Demise of a Flashtube

Here at Beau Photo, we have many studio strobes to choose from in the Rental Department. From the economical Photogenic to the cream of the crop Profoto, they all have one thing in common – the flashtubes will eventually wear out. How does one know if the flashtube has worn out, you ask? The most obvious answer is the flash does not fire, but there are other ways to tell if your flashtube is nearing the end of its useful life.

When a flashtube is nearing the end of it’s life, it will start misfiring at lower power levels and it will get worse until it does not fire at all even at full power. When you start to notice the strobe not firing at intermittent intervals you will know replacement is imminent. The flashtube in this article is a Hensel flashtube that has failed due to a combination of factors. (Cover photo)

Another less obvious way is to look at the ends of the flashtube and see if the glass is developing micro-cracks or is getting darker or black on the inside. The cracks develop due to sustained high power levels pushed through the flashtube, where the intense heat of the flash pulse heats the inner wall of the tube, but the outer wall is still cold (Picture 2). The glass can even warp and form microscopic bubbles as shown in Picture 3. The cracks will eventually release the xenon gas in the tube, rendering it useless.

There are two different types of a more gradual failure. These are called ‘sputter’ & ‘ablation.’ Sputter is the vaporization of the metal from the cathode of the flashtube, which is then deposited on the inner wall of the flashtube, reducing the light transmission. Ablation is when the electrical arc erodes the inner wall of the flashtube forming a cloudy appearance. The ablation releases oxygen from the glass, increasing the internal pressure beyond an operable level. A combination of ablation & sputter can be seen in Picture 3.

*Some information taken from Wikipedia*

Picture 2

Micro-cracks in the glass wall of flashtube.

Picture 3

Part of flashtube next to the cathode showing micro-cracks, bubbling, warping, ablation & sputter.

Picture 4

Clean anode.

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