What You Need to Know About Flash Lamps

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We mostly hear the name xenon flash lamp being thrown around, but we’re not really sure what exactly a xenon flash lamp is. To put it simply, a flashlamp is an electric arc lamp designed to produce extremely intense, incoherent, and full-spectrum white light for very short durations. These lamps are made of a length of glass tubing with electrodes at either end and are filled with a gas, in this case, xenon, which when triggered ionizes and conducts a high voltage pulse that will produce the light.

How Are They Made

As mentioned, flash lamps are made of a hermetically sealed glass tube, which is filled with xenon, and electrodes to carry electrical current to the gas. In addition, they do need a high voltage power source that will energize the gas and a charged capacitor to supply energy for the flash. The flash lamp is made up of three main parts; glass envelope, electrodes & seals, and gases and fill pressure. The glass envelope is basically the outer structure that encloses everything. The electrode is the part that conducts the electricity and heats up to produce the light required. The gases are the material that gets ionized, in this case, xenon. The reason why xenon is mostly preferred is because of its high efficiency, where it converts 50% of electrical energy into light.

How To Operate a Flash Lamp

The electrodes of the flashlamp are usually connected to a capacitor, which is charged to a high voltage of between 250 to 5000 volts using a step-up transformer. However, the gas tends to have a high amount of resistance, making the lamp not conduct electricity until the gas is ionized. There are a few methods to ionize/trigger the gas.

  • External Triggering. This is, without a doubt, the most common method, especially for photography use. It is quite a complicated process but to put it simply, the electrodes are charged to a voltage high enough to respond to triggering but below the lamp’s self-flash threshold. An extremely high voltage pulse is then applied directly or very near to the glass envelope. This pulse creates an electrostatic field, which then ionizes the gas inside the tube.
  • Series Triggering. Though rare, this method is most commonly used in high powered water-cooled flashlamps such as the ones found in lasers. In this method, the high-voltage leads of the trigger-transformer are connected to the flash lamp in series. This way, the flash travels through both the transformer and the lamp. The trigger pulse then forms a spark inside the lamp without exposing the trigger voltage to the outside of the lamp.
  • Simmer- Voltage Triggering. This is the least common technique. When using this method, instead of initially applying the capacitor voltage to the electrodes, a high voltage spark streamer is maintained between the electrodes. The high current from the capacitor is delivered to the electrodes using a thyristor or a spark gap, and voila!

The intensity and duration of the flash lamp entirely depend on the method of triggering as well as other factors such as power efficiency.