MD-631 Xenon Lamp
Continuing my series of posts of Xenon light sources, today I’m posting a few pictures of a Ceramic Xenon lamp as used in the endoscopy light source previously posted. The construction is pretty simple, but these lamps are well engineered and surprisingly expensive ($200+).
You can see how the lamp is connected to power from the image above. Each end of the lamp is a terminal seperated by a ceramic tube. The startup voltage for these lamps is in the 20kV range, so the terminals need to be reasonably well isolated and able to withstand the high pressure Xenon gas. Ceramics work well for this.
The glass window is surprisingly thick (3mm). This is required to withstand the high pressure of the Xenon gas in the lamp. Wikipedia also suggests fused silica is used, due to its ability to withstand higher pressures than standard glass. If this is the case, it would explain some of the cost, as fused silica tends to be significantly more expensive than borosilicate glass. It would also mean that the window is transparent to UV (which standard glass isn’t). At some point, perhaps I’ll stick the window in my UV spectrophotometer and we can see how well it blocks UV.
Xenon lamps tend to output significant amounts of UV light… but if other components are not-transparent to UV (regular lenses) they’ll effectively be operating as filters anyway. It would be interesting to see if this particular bulb outputs UV though. Xenon flash lamps are often used in UV-Vis spectrophotometers, and these lamps might make an interesting alternative for use in some of the spectrophotometer hacks I’ve played around with.
Inside the lamp, we can see the electrodes themselves:
The electrodes themselves apparently contain Thorium, and so are probably best treated with care. As you can see above, the electrode comes to a point, I assume this is to help confine the discharge/create a strong localized field.
This sits over the anode, which is placed in the center of a parabolic reflector. Persumably the parabolic reflector focuses the light at some fixed point outside the bulb.
This lamp had obviously failed, and it would be interesting to know exactly what happened. There’s an interesting document here which discusses potential failure modes. It suggests that failure is usually down to the anode becoming damaged. The anode is exposed high temperatures and currents and eventually it’s just going to break down. It would be kind of interesting to compare new and old anodes. If I ever come across a lamp which has failed near the beginning of its lifetime (maybe due to a leak/physical damage), I’ll be sure to take some pictures for comparison.