Picture of a green glowing neon money sign lamp, featuring mercury vapor gas, blue based fluorescence.

What is the Color of a Neon Light

Question: What is the Color of a Neon Light?  Answer: As in just about all gaseous discharge lamps, they establish the color that neon lights glow by manipulating several factors, including:

    1. The type of gas inside the neon light’s glass tubing.
    2. The amount gas (pressure) inside the tube.
    3. Also, the type of fluorescent coating on the inside surface of the tubing.
    4. The color of the glass tubing itself.
    5. Combinations of the above factors can produce colors in neon lights that span the entire visible spectrum and beyond.
    6. Plus, to a much lesser degree, the amount of voltage applied can affect the emitted light color.

What is the Color of a Neon Light

For an explanation of each of these color-determining factors, see below.

1. The Type of Gas Helps Set the Color of a Neon Light.

There are primarily two colorless, odorless gasses used in this form of gas discharge light: neon (of course) and mercury vapor. Plus, they use several other gasses as well, either separately or in combination, to control what color you ultimately get from a neon light.  These include hydrogen for a deep red light, helium for yellow, mercury in the blue-based neon lamps and signs, and, though seen infrequently, carbon dioxide for white light.

Furthermore, even though the mercury vapor, hydrogen and other gas discharge lights contain no neon, we still collectively refer to them all as ‘neon lights’. Why?  Because they bear most of the same functional characteristics of neon lights, except that they contain other gasses and gas combinations besides neon.

Mercury vapor, when placed inside a clear, non coated glass tube, and subjected to a couple thousand volts of electricity, glows a sort of gentle blue color. You can see this shade in street lights when they first come on and they are still very dim.

On the other hand, use neon gas, and you get a fiery, coal red glow such as seen coming from neon light beer signs. Neon requires higher voltages to create and sustain ionization in the colorful neon light.  Further, the amount of voltage required to get a healthy red glow from neon depends on the pressure of the neon gas inside as well as the length of the tube. A five-foot long tube filled with neon requires about 7000 volts to glow.  Red base neon lights contain neon, while blue base lights have mercury vapor.

Neon dollar sign lamp, turned off. No color filter glass here. It only shows green when it's operating.
Neon dollar sign lamp, turned off. No color filter glass here. It only shows green when it’s operating.

2. The Amount of Pressure Affects Color of Neon Lights

The pressure of the gas in the glass neon light tube is crucial. Too little pressure, too much air, or too much vacuum, and you’ll need prohibitively large amounts of voltage to get the gas to ionize, conduct current,  and glow. On the other hand, put too much gas in, and neon loses its vivid red color when ionized, and becomes more of a pink or white. To get good color and solid flicker-free lighting, you must control the pressure very precisely.

3. The type of Fluorescent Coating Affects What is the Color of a Neon Light

Neon lamps did not earn their colorful, vibrant reputation by using clear tubes of glass filled with neon gas alone; at least, not at the beginning. Without other mechanisms, the only colors you’d have would be red (neon) and blue (mercury vapor).

But neon lights come in just about every color of the rainbow, via the employment of the principle of fluorescence. Have you ever seen those brightly colored paints at Spencer’s gift shops that, when placed under a black light, glow unusually brightly? These are fluorescent paints, because they have the ability to absorb light energy of one color or wavelength, and convert it to another color. These paints convert the near ultraviolet rays of a black light into visible light. This makes them appear to glow without external stimuli. And that makes them intriguing to us younger folk. 🙂

On the other hand, they create similar effects with neon in the tube. Neon produces a fair amount of infrared light that can they can also convert into visible energy as well. Pink is probably the most popular color we get using the neon gas and fluorescence combo inside a neon light.

Picture of a red neon musical note artistic lamp turned on. Showing the light emitted from red-based neon / hydrogen gas mixtures from within clear glass tubes.
Red Neon Musical Note Artistic Lamp, turned on. Showing the light emitted from red-based neon / hydrogen gas mixtures from within clear glass tubes.

4. Coloring the Glass Tubes Affects Color

When colored, the glass tubing Itself also Influences the emitted light color. This form of light filtration appears in incandescent Christmas light bulbs of past decades, to shine the popular reds, yellows, greens, and blues of the holiday season.   As with the Christmas lamps, manufacturers apply a transparent or translucent coating to the outside of the glass. This filter prevents all but the color of light they want to pass through. So it is with neon lights.

In neon, you might start with a white light, and apply a nova blue filter to the glass, for a really bright, deep blue light. The extra bright neon that has appeared over the past 20 to 25 years employs this method. You can recognize this when the light is off. If the tube has color, something other than white, then this filtration system is its mode of operation of the neon light. A white tube means that method 3 is how the color appears when you turn on the lamp.

5. Coating Inside of Tube with Fluorescent Chemicals Changes Color Output

Technicians can produce combinations of the above By applying a fluorescent coating to the inside of the tube. They also might add a filter to the glass itself or to the outside of it.  Thus in this way, they can create all the visible colors in a wide array of intensities.

6.  Applied Voltage Affects What the Color of a Neon Light Is

On voltage determining neon light color: The voltage level controls more the intensity of the light rather than its color.  However, be careful not to apply too much voltage, as this can alter the chemical makeup of the neon and render it incapable of producing any light at all.  I experiment with those little neon light bulbs that you see in elevator button panels, old radios and so on.  I found that excessive voltage makes them glow quite brightly for a short time.  But they then burn out.

Picture of the musical note lamp turned OFF. No sign of red in either the clear glass or gas inside.
The musical note lamp turned OFF. No sign of red in either the clear glass or gas inside.

It appears however, that LED-filled tubes are supplanting gaseous discharge neon and fluorescent lights, because they require less voltage, are easier to fabricate, are more rugged and thus, are harder to break, are more efficient, and the LED lights are fast becoming cheaper than true neon lights, though they faithfully duplicate the brilliance and vibrancy of neon lights.  Plus, you can adjust LED lights in a neon-style configuration to emit any color in the rainbow.  But thy set the light color in traditional neon lights at the factory. So you cannot easily change it.  Still the transition from neon to LED is slow at present.  So true neon lights will be popular for some decades to come I suspect.  Long live neon lights.  I love ‘em!

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    1. Neon Signs (Examples of Neon Lights)    on Wikipedia
    2. What is Neon Lighting?   on Wikipedia