Film-Tech Forum ARCHIVE: Leaving a digital projector on with the douser/shutter closed

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Posted by Alexis Mayer (Member # 3967) on 04-19-2012, 04:32 PM:

Is leaving a digital projector on with the douser/shutter closed bad for the projector? If so, how exactly? Is there a limited amount of time where it would be okay?

Thank you in advance for your insights!

Best,
Alexis Mayer

Posted by Justin Hamaker (Member # 2165) on 04-19-2012, 05:15 PM:

In theory, you don't want to leave the dowser closed with the lamp on for any extended period of time as the heat can damage the dowser. In reality I've found there doesn't seem to be enough heat making it from the lamp to the lens to make this a serious issue - at least not with the NEC NC2000 projectors at my theatre.

The bigger issue we've found with the dowser is that it won't always open on cue as it's supposed to. We leave it open 100% of the time, other than when the projector automatically closes it as part of the lamp on sequence.

Posted by Monte L Fullmer (Member # 2797) on 04-19-2012, 05:39 PM:

You'd think with the cost of bulbs and how fast they fade when they get the hours on them that you'd want to turn the bulb off between presentations making the douser issue not an priority issue here .

Posted by Victor Liorentas (Member # 5272) on 04-19-2012, 06:16 PM:

But then the ignitions to the bulb increase...

Posted by Antti Nayha (Member # 4980) on 04-20-2012, 02:58 AM:

According to Ushio, it’s better to turn off the lamp between screenings than to keep it on the whole day:

quote:
Operational Note for Digital Cinema Xenon Lamps:
Based upon our internal research experiments, operation cycles with "On/Off" mode every 2 hours (10 minutes off), delays the generation of lamp flicker by up to 30% when compared to the operation cycle of 11 hours continuous mode.

Posted by Brad Miller (Member # 2) on 04-20-2012, 04:10 AM:

Keep in mind the bulb must FULLY COOL before it is struck again or it is doing quite a bit of damage. That also, from Ushio.

A 10 minute MINIMUM down cycle was their recommendation. If it can't be down for at least 10 minutes, it is far better to leave it burning.

We have already incorporated this cool-down timeframe logic into the DCS as an option that can be enabled at the customer's request.

Posted by Eric Robinson (Member # 2966) on 04-22-2012, 10:19 PM:

I wonder what the effect is on the switching power supply or rectifier regarding continuous or on/off operation.

Posted by Robby Golosino (Member # 6325) on 05-04-2012, 07:23 PM:

Well,for me,its better to turn the lamp on and off every screnning for 3 small reasons.1st,to save the life of xenon as long as it can be,2nd xenon is more valuable than the rectifier,3rd is to avoid from being scolded by my superior,lol.

Posted by Dave Macaulay (Member # 813) on 05-04-2012, 08:45 PM:

I guess it depends on the projector. Christie has the dowser before the light processor, so it can probably stay closed with light on forever. Barco and NEC have the dowser after the light processor, just behind the lens. Barco says not to project a test pattern or non-black image on the dowser to avoid damaging it I think. I don't know about NEC. A "black" image passes so little light I can't see it causing trouble with the dowser.

Posted by Randy Stankey (Member # 64) on 05-04-2012, 10:02 PM:

As far as leaving lamps burning, my rule of thumb is that one strike of the lamp equals one hour of burning time.

Thus, if the lamp is going to be off for more than an hour, turn it off. Otherwise, it's probably better to burn it.

YMMV.

Posted by Joris Springer (Member # 4175) on 05-10-2012, 05:07 PM:

Turning the lamp on and off between shows is something I think lamp production companies have probably calculated in when they made the bulbs, I mean why sell lamps that have less than 75% of their guaranteed life span?

But the dowser, I noticed that there was a difference between the DP100/DP90 and the DLP2K/DLP4K series, it seems that there is not really a physical dowser but that it is just projecting black picture. Or the dowser has gotten really quiet [Smile]

. I mean on the DP100 and 90 series I could just hear it open and close and now not anymore.

Anyway, we turn of the lamp after every show though when there is a very short time between the movies we keep it now on.

Posted by Steve Guttag (Member # 268) on 05-10-2012, 06:19 PM:

I believe the physical douser is part of the DCI spec (would have to spend the time to check and don't feel like it now). That said...every DCinema projector I've worked with has a physical douser, including series 2s...projecting black does not work in mixed venues where multiple projectors are needed (could even be film and digital) because "black" is not really black.