Science, Maths & Technology

How neon lights

Updated Friday 6th July 2007

Find out how neon lights the sky up at night

Look at the glow from a neon striplight and what you are seeing is the light output of billions of individual neon atoms. Neon produces this light because it is being held in the form of a plasma.

You might remember learning that there are three states of matter: solid, liquid and gas. It’s much less common to encounter the fourth state, which is plasma; yet 99.99% of the matter in the observable universe exists in this form.

The Sun [Image: NASA/JPL] Copyrighted image Icon Copyright: NASA/JPL For example stars, like our Sun, are composed of plasma.

What is a plasma?

Atoms are normally electrically neutral, consisting of identical numbers of positively charged protons and negatively charged electrons. In a plasma some of the electrons have been separated from their atoms and are free to wander. The atoms which have lost an electron (these are referred to as ions) are still present and preserve the overall neutrality of the plasma.

Atoms, electrons, ions Copyrighted image Icon Copyright: OU
Atoms showing atoms in green, with electrons in blue and ions in red.

In a star, the separation of the electrons is achieved through heating. However, it is possible to make a plasma that is cold. The presence of free charges means that, unlike a gas, a plasma will conduct electricity. In fact the plasma is formed and preserved by placing a voltage across the gas.

The presence of a voltage causes the free electrons to be accelerated, and they collide with neutral atoms turning some of them into ions, thus sustaining the plasma.

What causes the plasma to glow?

Many of the collisions between atoms and electrons don't result in ionization. Instead, some of the energy from the collision is absorbed by the atoms before being swiftly re-emitted as invisible ultra violet rays and visible light with colours that are specific to the particular species of atom.

This is what you see when you look at a neon lamp. The distinctive orange-red colour of the glow from neon is a characteristic of the element neon, other gases, such as argon, would glow with a different colour.

This is not the whole story; the tubes that James examined in the TV programme are coated with a material that 'fluoresces', converting invisible ultra violet into visible light. By doing this it is possible to vary the colour of the lamp, but that's another story...

 

For further information, take a look at our frequently asked questions which may give you the support you need.

Have a question?

Other content you may like

Challenge: Make an Underwater Torch Copyrighted image Icon Copyright: Production team article icon

Science, Maths & Technology 

Challenge: Make an Underwater Torch

The science behind making a torch that will work underwater, part of the BBC/OU's programme website for Rough Science 2

Article
article icon

Science, Maths & Technology 

Thermometer Challenge Glossary

Some of the key terms associated with measuring temperature

Article
Melting points Copyrighted image Icon Copyright: BBC article icon

Science, Maths & Technology 

Melting points

What can we tell by comparing melting points?

Article
Accurate weighing balance Copyrighted image Icon Copyright: Production team article icon

Science, Maths & Technology 

Accurate weighing balance

Instructions for making your own accurate weighing balance, one of the scientists' challenges on the BBC/OU series Rough Science 3

Article
article icon

Science, Maths & Technology 

Microscope Challenge Glossary

Some of the key terms associated with making a microscope

Article
Kathy's Carriacou diary: Sun & sea Copyrighted image Icon Copyright: Production team article icon

Science, Maths & Technology 

Kathy's Carriacou diary: Sun & sea

Kathy Sykes's Sun and Sea diary, from the BBC/OU series Rough Science 2

Article
Challenge: Record a Sound or Voice Copyrighted image Icon Copyright: Open2 team article icon

Science, Maths & Technology 

Challenge: Record a Sound or Voice

The science behind phonographs and sound recording, part of the BBC/OU's programme website for Rough Science 2

Article
Fundamental physics and the magnetic monopole Copyrighted image Icon Copyright: Dreamstime article icon

Science, Maths & Technology 

Fundamental physics and the magnetic monopole

David Milstead can't predict what might spin off from his research into magnetic monopoles but, just as splitting the atom led to the electronics revolution, he's sure that today's pure physics research will lead to tomorrow's everyday technology.

Article
Metal detector Copyrighted image Icon Copyright: Production team article icon

Science, Maths & Technology 

Metal detector

Outline of how to make a metal detector, one of the scientists' challenges on the BBC/OU series Rough Science 3

Article