Light bulbs

Yep, simple right? The humble light bulb has played a pivotal part in our history and has changed considerably in recent years as energy-saving models are taking over. But how do they work?

What is it?

A sealed glass globe with a metal base and containing a metal element, known as the filament, which glows when an electrical current is applied to it. Used to provide light in darkness and to indicate someone having an idea in cartoons.

Why is it useful?

The light bulb fundamentally restructured society. Oil lamps, gas lamps and candles used large amounts of fuel producing small amounts of light, so it was incredibly difficult to work, read, travel or really do anything at night. The light bulb:

• began ‘nightlife’ as we know it today
• extended the working day and increasing the ability of workers to raise their standard of living
• enabled indoor industries like manufacturing and medical research to thrive
• extended careers that might have been cut short from failing eyesight, bringing greater experience and progress to a number of fields
• gave birth to the age of electronics.

Today the world is lit up like the proverbial Christmas tree … light bulbs even had an impact on our society’s traditions and rituals.

New York city lights (Source: hauteliving.com)

How does it work?

No idea …

While Thomas Edison tends to claim the glory in history lessons for inventing the light bulb, it was actually the result of nearly 100 years of research by a large number of very clever scientists – Edison merely commercialized it. An early pioneer of the original ‘incandescent’ light bulb was chemist Humphrey Davy, who passed an electrical current through a strip of platinum (the ‘filament’) and then between two strips of carbon to produce light in 1809.

The idea was that because platinum (and carbon) had a very high boiling point, it could be heated to glowing point without completely disintegrating. The problem was that platinum was prohibitively expensive at the time and even then, the filament didn’t last for very long.

70 years later in 1879, Edison and his colleague Joseph Swan managed to make a filament that lasted a whole 13.5 hours (!) and it wasn’t until 1906-10 that General Electric produced the first bulb using the metal tungsten, the light bulb we know today.

Incandescent light bulb (Source: HowStuffWorks.com)

Know a bit about it …

Much like burning wood produces some light but mostly heat, only 4-6% of electrical power used by incandescent bulbs is converted to light. The tungsten is burned off slowly and gets deposited on the glass, making the bulb dimmer – it can’t actually combust as there is no air inside the bulb, but it still degrades.

‘Halogen’ bulbs function much like incandescent bulbs but with one major difference. They contain gases called halogens (like chlorine, iodine & bromine) that react with the burning off tungsten and recycle it, depositing it back onto the filament. This makes the filament last much longer, it can be burn hotter and brighter, and the bulb stays cleaner for longer. They are much smaller globes than incandescent lights and can be dangerous to handle after use as they get incredibly hot.

Halogen light bulb (Source: Merriam Webster online dictionary)

Both halogen and incandescent lights waste an enormous amount of energy as heat though and they are being phased out in our energy conscious society.

The new light bulbs that are seen almost everywhere today run much cooler. The light isn’t produced by burning or super-heating anything, and these are ‘fluorescent’ bulbs and LEDs – light emitting diodes.

Fluorescent bulbs are traditionally tubular in shape, don’t have a filament and are opaque as they are lined with a ‘phosphor’ – that is, a chemical like phosphorus or neon that glows under ultraviolet light (UV). The tubes contain a gas (argon), a bit of mercury and some electrodes, so that when a current is passed through the electrodes, the mercury atoms start racing around the tube excitedly and giving off … UV light! Normally we can’t see UV light – it’s outside the visible spectrum for human eyes – but the phosphor lining cleverly converts the UV into visible light, called ‘fluorescing’. In fact, UV or “black light” bulbs are pretty much the same thing without the phosphor in the bulb, so any fluorescing material outside the globe, from clothing to teeth to some types of paint, lights up.  (See How Black Light Works for details)

Shoes ‘fluorescing’ under UV or black light (Source: OnlyHDWallpapers.com)

Much lower power levels are needed to produce light in fluorescent lights as the bulbs can capture UV light, unlike incandescent globes, and little energy is wasted on heat. However, since most people are used to the amount of power (measured in Watts) needed for incandescent bulbs indicating the brightness, fluorescent bulbs for the home are still labeled as ‘equivalent to X watts’ on the packaging.

11 Watts in a fluorescent globe is equivalent to 60 Watts in an old incandescent globe

All over it!

LEDs are remarkable little light bulbs and are becoming progressively more popular for home use, but they have been invaluable in electronics since the 1960s. LEDs are solid-state bulbs, rather than hollow with some compound inside that does the lighting. They are made of semiconducting material, which means that they conduct electricity but as electrons flow between materials, they can leak a little bit of energy in the form of light – the colour depending on the material. For many decades, low intensity red was the only available LED.

LED bulbs (Photographer: PiccoloNamek)

LEDs are small, operate at very low voltages, and have much greater lifetimes than their hollow counterparts – sometimes up to 100,000 hours – which means they’re perfect for embedding into circuit boards and other inaccessible places. They’ve also been used in aviation, displays such as on digital clocks and large outdoor screens, traffic lights, and in appliances to let people know when they’re turned on. Infrared LEDs are used in many remote controls for household devices and new LEDs are bright enough to light rooms and screens of tvs and mobile devices in particular. These LEDs are still quite expensive relative to other types of bulb but their lifetime outweighs the initial cost. 

For more information, see a range of pages on How Stuff Works