# Catastrophic lamp failures

#### icewolf08

##### CBMod
CB Mods
Last night during the show we heard an unusually loud gunshot like sound. It actually caused an actor to do a doubletake. It seemed too loud to be a lamp failure and we didn't notice any dark spots on stage. Well, guess what we found during channel check today:

This is the front of the lens tube and lamp from a Strand Century Axial 6x9

Here is the back of the lens tube

And the lamp

Needless to say, as the LD used every 6x9 and 36˚ unit in my inventory, we will have to come up with a solution for tomorrow's show.

TheTheaterGeek

#### Wolf

##### Active Member
what would have cause the lamp to fail like that, simple as just someone had touched it?

##### Member
Yeah...FELs go out with a bang. At our theatre here, we have an inventory of about 20 S4's and 30 Strand Lekos (Which use FEL lamps). Whenever the Lekos go out, everybody knows it. When the S4's go out, no flash, no sound, no nothing.

I just remembered:
I have a PAR64 lamp to replace this weekend because it went out this past weekend. It was really cool when it did go out, because suddenly this bright purple light filled the room.

#### Footer

##### Senior Team
Senior Team
I had one go out a few years ago in a 360q. It was during tech, so I was asleep in my office backstage. I hear the "shot", thought we were under attack. Then I get the page backstage saying we lost a lamp. I had to take the fixture down and completely tear it down to get all the glass out. We didn't break a lens though, thats a first time I have seen that. I have seen a Par56 explode... that was "cool"

#### icewolf08

##### CBMod
CB Mods
Most of my FELs have been replaced with HX-755s, but apaprantly I missed a couple (or at least one).

#### JD

##### Well-Known Member
Odd that the shatter pattern is from the front of the lens inward... Sure it wasn't really a gunshot?

#### icewolf08

##### CBMod
CB Mods
Odd that the shatter pattern is from the front of the lens inward... Sure it wasn't really a gunshot?
The shatter patter is on the inner of the two PC lenses in the tube, so it is from the back.

#### JD

##### Well-Known Member
The shatter patter is on the inner of the two PC lenses in the tube, so it is from the back.
Feisty little thing!!

#### derekleffew

##### Resident Curmudgeon
Senior Team
Alex, why does there appear to be about a 1/8" hole in the lens tube's right colorframe clip? Picture #1 also shows the silicone lens mounts not properly evenly distributed around the circumference of the lens.

I've only cracked the rear lens in 4 1/2 x 6 1/2 fixtures using FELs. (And 360Q-6x9, but that's wrong in the first place.) Such a catastrophic failure was most likely due to an impurity in the envelope, and not an inherent flaw in the lamp design. I have had HPL575s and 750s exhibit a similar end of life, but no cracked lenses.

Needless to say, as the LD used every 6x9 and 36˚ unit in my inventory, we will have to come up with a solution for tomorrow's show.
Buy a new 6x9 lens for $65, or hang a 6x12 approximately 1.5 times further away. #### icewolf08 ##### CBMod CB Mods Alex, why does there appear to be about a 1/8" hole in the lens tube's right colorframe clip? Picture #1 also shows the silicone lens mounts not properly evenly distributed around the circumference of the lens. I've only cracked the rear lens in 4 1/2 x 6 1/2 fixtures using FELs. (And 360Q-6x9, but that's wrong in the first place.) Such a catastrophic failure was most likely due to an impurity in the envelope, and not an inherent flaw in the lamp design. I have had HPL575s and 750s exhibit a similar end of life, but no cracked lenses. Buy a new 6x9 lens for$65, or hang a 6x12 approximately 1.5 times further away.
I never noticed the hole. I do the best I can with the manpower and budget I have to keep these fixtures running. They do pretty well, however, they have seen better days. I have done the best with the gear that I inherited when I took this job. Every year I take the worst of the fixtures out of service and replace them with Source Fours (about 4-10 each year depending on funds). Once out of my inventory, I give them to the Theatre Department here at the U. Most of them work very well despite the fact that they look like they have been Frankensteined together!

#### ship

##### Senior Team Emeritus
Or at least take these photos to those that do the budget and say you would like to go GLC or GLD for high output or GLA or GLE for long life with similar ouput. It's a safety issue as long as you don't tell them it's more of a fluke of filament failure and rare.

That's an amazing "Kill Roy Was Here" failure as I named such a thing when the filament of the lamp explodes out the side of the globe as if gunshot with the glass lingering in cooling as if held in slow motion in how it bent out to reflect the escape of the filament.

Most likely on the opposing side of the lamp you will also see a puckering of the glass as the gasses in the lamp were sucked out. This shape of the puckered/sucked in glass in the case of an incandescent lamp I noted with a filament gunshot thru the globe, formed a "Kill Roy Was Here" shape on the sucked in side of the glass. Thus the name for it I have.

Most likely, it wasn't due to touching the lamp as initially assumed, just normal halogen cycle in depositing tungsten particles on the hottest part of the lamp - the center of the filament, and for some reason as opposed to a normal failure, that filament in where it broke and going arc lamp or as I call "super nova", it flying out the side of the globe in that instant of while it's super nova. Given a halogen effect, that doesn't mean that spent tungsten particles near the edges of the hangers or lead in part of the resistant filament gets a re-deposit of tungsten on it as spent, instead it often just goes to the center of the filament in while it takes longer on halogen lamps to wear out than on non-halogen, incandescent lamps to wear out, still towards the filament supports or lead in wires of a halogen lamp, it can still wear out without replentishment. This area in a micro second often is also in normal and not shock where is where once broken an arch of current will develop until the resistance to current flow is too much to continue with that much brighter now in being a arc light intensity.

Given the power of that instance of it being an arc light, there becomes at some point so much pressure that there can be a blow out of the filament given all support and lead in wires for it have not had sufficient replentishment of them so as to support them while going super nova arc lamp as it were. At that point that filament resistor following the arc of current no doubt starts flopping wildly in explosion and should it escape during this also period of intense heat, that's about the end result. If nothing else, that's a lamp that lived well past it's expected lamp life if not got a shot of voltage in failing. Normal failure just under conditions where the amperage applied to it was sufficient to continue completing the circuit even if no longer connected to power source. Bang! within a micro second that filament escaped and the light goes out.

Rare and wouldn't be worried about happening, nor in this case it would seem did the fixture other than protect the audience or talent below as designed should it happen. Wouldn't tell the management it's other than a problem and we need to change lamps given the lamp in use, but realistically there was no safety hazzard. More just an excuse used to change to a better lamp.

The FEL ain't rated for most fixtures and even if rated for it, your's ain't efficient in using them as opposed to other lamps more recent to the market. It's a selling point for more efficient lamps budgeted for next year.

Go with it in selling it even if not normal to be a problem. In the end... Killroy Visited You as it were. It's rare and spectacular ain't it.

Get rid of them FEL's for other reasons than this filament spectacular escape.

Last edited:

#### mrb

##### Active Member
I bet this was a combination of factors, the lens not seated properly in the tube with the misplaced silicone pieces + tremendous heat from using 1K lamp = lens under stress, and the exploding lamp was enough to make the lens fracture. Kind of like how a piece of tempered glass under stress will explode with a gentle tap.

#### church

##### Active Member
unusual failure because these fixtures use two lenses with the curved surface touching. The 6*9 barrel actually uses two 6*9 lenses which at their centre are approximately 1.75 inches thick. However lenses used in stage fixtures include voids from the manufacturing process which don't affect their performance in this application. these voids in conjunction with stress from uneven lens mounting and even micro stress cracks from the fixture being moved and knocked may create the conditions for this type of problem.

If I was doing a failure analysis on this my hypothesis would be that as the shock wavefront resulting from the expanding halogen gas released by the rupture in the quartz envelope expanded through the focal gate and reached the first lens causing this lens to shatter and because there is only about 1/8 of an inch between the lenses one or more bits of gllass hitting the second lens causing it also to shatter. I have seen this type of failure on optics before in optical instruments when we have applied accoustic shock waves to them.

Fortunately the reflector is metal - if this had been a S4 you would probably also need a new reflector.

This can happen with any halogen lamp - the manufacturers include a caution on the lamp failure in every box. A FEL, GLC, GLA, HPL and any other halogen lamp can all produce a failure like this - fortunately it is very rare. All the halogen lamps contain a gas at a similar pressure - if they don't they don't work because the halogen cycle controls this. The variables include the filament temperature, filament size, quartz envelope size

Replace the lenses and the lamp and return to service.

I recently cracked a lens in a colortran zoom using an FEL. Brought the fixture indoors after it had sat for a few days in my van at -20 degrees centigrade, clamped to a pipe and after 30 minutes turned it on and heard the crack after only five minutes of operation. Differential rates of expansion of materials cause real problems when fixtures are cold like the one I had. Normal room temperatures are not normally a problem. But the failure was caused by my not allowing enough time for the fixture to reach room temperature before turning it on - not that the FEL the fixture or the lens was faulty.

#### icewolf08

##### CBMod
CB Mods
The FEL ain't rated for most fixtures and even if rated for it, your's ain't efficient in using them as opposed to other lamps more recent to the market. It's a selling point for more efficient lamps budgeted for next year.

Go with it in selling it even if not normal to be a problem. In the end... Killroy Visited You as it were. It's rare and spectacular ain't it.

Get rid of them FEL's for other reasons than this filament spectacular escape.
As I mentioned, it is probably a fluke that this unit still had an FEL in it. I have only stocked HX-755s for these fixtures for the past two seasons (mostly thanks to your recommendations). However, I would take this to management with the pitch that the fixture is at fault to see if they would give me the money to replace the last 45 in my inventory.

And yes, other than this being very cool and kinda pretty, it was certainly a great example to use as education for my crew. I have seen some pretty spectacular lamp failures, but most of my crew had never seen something like that. Par of my wants to fill the lens with epoxy and keep it as art (and an educational piece).

This can happen with any halogen lamp - the manufacturers include a caution on the lamp failure in every box. A FEL, GLC, GLA, HPL and any other halogen lamp can all produce a failure like this - fortunately it is very rare. All the halogen lamps contain a gas at a similar pressure - if they don't they don't work because the halogen cycle controls this. The variables include the filament temperature, filament size, quartz envelope size

Replace the lenses and the lamp and return to service.
I am aware that this can happen to any lamp, I have seen HPLs go out in some pretty spectacular ways. It is fortunate that it is rare, it just seems less rare in FELs. As for replacing the lens and returning to service, that is easier said than done on account of I have no more 6x9 lenses. It isn't worth me buying a lens for these fixtures as I am already planing to retire and replace 4 of them. I do have 6x12 lenses for them, so this unit will live to see another day. If this had happened to a source four, I would have a new lens here tomorrow, these fixtures just aren't worth much more than the time it takes us to service them each year.

Last edited:

#### JD

##### Well-Known Member
What I remember with those FELs is that the filament would sag until it was close to the quartz, which would start to bubble out. Use to see the same thing in some par bulbs that didn't use center supports. I used a lot of VNSPs where it is very visible because of the clear front. I can remember rotating lamps whenever I saw any sag starting. Can't be sure it ever extended any life and I never really kept track.

#### lieperjp

##### Well-Known Member
Do it. This would be a cool thing to keep around, especially if you make the fixture a part of that art/educational piece.
Make it into a table lamp! Erm... maybe not.

#### derekleffew

##### Resident Curmudgeon
Senior Team
Alex, you need to post your lens picture here.

#### church

##### Active Member
When I was preping some fixtures to go out on rental I found a HPL 750 about to self destruct lloked very much like Derek's above but with a bubble in the side of the quartz envelope. The lamp was still working but I removed it and stuck it in the garbage before it destroyed a lens or reflector. As I pulled it out the envelope seperated from the base. This was a new lamp with less than 10 hours on it. When I checked the lampholder I found one of the contacts was also burned to a crisp.

#### thatactorguy

##### Active Member
Alex, why does there appear to be about a 1/8" hole in the lens tube's right colorframe clip?
My guess is that the hole was for a self-threading screw or some sort of pin or clip to help hold the gelframe in place if the instrument were hung in such a manner that there was a chance of the frame coming out. Just a thought...