Spectra of starter lamps from fluorescent lamp starters

Challenging measurements with simple means: Practical task for beginners and advanced learners

Who would have thought that an inconspicuous fluorescent lamp starter could conceal a whole treasure trove of interesting light sources? So-called starter lamps are built into the small glass tubes that serve as ignition aids. They work on a simple principle: as soon as voltage is applied, the gas inside begins to glow—emitting a characteristic emission spectrum.

These starter lamps are not only crucial for the functioning of fluorescent lamps, but also provide an exciting field of experimentation for lighting technology and spectroscopy. With a DIY spectrometer, the different light colors and spectral lines can be made visible, illustrating the interaction between gas discharge, light emission, and electrical voltage.

For technology enthusiasts, physics students, and anyone interested in light sources and spectral analysis, starter lamps offer a surprisingly easy introduction to the fascinating world of light and spectral research.

Practical tip: Safe control of starter lamps

For experiments, starter lamps do not need to be operated with mains voltage. They can be easily operated with inverters for EL foils.

• Such inverters operate with a safe input voltage of, for example, 5 V DC.
• At the output, an additional series resistor is sufficient to limit the current so that the glow discharge ignites, but the bimetallic electrodes are not heated to such an extent that they deform and cause a short circuit.
• The outputs of the inverter, the series resistor, and the glow lamp must, of course, be protected against contact, as the operating voltages here exceed 100 V.

This transforms a »waste product« such as the lamp starter into an inexpensive, easily accessible light source for spectroscopic investigations.

Three variants – three very different spectrums

We rummaged through our junk box and salvaged various old starter lamps. The result? Three completely different color moods:

• types with a cool, almost mystical violet-blue glow;
• types with a strong, warm orange-red that immediately catches the eye;
• and finally, versions with an exciting mix in which both colors merge together.

It's obvious to the naked eye: there's more to it than you'd expect from an inconspicuous starter. Now for the reveal—our DIY spectrometer shows which gases are really behind these colors …

The mystical violet blue

To the naked eye, the glow appears almost mysterious—cool, intense, and somewhat extraterrestrial. But the DIY spectrometer quickly provides clarity: distinct peaks between 400 and 500 nm reveal the signature of argon. Thanks to the NIST database (Atomic Spectra Database | NIST)). ¹, these lines can be clearly identified—transforming the mystical glow into a clear fingerprint of the gas.

The fiery orange-red

As soon as it is switched on, the small starter lamp glows in a warm, intense red-orange—almost as if a piece of sunset had been captured. But here, too, the DIY spectrometer reveals the secret: strong peaks around 585 nm and 640 nm match perfectly with the typical emission lines of neon, which can be clearly found in the NIST database (Atomic Spectra Database | NIST) ¹.

If you look even closer, two faint lines suddenly appear that clearly belong to xenon. A small surprise effect, but what is behind it? Are these tiny impurities in the filling gas, or perhaps even an intentional admixture? That remains unclear—but it is certainly intriguing.

The mysterious play of colors

The glow of this starter is unusual, a fascinating mixture of cool blue tones and warm orange. What appears to the eye as an atmospheric play of colors is broken down into its components by the DIY spectrometer: superimposed peaks of argon and neon reveal a gas mixture that combines both worlds in one lamp. A beautiful example of how spectroscopy reveals hidden details.

Here we show a spectrum with an integration time of 1 s, in which the strongest argon lines are easily identifiable.

However, with an integration time of 3 s, many more weaker lines appear, especially in the range between 400 and 500 nm. The sensor reaches saturation with the stronger argon lines, which can be seen from the distortions in the upper signal range. However, this does not interfere with the detection of the weaker lines.

¹ Kramida, A., Ralchenko, Yu., Reader, J., and NIST ASD Team (2023). NIST Atomic Spectra Database (ver. 5.11), [Online]. Available: https://physics.nist.gov/asd [2024, June 23]. National Institute of Standards and Technology, Gaithersburg, MD. DOI: https://doi.org/10.18434/T4W30F