warming and green energy has grown over the last two decades, incandescent bulbs were quick to come into the firing line.

Nowadays, most countries have prohibited the manufacture, distribution, sale, and use of incandescent bulbs. Amongst these is the European Union, Australia, Canada, Russia, and the United States.

According to Green Tech Media, the restrictions have resulted in global sales of incandescent bulbs falling from 12 billion to 2 billion units per year. It’s also estimated that the regulations will reduce CO2 emissions by up to 15 million tons a year!

In place of incandescent bulbs, most countries promote the use of CFLs or, even better, LEDs.

Why Do Incandescent Bulbs Burn Out?

filament light bulb

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!

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.

Also read: Will LED Bulbs Melt Plastic Fixture?

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

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 You Heat Up The Room With Incandescent Bulbs?

Now let me share something interesting with you. As I was writing this article I became extremely interested in knowing whether the incandescent bulb can heat up a room.

When I was a kid we had a fixture in a room with incandescent bulb and it was so hot that I could felt it from the opposite side of the room, and this is why I am now so curious to figure that out.

As I said earlier the temperature of the traditional bulb is extremely high. This immense amount of heat can warm up the surrounding atmosphere, much like a radiator. This is why incandescent bulbs are often used in things like incubators and reptile habitats.

So back to the question at hand, yes, an incandescent bulb can heat up a room. But whether you should use incandescent bulbs as a heat source is another question.

In any case, the temperature increase produced by an incandescent bulb will be relatively minor. It may help to lower your heating bill a tiny bit, but there are much better ways to keep yourself warm.

Furthermore, an incandescent bulbs ability to increase room temperature is affected by several variables:

  • The bulb’s wattage.
  • The size of the room – Incandescent bulbs will heat small rooms better than big rooms.
  • The room’s ventilation – Rooms with good ventilation will be harder to heat.
  • The location of the room – Heat rises, so attic rooms will be more susceptible.
  • The number, size, and thickness of any windows.
  • The color of the walls.
  • The outside temperature.

How Long Does It Take To Heat A Room?

high temperature

An incandescent bulb emits 90% of its energy as heat and 10% as light. Therefore, a 60W bulb emits 54 watts of heat and 6 watts of light.

But watts represent the power consumption of the bulb. Thermal energy (heat) is better quantified in Joules (J).

One watt is equal to one joule per second. So a 60-watt bulb uses 60 joules of energy per second.

Therefore, using a 60-watt bulb for 60 seconds produces 3,600 joules of heat energy.

Are you following? Good, then let’s carry on.

Let’s imagine your room is 15-foot x 20-foot x 10-foot. This equals 3000 cubic feet or 84.95 cubic meters.

The volume of air in the room is 84.95 cubic meters x 1.2kg/m3 (density of air). This equals 101.94kJ.

To increase the temperature of a substance by one degree, you need to know its specific heat. The specific heat for air is approximately 1 kJ / K*kg.

So it would take approximately 101.94 kJ of energy to heat the room by 1 degree.

The 60-watt incandescent bulb produces 3,600 joules of energy per minute. Therefore, it would take 28 minutes (102,000 kJ / 3600 J) to increase the room temperature by 1 degree.

This of course is under the condition that no one enters the room and heat has nowhere to escape.

How To Safely Handle Burned Bulbs?

broken incandescent bulb

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?