Lamp Questions

[StillLearning]

I guess I am still being too brief to be clear. We have an auditorium which is used for a lot of purposes besides performances. They use one or two presets for non-performance time, and the lights are set to that preset most of the day (12-16 hours) almost every school day. Some of the lights that are recieving around 60-70% of their rated voltage are blowing out in only a few thousand hours. As pointed out, they should be lasting in excess of 370% life, or 7000 hours.

I talked to Ushio and they told me about their 90% rule and appoligized that their calculator does not take halogen cycle into account.

All of your thoughts in your first paragraph about dimmers, profiles and hot to cold or vice versa are good points, showing that I need to clarify my question..

Clarification - I am talking about long term (several hours or more) operation at a measured % of rated bulb voltage on a typical stage (30 degreesC) in a Source Four PARnel or Zoom pointed about 45 degrees down.

The practicality of knowing is being able to go more than a few months between bulb changes.

[shiben]

To be honest with you, it seems that unless you really need incandescents in there for some reason (like being able to dim them), you might check out the Source 4 HID version? Its rated for 12,000 hours. I feel like your not going to get very long lasting lamps unless you use a discharge lamp of some sort. At our basketball arena, we have Source 4s with the long life halogen lamps in them, but still not HIDs, and its a pain to replace them no matter how often you need to do it, be it once a month or once a year. How many of these guys do you have, and do they need to be dimmed, or is that for

[icewolf08]

Originally Posted by StillLearning

I guess I am still being too brief to be clear. We have an auditorium which is used for a lot of purposes besides performances. They use one or two presets for non-performance time, and the lights are set to that preset most of the day (12-16 hours) almost every school day. Some of the lights that are recieving around 60-70% of their rated voltage are blowing out in only a few thousand hours. As pointed out, they should be lasting in excess of 370% life, or 7000 hours.

I talked to Ushio and they told me about their 90% rule and appoligized that their calculator does not take halogen cycle into account.

All of your thoughts in your first paragraph about dimmers, profiles and hot to cold or vice versa are good points, showing that I need to clarify my question..

Clarification - I am talking about long term (several hours or more) operation at a measured % of rated bulb voltage on a typical stage (30 degreesC) in a Source Four PARnel or Zoom pointed about 45 degrees down.

The practicality of knowing is being able to go more than a few months between bulb changes.

Here is the real thing. If your fixtures are going to be on for 12-16 hours a day, you should see lamps fail on average around the rated life of the lamp. If you get "a few thousand" hours on a 2000 hour lamp then you are in good shape. That would mean that you are only replacing lamps about every 180 days, which doesn't seem so bad. Consider that the rated life of the lamp is based on the average life of some large sample group. Some lamps may last significantly longer while others may fail prematurely. It is an average, not an exact science.

Now, as was mentioned, if the "non-performance" usage of the fixtures is basically for worklight or rehearsal light, just to have light on stage, then you should probably look into some CDM or Metal-Halide fixtures. These fixtures, while bearing a larger up-front cost and higher cost for lamps are more economical over time as the lamp life is excellent and they are much more efficient in terms of lumens per watt. The only real downside is that most CDM and M-H fixtures take some time to warm up to full intensity. However they are a much better match up for a 12-16 hour/day burn time. One of the other great advantages of using CDM fixtures is that they don't need dimmers. Put them on plain old non-dimmed, switched circuits and then you have freed up the dimmers that you were using for worklight!

At my theatre, I do use source four PARs as work lights, and most days they run at full for an average of about 10 hours a day. I expect to have to replace the lamps in them about once a season. We debated going to CDM fixtures when we were looking for new work lights 2 ears ago, but decided to stick to standard fixtures due to the fact that we need the instant on capability of T/H lamps.

So, I would weigh the cost of your options vs what you need to accomplish. Look at whether or not you have more lights on in your presets than you really need. Cutting lights out of the presets will save lots of lamps. Ultimately though, it sounds like you are getting exactly what you should get in terms of performance from the lamps you are using.

[StillLearning]

Thanks, Maybe time for more clarity. This is for a High School (read that, "No money unless you have a great reason and can wait a few years"). I am just trying to make the best of a bad situation.

My plan is to convince the school to install some flourescents /HIDs in addition to the HPLs, so we are only using halogen for performances. However, I need a number for the lower limit of the halogen cycle so I can put it into my model for bulb life and operating costs.

I'm fairly sure the 90% of rated voltage number from Ushio is much higher than reality, some history indicates that 50% of voltage seems to be below halogen cycle temperatures, but I'd like a better number if anyone has one. If not, I'm going to try some measurements with themocouples and IR thermometers, but I thought it would be easier to ask first.

[StillLearning]

Originally Posted by icewolf08

Here is the real thing. If your fixtures are going to be on for 12-16 hours a day, you should see lamps fail on average around the rated life of the lamp. If you get "a few thousand" hours on a 2000 hour lamp then you are in good shape. That would mean that you are only replacing lamps about every 180 days, which doesn't seem so bad. Consider that the rated life of the lamp is based on the average life of some large sample group. Some lamps may last significantly longer while others may fail prematurely. It is an average, not an exact science.

Thanks for your thoughts. I understand averages and curves, but at 90% of voltage or less these lights should be lasting over 7000 hours. We are getting nowhere near that. I'm trying to find the reason. Many of the bulbs are in a position where we need to rent a lift to change them. Real pain, no forethought in construction.

I can review almost everything else, but if I knew how low (85%, 80%, 75%, etc. ) I can run the bulbs before I started reducing their lifetime I could set all the presets to not let that happen.

[shiben]

The fact of the matter is, the lamps are rated for 2000 hours, and thats kind of where they will fall. I highly doubt your going to ever see 7000 hours out of a HPL, except in some flukey circumstance. Basically, when you run a lamp like that for a long time, it will begin to fail, and then go out. Its a pain to rent the lift, but its kind of going to be the reality unless you get some different equipment in there. Even if you do get right on the edge of the halogen cycle, your still going to see lamp failures fairly regularly. I hate to say it, but I highly doubt there really is anything that you can do about the situation, other than try and convince your bosses that some form of alternative lamps is a good buy. I totally feel your pain, if not worse, as in our arena for aisle lighting they went for the higher output HPLs, and they need replacement every 300 hours. Some of those are underneath the catwalks, and you need to strap in and climb out onto a beam to get at them, or rent an 80 foot boom lift (which there is only one of in West Michigan, but its not available for rental, so you need to go to Chicago to get one). Fact is, lamps die, and part of your regular maintenance schedule is going to have to be replacing them. No one likes doing it, and its often a pain in the rear, but it comes with using high-wattage lamps. Realistically, there is nothing you can do to make those lights extend to 7000 hours.

[ship]

First do not consider halogen cycle not working at X percentage of dimmer on +/- 120v line voltage circuits. Those notes of the halogen cycle effect on halogen lamps where the free halogen gas components attack the cooler parts of the lamp in causing premature failure are for low voltage lamps = under 68v lamps as a concept. This and for low voltage lamps it would seem in other than series condition such as a MR-16 cyc light might see where it's 120v but distributed in series instead of an individual lamp dimmed. (Don't know why but it is the case.) Ask Usho's Dr. Bulb about that concept.

In general at 120v +/-, that voltage is sufficient at any dimmer intensity to make the halogen gas preform properly no matter the intensity from what I'm told in asking manufacturers about this specific issue many years ago. You have a very valid question but it's not the cause of your problems.

To be more specific, how much by way of bubbles in the pinch/globe area do you see in etching and melting away of the glass where the filament comes into the globe of your failed lamps and how many times do you have blow outs there or at the fill pinch? Those are the coolest parts of the lamp and where the free chemicals in the halogen gas attack when board. I would assume other than filament failure, pinch failure is going to be really really rare in your situation which confirms end of life being the cause and not free under voltage halogen gasses killing off your lamps. Remember, each lamp's failure has a cause, study what caused that lamp to fail and you know of a potential problem. Doubt you have many or any monofoil pinch or fill pinch failures in HPL lamps.

Hit up the Sylvania website, do a search for the HPL lamp and cick on one of them. Hit the "Doccuments" section and print up and read the ... forget what it's called but it's about low voltage lamp design in PDF form. All kinds of info about halogen lamp design and details written in a way that if you are ready to learn it's easily understandable. Good PDF for free book. If Usho still has the articles from Dr. Bulb, also good info provided.

Assuming that the effects of dimming your lamps is not playing a role on why your lamps are not living up to your expected lamp life for the lamps we need to look into other things.

-First the voltage at the fixture and that verses the voltage of the lamp used.
-High output or long life HPL lamp, 120v or 115v?
-What's your dimmer trim setting and type of dimmer and control in use at all positions the lights are controlled from?
-You mention other than show uses are at x percentage, how is that done to assure it's not just saying "oh' yes, we only bring it up to 70%?"

Beyond this we get into details about the care for the fixtures. Put a fresh lamp into a bad lamp base it's gonna go bad really soon. Same with cooling and cleaning of the fixture. Not to assume anything but there can be lots of reasons for a lamp including and especially one finger touched or one in a high dust or dirt or fogged environment to go bad before its time. What do the lamps look like in going bad before their expected time?

So at least as a start there are a few things to figure out and check for now in troubleshooting what is causing this problem. Refinement of the above will hopefully solve the problems in such lamps should last in theory at least the expected lamp life time.

[StillLearning]

Thanks Ship, great references.