Fresnel Lenses

Hmmm - my initial thought would be that the lenses are rated for the heat but would probably have an upper limit or threshold.

I would also imagine that this would be fairly higher than the expected heat transfer from the lamp.

However, impurities in the glass or the tempering process could cause a problem as could any physical damage (chips, cracks).

Over heating through poor ventilation or the lamp being positioned close to the lens for a lengthy period of time would certainly cause a heat build up but I wonder if it would be significant to cause it to break.

Was the fixture dropped whilst hot?

I am simply guessing here but given that the lens is designed for these fixtures and I have never seen one fail, I would imagine that there may have been some physical damage, especially since you say the lenes fell into pieces.
I have had one shatter one time while only the other tech and i were on the stage(thanfully). This specific lens was chipped a little on the edge. We think this caused it to shatter into about 5 pieces.
Sometimes Fresnel lenses will normally spider-crack (small lines that radiate outward) over time, from heat and if foreign matter gets onto or into the lense (like mylar or confetti...oils or when dry graphite lubricating powder does not get cleaned out it can burn in small pock marks that over time can weaken a lense), so occasionally they can split or simply break over time.. Usually they do not fall out of the air--most fresnels have a cage over the front. If the lense is subjected to impact while hot it can also cause or add to this breakage problem happeneing. Another contributing possibility is if water or moisture gets on the lense while hot...and also if you take a lense that has been exposed to extreme cold and you put the fixture on full--the suddent extreme temperature change can contribute to cracking.
If its a new fixture and the lense breaks, its usually a lense that wasn't properly made or tempered...I know Strand has had a few of these lense problems in some of their new Fresnels and they are aware of it and have dilligently replaced them at no charge.. We had 6 or 7 of our new 10" lenses crack in half on the first use after we got a new stock of Fresnels in..and Strand took care of it quick.

The fresnel was old to begin with, it is one of the originals from the school. They won't buy us new lighting equipment at all. It has been hanging all alone on one bar since the beginning of March and it has been barely used. I do periodic checks of the lights and I checked all the backstage ones an hour before it happened. This included this fresnel. Everything was normal, no cracks in any lenses, all the lights worked perfectly. We just heard a small noise and then the lights flickered and the lens dropped out in pieces. So it did break in the light and then fall. Everything on the light is still intact. Includeing all the metal pieces that hold the lenses in place. I have never seen this happen before, I just want to find out what caused it.

The group that this happened to was a symphony, does that make any difference?
Were they playing THAT bad? :) looking into info for my "science show" (there's another thread on it arround here) I have found that you can shatter glass items such as beakers buy shooting enough of the exact right frequency sound at them. Several catches are the fact that the glass has to be a on a surface that does not hinder its vibration (unlike being clipped into a fresnel). I have some serious doubts that the cause goes back to sonic roots.
If it was sonic roots, than the lens would have broke during our musical in March, or during on of our band concerts. I think it had something to do with the heat, but the there was only a 500W lamp in the 750W fresnel so there was no way it could heat up enough to do anything.
I've had Altman 6" lenses on their 1K6AF units crack in half.

The lens came with the unit, which is a 1000 watt rated unit. I was using 1000w BTR's.

Altman informed me that I needed to install Fibertek insulators between the lense and the retaining clip, they sent me the insulators for free, but did not replace the lenses and declined to pay for the labor.

Last Altman fresnels I buy.

Over time I have seen a few cracked lenses in old lamps. It can be caused by a minor defect in the lens. But if you think about it the wear on a lens over time through expansion and contraction would put a lot of strain on the lens. A lot of the lights you can buy down here have some of protection in case the lenses shatters.
Peter said:
I have found that you can shatter glass items such as beakers buy shooting enough of the exact right frequency sound at them.

I believe this is coming on MythBusters pretty soon.
I have some Altman 165Q 6" fresnels that are about 10 years old in my theatre and many of them have 'spider-cracked' lenses. Except not only are they cracked, they're in peices. What we don't understand is that they are rated at 1kw and we used them at 750, and not even very often. (Our theatre is a semithrust so we use more side and front light than top light).
Our theatre is a procenium (sp?) thrust, so we use front lights only. Most of our stuff is done infront of the procenium so we just close the main reds and use the front lights. Our backstage lights only get used with concerts and the main spring production. Other than that, they are barely used so I can't seem to figure out what caused the lens to break. It wasn't even on for 10 minutes. and for concerts we usually run them 3 hours straight, but this light hasn't been used for that yet.
Falcon as you say the light is old. You may not use it much at the moment but you don't know the history of use for it before you were there. Even steel and iron over time can fail with constant expansion contraction or bending forces applied. Past use may have stressed it to the point of failure and the last heating up may have been to much. I think we have all taken a piece of metal or solid wire and bent it constantly until it breaks.
“The fresnel was old to begin with, it is one of the originals from the school. They won't buy us new lighting equipment at all.” - falcon

The Fresnel fixture has not changed much over the years so upgrades to it is often not cost effective in any real sense.

Wolf & Mayhem - Outstanding info

falcon - was it the lamp that exploded that caused the lens to break away or the lens itself with lamp intact? What model and brand of luminarie? (Answered as a Altman 165Q) What specific lamp were you using (?BTN) and given it’s fixture maintenance, who was the last one to clean the lens - and most importantly, with what?

“Small noise, and then the lights flickered” - that’s telling but without reference point, did the filament break in now becoming an arc lamp that caused explosion, and if so since a normal Fresnel lens is designed to be sufficient to hold in this explosion, what was the defect in the lens or it’s care and using a fixture with a cracked lens before this breakage that caused the lens to subsiquentially break? Two different things here, first the described explosion, and given this, the breaking of the lens.

“165Q’s” The focus rail type, now there is something I learned about just this weekend. Didn't think they made any of this type.

I might think that the cracked lenses are in part due to some residue left on the lens from say bad ideas on how to clean them. Hard to say as to the cause of the lens cracking, could have been many issues including bad lenses etc. That’s a direct to Altman question in furnishing data with what lot number the lenses were. They might replace them due to past problems with that lot of lenses, probably will not. Can be many issues that cause a lens to crack including cold/wet lenses etc.

In my tiime on the stage, I’m yet to have a Fresnel lens crack (not chip and still work) so I can’t say.

Don't know what caused your lens to crack and later break as expected, perhaps in some only worth while concept to watching CSI-what ever, you than learn the trade in analizing all info as to what caused it to happen and how to prevent it. Investigate all similar fixtures, try to re-produce the results etc. in finding the real answer. Until than, speculation is speculation as to what each of us have seen. Might or might not be the cause specific to your case. Follow the scientific theory.

“I've had Altman 6" lenses on their 1K6AF units crack in half.

The lens came with the unit, which is a 1000 watt rated unit. I was using 1000w BTR's.

Altman informed me that I needed to install Fibertek insulators between the lense and the retaining clip, they sent me the insulators for free, but did not replace the lenses and declined to pay for the labor.

Last Altman fresnels I buy.” - SteveB

I normally replace or install various fiber insulators between lens and clip. Such insulators don't last for ever and need replacement with probably each time you remove the lens. Just part of doing a high temperature fixture and retaining it's lens. Lenses at high temperature with failed insulators would tend to fail in use otherwise. Just something about lenses and how they are retained I expect.

I hope this due to labor reimbersement or an upgrade would not send you away from one line of fixture over another.

This would be a shame. Altman sending the upgrade for free as opposed to me paying $100.00 each for a different Studio Fresnel upgrade kit that was heavily discounted in dealer cost is a excellent price.

If the cause of the lenses breaking - in something I have not seen with my own 1K6AF fixture is because of how the lens is retained, they than would not need to replace the lens given it’s upgrade to mounting. Much less, now let’s speak brass tacks here, would you really just throw out the now extra lenses?

As for labor in installing the free upgrade... , I might say some, but in the end it’s not the policy of any company to pay you the labor for the upgrade to the fixture that was the best attempt at the time for them and found to be in need of re-design.

How many people than could charge for upgraded lamp bases and reflectors to the 360Q series of fixture that was designed as good as it could be for it's day?

Sorry but it’s not a new car. Read your manual/contract. With us it’s a constant battle as the only (at some point) official Martin repair shop to get labor for upgrades reimbursed, and it’s limited specific reimbursement at that, given very specific paperwork filed.

This given one of two besides them authorized service shops. Are you a authorized Altman Service Center? Only those companies recognized by the dealer/service center can make upgrades to the gear if such a thing is taken to specifics of paying for labor. They might pay for my labor as more pain in their rear than worth it, but I am a pain in their rear on a monthly basis anyway and am the test market for the upgrade kits. I don’t charge for labor in an upgrade, it’s part of the development of the fixture. On the other hand, were I to charge for my labor it might at some point be more a payoff of dispute than reality in a actual paying for labor type of way. They don't pay for labor, it's really rare anyone will. Get over it and concentrate on the fixture.

My 1K Fresnel fixture don't stay in focus, that's a design flaw. That's a deciding factor in not buying more not arguing about labor when parts are provided.

Should you wish you can privately sue the engineer that developed the gear Altman, and UL to re-coop your losses in labor as a separate issue but it will probably be thrown out of court. Such gear upgrades is a safety thing and they were as normal at best doing right by you in providing the repair parts for free.

I have the only attempt by them at a #5000L upgrade kit for resale on a shelf at the shop. This after a very long and + $6K smaller wattage Fresnel upgrade kit for other fixtures. It did not work with all fixtures in standardized mounting holes, and in general had problems.

Instead, we paid shipping one way, and they paid the other way to upgrade the other 5000L fixtures in our inventory to the second upgrade to the fixture directly at the factory in doing so. Upgrades come from the factory or authorized service centers if you wish for them, or in providing you the parts allow you to save money on the factory upgrade.

As a semi-authorized service center, I might have been able to charge them with my labor for your fixtures, but still will have had you as also normal pay for shipping, it's not the local Ford Dealer. Sorry, but that’s just the way it is in servicing upgrades. You won’t find any better in a free upgrade however no matter the brand. Nobody would pay my as per Union Lead Electrician’s salary to upgrade their gear as opposed to that of a high school kid’s salary in upgrading the same gear. Get the point here in part in why they don’t pay for your labor to gear bought “as is” and functioning well to the best of their design and UL listing in testing?

Sorry but I fear you are on the wrong track with this Altman dispute. They did the best they could in sending parts for free as not otherwise normal to the end user. Given this, and it is gear bought "as is" up to the design tecnology and UL Listing testing of the equipment of the time safe to use. Altman's a compan, and while I might not buy more 1K Fresnel fixtures due to a smaller beam spread, upgrades to it is more benefit to me in having a money saving solution that saves money on repair parts than worrying about who pays for it. I assure you that nobody pays you to upgrade the gear you buy unless you go thru legal or dealer/authorized service center loops.

Heck, Inkie can attest to my having to go up to the top of 55 story buildings at times to fix or replace or upgrade even architectural lighting fixtures that don't live up to warranty. Parts are provided once you fight for them, but labor is assumed. Same as that 1 in 90 lamps that fails before it's rated hours. Can you charge the company both for its "expected life" and for labor in changing, or if almost that expect any compensation?
The lamp was still intact and still burning brightly after the lens broke and fell. I had last cleaned it with alcohol wipes, and removed any oils on it that way before i put it up back in march. I believe the fresnel is by Electro Controls. It maches our dimmers and patch panel. All of our lights except for 4 are made by them. I believe the lamp in there was either a BTR or BTN, whichever is the more poplular for fresnels. When we ordered them we just told the company they were Electro Control fresnels so whatever they gave us is in there. The fixture itself isn't damaged at all, the only thing different with it now is that it has no lens. Everything else is still intact.
Did you notice anything interesting or unusual about the broken bits of the lens? I would imaging that it broke into several large sections rather than shattering into hundreds?
there was the one larger section that was a little more than half the lens and there were two other considerable smaller pieces and everything else was just shattered glass. I'm thinking it fel in 3 pieces and when it hit the ground the two broke some more and the larger piece actually fell into a drum.
Was there any darkened or blackened areas or other markings on it?
So what actually caused the lights to 'flicker'? It doesn't sound right that they flickered and still worked after the incident. Usually the broken lens will not effect the electrics.
I wonder if the lens cracking caused enough of a vibration to cause the filament of the lamp to also vibrate resulting in a flicker but not enough to cause it to fail. Or perhaps it was sufficient to identify a wiring fault (bad connection or loose connection) that had not otherwise occurred.
I didn't see any blackened areas of the lens. So if the cracking caused enough vibration to make the light flicker, than how did it crack in the first place? Once I know how it can crack in the fixture like that excluding the possiblity of too much heat, which I can safely say there wasn't due to the lower wattage lamp. Its weird that the fixture itself isn't damaged at all. It is the same, except now there is no lens.

Users who are viewing this thread