bulbs keeps blowing

[mcinnes01]

hi I'm a beginner in the lighting world and have as small DMX rig consisting of 8 lights. Recently I have been experiencing a lot of bulbs blowing on a ridiculously short time. However rather than the filament blowing it has been the glass base of the bulbs. I've recently moved to the long life Philip's ELP 250watt bulbs, as I was recommended this may solve my problem, however am still experiencing bulbs going after only a few hours use. I also had this problem with considerably more expensive hti152 discharge bulbs, where after a few hours usage the glass had what looked liked burnt and slightly bubbled at the side of the bulb.

 

As I'm very new to lighting and really don't have a clue of what may be causing this but I'm sure the bulbs are supposed to have a life of 1000 hours rather than just a couple. Does anyone know what could be the cause and solution. I thought maybe the power supply and so a power conditioner or possibly a fault with my actual fixtures, however the problem has occurred on various fixtures not just 1.

 

 

If anyone can help it would be much appreciated.

 

 

Thanks,

 

 

Andy

[gingertom]

The marks you describe on the sides of the envelope sound just like grease marks from fingers. Idealy one should not touch the glass at all, but if this does happen then a quick wipe off with white spirit should remove the grease, and thus the potential for "hotspots" on the glass.

 

HTH

[tokm]

After reading the O/P's post, I think gingertom's on the right track.. Never seen this happen any other way apart from if someone has touched the lamp with fingers.

 

Do you just install the lamps with your fingers, or do you use the little cover thing that lamp is already fitted in, when inside the box?

 

They're there for a reason..

 

Bit off topic, sorry: I think one of the ideas behind the development of the lamp common in most DJ fixtures now, known as a 250w ELC lamp, was to eliminate this issue of people touching lamps (either when they know they shouldn't, or don't know) Its basically a normal halogen capsule lamp with a reflector in a sealed.. Similar in some ways to a PAR lamp.. Means people don't have to worry about touching the lamp capsule accidentally and makes it easier to install all round.

 

Tom

[JimWebber]

Hi!

 

What angle are you burning the lamps at? Lamp life can be drastically reduced if they are used at the wrong angle...

 

Again touching the glass envelope is a big no-no!

 

 

Jim

[mcinnes01]

I'm very careful when handling the bulbs only touching the envelope on the halogen bulbs and using a clean dry cloth when handling the discharge bulbs. As far as burn angle I have my lights set so the bulbs are facing down approx 15 degrees back from a horizontal position. E.g. as you would set your scanners set on a T-bar. Could changing the angle of my lights affect this?

 

With the halogen bulbs the problem is that the envelope is cracking at the base, I've been told that other people experienced this over summer with the osram bulbs due to heat stress and that the philips long lifes have a slightly thicker base and so last longer. However this problem is still occuring.

[gareth]

With the halogen bulbs the problem is that the envelope is cracking at the base

That's almost certainly because you're ...

touching the envelope on the halogen bulbs

 

As others have already said, you shouldn't touch the glass envelope of any theatrical lamp (apart from pars) with bare hands - the grease spots cause premature failure. If you do touch the envelope by accident, clean the finger marks off with some IPA or some other appropriate solvent.

[mcinnes01]

thanks for your help everyone, I'll take more care when handling the bulbs in future. Thanks again.

 

andy

[Chris Beesley]

With the ELC lamp its worth checking the condition of the lamp base - if the contacts inside are damaged or corroded they will not provide a good electrical connection and they can overheat causing the lamps to fail. This is a fault common to older light effects or effects that have been used in slightly damp conditions.

 

Also another common fault is units not being left to cool fully before being removed from their t-bars and packed away - lamps are always more delicate when hot ... even the long life versions!

 

HTH

[Crew.Steve]

As Mr Beesley mentions, it is worth checking the base connexions. The tension in the spring contacts is weakened by heat and, if you are experiencing overheating due to a slightly resistive connexion, this will set up a positive feedback situation where more and more heat is generated until something turns black and severs the current feed. THEN you know where the fault was! (probably)

[jayselway]

I had quite a few ELC's which all had to be returned, as the lamp base cracked, jolting the filament and thus making the lamp fail. They lasted about 3 hours in the fixture, before going with a nice little "ping". I have yet to hear back about any kind of re-imbursement for these.

 

Had one on the bench, in an Acrobat, and watched the thing. Didn't touch the lamp at all when inserting it, and sure enough, after about 3 hours, the base went, and took the filament with it.

 

I'm using the ELC/5H now - and not had any of the problems listed whatsoever.

 

Before you ask, I didn't watch it continuously, but recorded it, and watched it back!

[RODALCO]

Touching the lamps will most likely cause the above symptoms of the bulgeing glass.

The correct burning angle is important too especially for the longitudinal halogen lamps.

Vibration may also be a cause in shorting lamplife drastically.

Poor lamp contacts cause overheating at the lamp terminals.

 

How accurate is you supply voltage under load ?

Any overvoltage 5% or more will shorten lamplife rapidly.