What is a Hollow Cathode Lamp?

M. McGee

A hollow cathode lamp is a light source primarily used for scientific purposes. These lamps don’t really exist outside of laboratory settings, meaning most people will have never seen one. Most of the time, a hollow cathode lamp is used as a method of tuning in specific light frequencies. These frequencies are used to examine the composition of materials and tune in light-based systems, such as lasers. Depending on the materials used in their construction, the gasses pumped into them and exterior influences, a hollow cathode lamp can shine in nearly any color of the spectrum.

Man holding computer
Man holding computer

The design of a hollow cathode lamp is very different from that of a standard light. The majority of these lamps consist of four main parts. An anode and a cathode take in power and release it, respectively. They are connected to a large glass tube which is filled with a substance called a buffer gas. This gas can be any form of inert gas, usually a noble gas like neon, helium or argon.

When power enters the lamp through the anode, it moves through the gas to the cathode. This begins to excite the buffer gas and it turns into plasma. The plasma bombards the cathode and induces a process called sputtering. This is when high-energy particles knock atoms off a solid object. These sputtered atoms and the plasma bounce around more and more, gaining energy.

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As the energy begins to dissipate, the materials begin to emit photons. These photons are the light generated by the lamp. Different materials give off different wavelengths of visible light. The spectrum of the photons may be analyzed to determine the exact composition of the gases and sputtered materials. This process may be used to analyze the composition of an unknown material or verify the existence of a substance within a sample.

In addition, a hollow cathode lamp may be used to tune in specific light wavelengths. When a light-based system is designed within certain parameters, the initial power usage and wavelength setups are often tested on one of these lamps before it goes to the light system. This is primarily a cost issue; the designed systems are often very complex and expensive, so parameters are tested on the less expensive lamps.

In this case, the hollow cathode lamp is set up to use the same materials used in the light-based system. As power flows through the lamp, the light’s wavelength is examined. As the power fed into the system goes up and down, the wavelength changes. By using this method, scientists are able to determine the exact power requirements and materials needed for the larger system before they actually construct it.

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