Conventional Fixtures When to Replace Lamps

Harrison

Member
Silly question - but I'm curious.

When do you guys replace the lamps in your conventional fixtures? Do you want till it blows? Do you try to predict how many hours are on it and replace it before it would blow? Is there a way to tell when it's nearing end of life?

Thanks
 

SteveB

Well-Known Member
When it fails.

If it's a smart design, no one lamp should be critical, doubled up specials, etc... I know, I know, not always possible or practical, but helps alleviate blow outs being noticed.
 

seanandkate

Well-Known Member
Fight Leukemia
I'm with Steve. You can't reliably predict when a lamp will fail, so I wait until it goes nova, or fails completely.
 

JD

Well-Known Member
In theory, when a lamp blows, the flashover could take out the dimmer channel. In practice, my heyday in lighting was 1978 to about 1998. Hundreds, if not a thousand lamp failures in an uncountable amount of shows over the years, never took out a dimmer. Lamp failures can happen at any time, and due to the nature of duty-cycles, they all age differently so I would agree, wait until they blow.
The exception to that is if you notice a blistered out lamp. In that case, change it so it doesn't damage the fixture or rain hot bits down on those below.
 

Les

Well-Known Member
+ 1 for waiting for it to fail. Keep in mind that while lamps have an estimated lifespan, there can be a really wide margin. I believe the way they are tested is to burn the lamps in relatively large batches, and when 50% have burned out, call that the average life (or round to the nearest whatever). With manufacturing being what it is, I'm sure they will all be reasonably close. But in addition, your particular venue's electrical service (or dimmer's trim settings) could have an effect on this. My venue gets 127v. Yours could get 119v. This will have some effect. To confuse matters more, avg lamp life does not necessarily account for how long your fixtures may spend at ~90% rather than FL, which measurably increases lifespan. On the contrary, if you want a little more light reading, study up on the Halogen Cycle. Running continuously below a certain % threshold can have an adverse effect on usable lamp life, in that the envelope will become clouded with deposited tungsten and really kill your intensity. Obviously, there is a bit of a balance in getting the most out of your lamps, and knowing what is going on in the back-end of things.

Overall, it's just too hard to pinpoint when a lamp will fail, and replacing proactively without potentially/probably wasting a bunch of money. Then we get in to power fluctuations, HVAC vibrations, thermal shock, etc...

Now, is there a way to tell when they're about to go? If the glass is bubbled (as mentioned above) or if the filament is sagging close to the glass (I've heard of some people flipping the lamps if this is the case - YMMV), it is a good idea to just drop a new lamp in. I haven't ever noticed any difference in intensity between a new lamp and an old one. Especially not to the point where it would require a replacement. Wiping the dust off the gel would likely have a larger effect.

** Now if you see that the lamp pins are scorching/pitting, replace the lamp and socket right away.
 
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sk8rsdad

Well-Known Member
Premium Member
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On the other hand, in some places getting access to the fixtures is a problem. For instance, most schools in my area don't have the equipment to reach their FOH positions in their gymnatorium/cafetorium/who-thought-this-was-a-good-idea-atorium. In those places, if you lose one lamp then it's best to replace all of them at the same time.
 

JD

Well-Known Member
(I've heard of some people flipping the lamps if this is the case - YMMV)
Guilty! Used a ton of VNSP PAR64s back in the 80s and if I noticed sag, I would spin the sucker 180. Hard to say if it had any effect as the "longer" filament would probably just sag in the other direction, but did it anyhow! Besides, the VNSPs were very visual in that you just look in the front of the can and you don't need to disassemble or unplug anything to "spin the bottle."
 

AudJ

Well-Known Member
Well in my school auditorium, we wait until a lamp goes, then go to the box of a dozen spares I purchased to find it empty because another building needed them. Then I submit another requisition for 12 light bulbs (yes I know they are lamps, but if I request lamps, the purchasing agent brings in all the table lamps in basement storage and tell me to pick from them to save money). Then the purchasing agent assumes they are LED light bulbs due to the cost, and won't approve them because I just bought a dozen a couple months ago. After explaining, they research replacement LED light bulbs that they believe will work, but of course they will not, so they bid my request out to 3 different vendors, none of which can beat the price I submitted originally. Finally the Purchase Order is generated, waits to be approved by 3 administrators and submitted to fill the order. The Lamps arrive 3 days later, and I install one, and place the remainder in storage for another building...

So to answer the original question, I replace lamps about 6-8 weeks after they fail.
 

JD

Well-Known Member
Well in my school auditorium, we wait until a lamp goes, then go to the box of a dozen spares I purchased to find it empty because another building needed them. Then I submit another requisition for 12 light bulbs (yes I know they are lamps, but if I request lamps, the purchasing agent brings in all the table lamps in basement storage and tell me to pick from them to save money). Then the purchasing agent assumes they are LED light bulbs due to the cost, and won't approve them because I just bought a dozen a couple months ago. After explaining, they research replacement LED light bulbs that they believe will work, but of course they will not, so they bid my request out to 3 different vendors, none of which can beat the price I submitted originally. Finally the Purchase Order is generated, waits to be approved by 3 administrators and submitted to fill the order. The Lamps arrive 3 days later, and I install one, and place the remainder in storage for another building...

So to answer the original question, I replace lamps about 6-8 weeks after they fail.
Some things NEVER change! Way, way, WAY back when I was in High school, we had a series of instruments located in a cove. You could access them from a catwalk above the ceiling. That's where I hid the replacements lamps! Right under the catwalk, next to the fixtures.
 

RickR

Well-Known Member
@sk8rsdad has a good point. In the architectural world it's known as group relamping. Cost to set up for the work (scaffolding to 30' ceiling over seats?) and tolerance for failures are key factors in setting the time span.

Some TV studios have double fixture hangs and instant cross over circuiting because they need ultra-reliability. But some just relamp on schedule. Even with our "expensive" lamps it can be quite reasonable to throw away 80% used lamps.
 

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In college one of our alum went to go work for one of the Cirque touring shows. He was on a tent tour doing 6-8 week sit downs. At each stop they would re-lamp all the conventionals in the rig. So, every 6-8 weeks a large box of partially used lamps would show up to my college as he would save them from the dumpster. We would clean them and throw them in fixtures and it worked out great. They did it because getting to the places these fixtures hung was nearly impossible after the show was in... the cost was just another expendable.
 

variable

Member
My main fronts are all 750w HPLs with a 300 hour life, so I pull them about 3 times a year. Generally I'll wait until one or two blow to prompt me, then I'll do the whole pipe unless it's been less than 4 months since they were last replaced. The rest of my instruments I re-lamp when they blow.
 

gafftapegreenia

CBMod
CB Mods
We had a company come through about two and a half years ago and re-lamp all our high bay fluorescent fixtures in the scene shop. They spend over a week on the scissor lift swapping tubes and replacing broken units. I think we've only lost a tube or two since.
 

BillConnerFASTC

Well-Known Member
My main fronts are all 750w HPLs with a 300 hour life, so I pull them about 3 times a year. Generally I'll wait until one or two blow to prompt me, then I'll do the whole pipe unless it's been less than 4 months since they were last replaced. The rest of my instruments I re-lamp when they blow.
I assume they are not easily accessible so therefore group relamp.
 

Harrison

Member
Thanks for all your feedback. I (as most do with smaller budgets and less than ideal venues) live in a world where I never have the luxury of a backup or doubled fixture, but also never have the budget or can justify relamping before something blows.
 

kicknargel

Well-Known Member
I don't have imperial research, but I like to do pre-show dimmer check by snapping lights to full (rather than dimming them up) on the theory that it will encourage end-of-life lamps to fail at the check, rather than during a show. Anecdotally, I experience many pre-show failures and very rare in-show failures.
 

StradivariusBone

Custom Title
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On the other hand, in some places getting access to the fixtures is a problem. For instance, most schools in my area don't have the equipment to reach their FOH positions in their gymnatorium/cafetorium/who-thought-this-was-a-good-idea-atorium. In those places, if you lose one lamp then it's best to replace all of them at the same time.

Our house lights fit this category. Our district finally figured out they needed to buy a spider-like base for a set of scaffolding that could be assembled and moved around over the seating to accomplish this task. Prior to that they rented a boom lift (diesel powered) and removed all the orchestra seating. After realizing that the theatre stank of combustion and all of the studs for the seats were bent they elected to never do that again.

Funny anecdote related to this story- two of us got relamped within a month or so of each other. Virtually same design, so same lamps. The electricians decided to do a little experiment and bought lamps from China and from Mexico. I got the Mexican lamps. Within 2 months, about 60% of the Chinese lamps had failed and by the time the district got around to relamping he was using S4 pars from the light bridges as house lights. Not sure if there's a lesson there, but it was an interesting experiment.
 

RickR

Well-Known Member
Thanks for all your feedback. I (as most do with smaller budgets and less than ideal venues) live in a world where I never have the luxury of a backup or doubled fixture, but also never have the budget or can justify relamping before something blows.

Group relamping can actually save money! That's a key fact for the budget people. Keep in mind you don't throw away a $20 lamp when you replace early. The pro-rated value of the remaining life can be very small! But as in many issues, it's a negotiation to find the right balance for any particular situation.
 

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