HPL Lamp brightness over life of lamp

[bluemando]

I am aware that projector lamps get dimmer over the life of the lamp. I assume this is the same for HPL lamps. Is that right? If so, is there a chart that shows the effects of lamp brightness and color temp shifting over the lift of the lamp?

Thanks,

Tim G.

 

[derekleffew]

Unlike gaseous discharge sources, HPL s and all other tungsten-halogen lamps exhibit no discernible change in output or color temperature over the course of their life, until ultimate failure. (Super Nova excluded.) Older non-halogen stage/studio lamps would darken with use as the tungsten from the filament would migrate and be redeposited on the inside of the envelope, but the halogen cycle remedied that.

 

[JD]

Unlike gaseous discharge sources, HPL s and all other tungsten-halogen lamps exhibit no discernible change in output or color temperature over the course of their life, until ultimate failure. (Super Nova excluded.) Older non-halogen stage/studio lamps would darken with use as the tungsten from the filament would migrate and be redeposited on the inside of the envelope, but the halogen cycle remedied that.

Agreed with one exception. In some applications where the lamp is never sustained at a level where the cycle woks best (80%+) the depositing may start. Once started, it is a fatal trend as the deposit remains, dimming the lamp for the rest of its functional life, even it operated at full (100%) afterwards.

 

[derekleffew]

... Once started, it is a fatal trend as the deposit remains, dimming the lamp for the rest of its functional life, even it operated at full (100%) afterwards.

A representative of a major lamp manufacturer appears to disagree.

... As for the halogen cycle, I think the lamps need to run at full for the halogen cycle to work-- that said, it doesn't need to work ALL of the time. I always recommend doing a warm-up cue that at SOME point during the night brings the lamps to full for a minute. This allows the Halogen cycle to completely operate, and can "clean" the lamp. Then, if you are only running the lamp at 20% during the show, it's still fine as the halogen cycle at least gets to operate fully at some point each night. ...

 

[JD]

A representative of a major lamp manufacturer appears to disagree.

Cannot say I have ever seen one successfully "cleaned." I would love to see a demonstration of this, or a formal study. It simply gets to the point where even the envelope glows red when lamped off. Without the gas in the mix, the tungsten becomes a plating on the inside and can built to the point where the lamp is partly "silvered."

 

[chausman]

Unlike gaseous discharge sources, HPL s and all other tungsten-halogen lamps exhibit no discernible change in output or color temperature over the course of their life, until ultimate failure.

I, like JD, disagree that HPLs don't change over time. Why would a brand new lamp be brighter then the older lamps? Both bought at the same time, from the same manufacturer and dealer? These lamps are almost never run at full, only about 70%.

 

[Les]

They may marginally change, but not like arc lamps, which lose a good percentage of their output toward the end of their rated life. I also don't think a lamp such as the HPL changes color temperature in any dramatic way. As we can see, the useful lifespan of a TH lamp is modified by its environment and operating conditions, so no formal graph or chart (per the OP's request) would be useful as each particular situation varies, and no two lamps will be the same at their EOL.

I, like JD, disagree that HPLs don't change over time. Why would a brand new lamp be brighter then the older lamps? Both bought at the same time, from the same manufacturer and dealer? These lamps are almost never run at full, only about 70%.

Are the fixtures bench focused the exact same way, and both with perfectly clean optics? Upon examination, are there any noticeable differences between the new and used envelopes? I've seen a bit of translucent cloudiness before, but this generally appears near the tip of the lamp (which is not where the majority of the output originates).

 

[chausman]

Are the fixtures bench focused the exact same way, and both with perfectly clean optics? Upon examination, are there any noticeable differences between the new and used envelopes? I've seen a bit of translucent cloudiness before, but this generally appears near the tip of the lamp (which is not where the majority of the output originates).

Yes, or as close as one can be. Both were also cleaned very recently, by the same person, the same way.

 

[Beans45601]

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Halogen Cycle in Globe - YouTube

The lamp is equipped with an open tube that permits the halogen gas to be withdrawn and re-introduced as desired. When switched on, the filament is operating in a vacuum. After a few seconds the bulb is observed to blacken; this is caused by tungsten atoms that evaporate from the filament and condense on the bulb wall. Once completely blackened, the halogen gas is re-introduced back into the bulb. It quickly begins to react with the tungsten that has been deposited on the relatively cold bulb wall, and transports it back to the hot filament. The result is that the wall is returned to its original clarity. In this experiment the concentration of halogen gas used is higher than normal so as to achieve the rapid clean-up. In a standard lamp, the speed of the halogen regenerative cycle is much slower, but it operates continuously to prevent the bulb from blackening and thus maintaining a constant light output during lamp life.

Halogen lamps will clean themselves at full overtime. This video shows it sped up (far more halogen gas, I do believe), but it will happen over time. How much time is actually needed, I am not sure.

 

[JD]

Halogen Cycle in Globe - YouTube

Halogen lamps will clean themselves at full overtime. This video shows it sped up (far more halogen gas, I do believe), but it will happen over time. How much time is actually needed, I am not sure.

Thank You Beans. The video clearly shows it can be done. Never had much luck myself, and I tried a lot of tricks on many bulbs over the years. The lamps of the 80's were iodine or bromide. I suspect modern lamps may use more modern gasses!

As to the original question, outside of the aforementioned deposit issue, the lamps should maintain full output up until flash-over day. No noticeable color shift either.