T8 Lamp Glass Breakage

[ZCBee]

I have noticed in our facility that we have a small percentage of F32T8 lamps breaking their glass envelope at one end near the filament. I believe it starts out as a small break similar to a windshield crack caused by a flying pebble. This then grows around the circumference sometimes causing the lamp to fall out of the fixture and crash to the floor.

The filament ends have non-uniform blackening and my guess is that near the end of life, the filament is somehow cracking the glass. Is anyone aware of this issue and possible causes and remedies? These luminaries are on 5 days a week for most of the year. Some luminaries are on 24/7 (emergency lighting). I have never seen this type of failure with T12 lamps and am speculating that the filament's closeness to the glass envelope is contributing to the breakage.

 

[jeremysterling]

I have noticed in our facility that we have a small percentage of F32T8 lamps breaking their glass envelope at one end near the filament. I believe it starts out as a small break similar to a windshield crack caused by a flying pebble. This then grows around the circumference sometimes causing the lamp to fall out of the fixture and crash to the floor.

The filament ends have non-uniform blackening and my guess is that near the end of life, the filament is somehow cracking the glass. Is anyone aware of this issue and possible causes and remedies? These luminaries are on 5 days a week for most of the year. Some luminaries are on 24/7 (emergency lighting). I have never seen this type of failure with T12 lamps and am speculating that the filament's closeness to the glass envelope is contributing to the breakage.

I have seen the lamp failure you speak of. It may be a result of using instant start ballast, but you should consult the ballast manufacturer to confirm.

You might:

1. install wraps, cages or lenses (to prevent broken lamps from falling)

2. periodic mandatory relamping.

 

[mnbiker]

i have found some here too. most have a pin hole or crack near the filliment, we were able to return for credit. all on the t-8's, the t-5 and t-5 HO no problems.

 

[sameguy]

Relamping should be at about 80% of rated lamp life.

 

[al hildenbrand]

I have noticed in our facility that we have a small percentage of F32T8 lamps breaking their glass envelope at one end near the filament. . . The filament ends have non-uniform blackening . . . These luminaries are on 5 days a week for most of the year. Some luminaries are on 24/7 (emergency lighting). . .

Interesting observation. I have not seen this yet. Do you recall, are the lamps made by various manufacturers, or are they all one brand?

 

[ZCBee]

Interesting observation. I have not seen this yet. Do you recall, are the lamps made by various manufacturers, or are they all one brand?

This happens on one brand. I do not recall the previously used brand having this issue.

My theory from the observations is this: The lamp is near the end of its life. The filament heats, breaks and snaps against the tube causing a jagged pinhole break, like the windshield and pebble example. Now, not sure why the glass will break around the circumference after this event. The reason I mention this is because there are more lamps with the pinhole break but not all develop the circumferential break. But, all have signs of the little pinhole.



Am I allowed to mention the two brands here?

 

[hurk27]

I would say that if that is what is happening the lamp would no longer light even a very small crack would release the vacuum on the lamp and cause it to stop functioning, and for sure a pin hole would.

So are these lamps that have been out but left in place and they just finally fall?

 

[ZCBee]

I would say that if that is what is happening the lamp would no longer light even a very small crack would release the vacuum on the lamp and cause it to stop functioning, and for sure a pin hole would.

So are these lamps that have been out but left in place and they just finally fall?

I agree 100% and only add that the glass is weakened near the filament. Some do not develop the break around the circumference. Some do not get the pinhole break. We use an F32T8 Instant Start, "Intelligent Voltage" (120 to 277) ballast. We have not tracked replacement dates but I do not believe we our getting full life out of this brand of lamps.

We change burned-out lamps soon after identified, usually a week or less, but sometimes longer. Some break while twisting, some have the pinhole, a few have fallen before we replace. We are noticing many with at least the pinhole break but not all. We are too busy to track this by date of change, etc.

I am calling the manufacturer to inquire and will post if I learn something new. Thanks for the replies.

 

[Cow]

If it's a safety issue, I'd recommend tubeguards.

 

[stevebea]

I have noticed in our facility that we have a small percentage of F32T8 lamps breaking their glass envelope at one end near the filament. I believe it starts out as a small break similar to a windshield crack caused by a flying pebble. This then grows around the circumference sometimes causing the lamp to fall out of the fixture and crash to the floor.

The filament ends have non-uniform blackening and my guess is that near the end of life, the filament is somehow cracking the glass. Is anyone aware of this issue and possible causes and remedies? These luminaries are on 5 days a week for most of the year. Some luminaries are on 24/7 (emergency lighting). I have never seen this type of failure with T12 lamps and am speculating that the filament's closeness to the glass envelope is contributing to the breakage.

Typically this is more of a problem in T5 lamps close to end of life. At 5/8" diameter on the T5 the cathode is in very close proximity to the glass envelope.

 

[stevebea]

I would say that if that is what is happening the lamp would no longer light even a very small crack would release the vacuum on the lamp and cause it to stop functioning, and for sure a pin hole would.

So are these lamps that have been out but left in place and they just finally fall?

I agree... when you lose vacuum you lose ignition but the ballast will still try to ignite the lamp unless the ballast has end of life stop sensing.

 

[stevebea]

This happens on one brand. I do not recall the previously used brand having this issue.

My theory from the observations is this: The lamp is near the end of its life. The filament heats, breaks and snaps against the tube causing a jagged pinhole break, like the windshield and pebble example. Now, not sure why the glass will break around the circumference after this event. The reason I mention this is because there are more lamps with the pinhole break but not all develop the circumferential break. But, all have signs of the little pinhole.

View attachment 5923

Am I allowed to mention the two brands here?

When the electrode breaks the wire drops and touches the lamp which explains the pinhole. I would assume if the ballast does not have end of life protection and keeps trying to ignite the lamp eventually the high temp. of trying to start would lead to the break.