How Do Neon Signs Work? Gas, Glass and High Voltage Explained

A neon sign works by passing a high-voltage current through a sealed glass tube that holds a small amount of gas at very low pressure. The electricity strips electrons loose and sends them racing through the gas; when they collide with gas atoms, the atoms absorb energy and release it again as light. Pure neon glows a warm red-orange. Every other colour comes from a different gas, a coating inside the tube or tinted glass.

The physics is the easy part to describe. Making a sign is a hands-on trade that mixes glassblowing, vacuum work and electrics.

What is inside a neon tube?

Each lit line of a sign is its own sealed circuit, made of four parts:

• The glass tube. Usually lead or soft glass, shaped into letters or outlines.
• Electrodes. A metal shell sealed into each end, with a wire lead that connects to the power supply.
• The gas fill. Neon, argon or a mix, at a pressure far below that of the air around us.
• The power supply. A transformer or electronic unit that steps ordinary mains power up to the several thousand volts needed to start and hold the glow.

The low pressure is essential. At normal air pressure the gas would not conduct in this way; with most of the gas removed, electrons can travel far enough between collisions to build up the energy that makes atoms light up.

How are neon signs made?

Production follows a fairly fixed order, and most of it still happens at a workbench.

1. Pattern. The design is drawn full size, reversed, on a heat-resistant sheet. The bender works on the back of the lettering, so the finished face reads correctly.
2. Bending. Straight tubes are heated over gas burners of different shapes until a section softens. The bender shapes it to match the pattern while gently blowing through a tube to keep the glass from collapsing at the bend.
3. Blocking out. Parts of a tube that should stay dark, such as the joins between letters, are painted with an opaque coating.
4. Electrodes. An electrode is welded onto each end of the shaped tube.
5. Bombarding. The tube is attached to a vacuum manifold and the air is pumped out. A heavy current is then passed through it to heat the glass and electrodes, driving off moisture and impurities that would shorten the sign's life.
6. Filling and sealing. Once the tube is clean, a measured amount of neon or argon is let in and the tube is sealed off from the pump.
7. Ageing. The new tube is run for a while so the glow settles and becomes even before it is mounted.

Where the colours come from

Only the red-orange tubes are strictly neon. The rest rely on a few tricks, often combined:

Because tubes containing mercury cannot simply go in household rubbish, old or broken ones should be handled as hazardous waste under local rules.

Neon versus LED neon

Many signs sold as "neon" today are LED flex: strips of small LEDs inside a silicone diffuser that imitates the look of a glowing tube. The two differ in practical ways:

• Look. Glass neon glows evenly all the way around the tube, with a softness that is hard to copy. LED flex is brightest from the front and can show faint dots up close in cheaper versions.
• Voltage. Glass neon runs at high voltage and needs a specialist to install and repair. LED flex runs at low voltage and usually plugs into a simple adapter.
• Durability. Glass is fragile and heavy to ship; LED flex bends and survives knocks.
• Repairs. A broken glass tube can often be remade by a bender. LED strips are usually replaced as a section.
• Effects. LED flex can change colour or dim easily; glass neon is a fixed colour per tube.

Signs of trouble

A neon sign can run for many years, but a few symptoms point to a problem:

• Flickering or a dim tube can mean a gas leak or an ageing power supply.
• A loud buzz often comes from the transformer.
• Colour turning pinkish or patchy in a tube that used to be even can point to contamination.
• One section dark may mean a broken tube or a loose connection.

Because of the voltages involved, repairs are not a do-it-yourself job; switch the sign off and call a sign maker.

Neon in the street scene

For shops, bars and cinemas, a lit sign is part of how a frontage invites people in after dark. It sits alongside the other parts of a welcoming shopfront, such as the retractable awnings that add shade and curb appeal. At home, the glow of a small neon or LED piece works best as an accent rather than the main light, layered with the kind of recessed can lighting found in contemporary rooms. And if you enjoy the craft behind everyday objects, our step-by-step look at how vinyl records are made follows another analogue process that has outlived predictions of its end.