Why Is Incandescent Bulb Very Inefficient Light Source?

Fifty years ago, if you needed a new light bulb, incandescents were the only viable option. They were cheap, readily available, and got the job done.

Nowadays, however, you’d be hard-pressed to find any incandescent bulbs stacked on the shelves of your local supermarket.

So what happened? What led to the rise and fall of incandescent bulbs?

Incandescent bulbs are extremely inefficient because 90% of the energy is wasted as heat, with only 10% being converted to visible light. This gives incandescent bulbs a luminous efficiency rating of around 2%.

Ultimately, incandescent bulbs perform better as heaters than as light sources. So it makes sense why many countries have taken steps to phase out and ban incandescent bulbs.

If you’re intrigued about how such a wasteful light source remained popular for over 120 years, stick around.

In this article, I’ll be covering everything incandescent: how they work, how much heat they produce, and the type of light they emit.


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.

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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?

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.

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.

Incandescent Bulb Emits Infrared Light

Earlier in the article, I mentioned that incandescent bulbs emit 90% of their energy as heat and 10% as light. Well, this thermal energy is most accurately defined as infrared light.

Infrared light is one of the most discussed sections of the electromagnetic spectrum. It sits just below visible light, which means that it cannot be seen by the naked eye. Instead, you and I feel infrared light as heat.

Can this be classified as another one of incandescent bulbs downfalls? I guess so, but this is dependent on context.

In specific scenarios, such as in food preparation and animal habitats, infrared light is extremely desirable. Without infrared, we wouldn’t have things such as lava lamps or reptile incubators.

If you’re looking for a standard energy-efficient light bulb, the infrared level produced by incandescent bulbs can be extremely annoying. But it’s important not to underplay the value that it has in certain situations.

Some manufacturers even produce infrared filters to put over incandescent bulbs. These help to maximize the infrared output and minimize the amount of visible light.

Final Words

All in all, it seems that incandescent bulbs are a thing of the past. Their abysmal inefficiency ratings mean they have no place in modern, green society.

In fact, the standards we hold light sources too are getting more and more stringent. In January 2020, the U.S set out that all bulbs must have an efficiency standard of at least 45 lumens per watt.

Before reading this article, were you aware of how inefficient, traditional incandescent bulbs are? Let me know your thoughts, leave a comment down below.

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