Can you over cool a bulb?

[Frank Raia]

Can you over cool a bulb? I can not find clarity on this from old posts in the forum.

My bulb is small. 1600w in a Cinemeccanica CX-900 vertical lamphouse. I upgraded my exhaust fan to a 800 cfm fan. The exhaust from the fan never even gets warm. My old fan that was 400 cfm would blow out warm air.

Is this good or bad?

[Josh Jones]

I was always told the more air the better. I have also heard that too much airflow can disturb the gas currents in the bulb and cause flicker. I'm not sure if that true, or just an old wives tale.

[Jim Cassedy]

I know correct airflow was an issue back in the carbon arc days. (I had sudden gusts of
wind during summer thunderstorms extinguish my arc, despite the presence of 'downdraft
diverters) . . and I too have heard the 'tale' about too much airflow disturbing the arc
inside the bulb that Josh mentions and don't know if it's true or just B.S. I would guess
that the only danger would be how 'cold' the air being drawn into your lamphouse is. For
example, if you're lamphouse was close enough to an air conditioning unit or vent so that
very cold' air was being sucked into the bulb chamber, there might be a risk of the bulb
shattering. But that's totally a wild guess. I don't know enough about how much temperature
differential a quartz bulb envelope can take before stress would cause it to break.
Like Josh, "the more air the better" is what I've always heard, as long as you avoid
extremes, I guess.

[Josh Jones]

I would think sudden large changes in temperature during operation would be a greater danger than the actual temperature delta.

[Randy Stankey]

IMO, if airflow is consistent throughout the operation of the lamp, things should be okay. It is sudden changes in airflow that can cause problems.

If the lamp starts out cool, then gradually warms up while air is moving around it, the glass and metal will expand and contract gradually and evenly. There shouldn't be any problems with heat/cooling induced stress. But, if the lamp is hot when there is a sudden change in airflow, that could cause problems.

While I am sure that there are upper and lower limits to the amount of airflow that is necessary, I think that range is fairly broad, provided all other things stay consistent.

[Ryan Gallagher]

Lots of air can also vibrate or shake things in unintended ways. Doubtful it would be a lamp issue, but overall picture steadiness might suffer. I know I can see evidence of our exhaust oscillations/vibrations on our 118ft digital throw if I am right next to the screen.

[Tony Bandiera Jr]

Based on my decades in this biz and servicing many hundreds of screens...the answer is..... definitely maybe.

Some of the early Osram and ORC lamps (1980's era) seemed to be sensitive to excess exhaust airflow, and a slight, but noticeable wavering of intensity could be seen, in some cases. It was almost always subtle and really only noticeable in bright scenes. I was able in a few cases to verify that issue by adjusting the dampers (when present) or by gradually lifting the exhaust hose off, introducing a deliberate "air leak" to reduce the cfm's through the lamphouse. Those same locations stopped having that issue in the following 5-10 years, so....

Also the problem was more of an issue in the home screening rooms with the 500w Xenons. But those bulbs were always finicky.

In later years I never saw the problem crop up, so it could have been something other than airflow on those problem locations, or maybe bulb manufacture and gases improved.

So I'd say it was possible, but really more of a nothing burger than anything to worry about.

[Thomas Piccione]

By the books, yes, you can. Osram did give a spec for it, but frankly, I'm not sure I would enjoy testing for it. Per their XBO Theatre Lamps pamphlet, "If the lamp voltage with cooling falls by more than 1 volt compared with uncooled operation, this normally means that cooling is excessive." They give the same reasoning that Josh mentioned; excessive cooling will cause instability of the xenon gas inside the bulb. Is that something you can realistically achieve in most lamphouses? Maybe, maybe not. You could test for it, or if you're not getting excessive flicker, let it ride.

[Frank Raia]

Follow up...

I contacted Christie in regards to over cooling, and this is the response they provided:
"The minimum exhaust CFM for a 35mm Xenon console lamp house typically ranges from 300 CFM to 500 CFM."

They also provided a manual for their SLC Series Consoles. It states:

4.2.3. VENTING
It is necessary to vent hot exhaust air from console to the outside of the building.
1. Connect a eight-inch inner-diameter, flexible, fireproof ducting material to exhaust duct
(Item 1 in Figure A-2) on top of lamphouse.
2. Ensure that there are no obstructions in ducting, and that air intake openings of console
are unobstructed.
If ozone-free lamps are used, a short, vertical exhaust stack may be used, provided local
codes do not require the exhaust to be vented directly outside.
Minimum and maximum exhaust airflow requirements for all SLC series models are shown
in Figure 4-3.
Model Minimum Exhaust (ft3/min) Maximum Exhaust (ft3/min)
SLC 20 300 400
SLC 30 350 450
SLC 40 450 550
SLC 45, SLC 45R 550 750
SLC 70 750 900
Figure 4-3: Minimum and Maximum Exhaust Airflow Requirements for SLC Consoles

I also contacted Ushio, because Osrams website directs to Ushio for cinema lamps. I did not receive any response from them.

I did find an Osram Bulb Info publication in the Film Tech warehouse. This is what it says:
image.png

So I guess over cooling is possible

[Mark Gulbrandsen]

Lamp Manufacturers all specify a recommend CFM to cool a given lamp... So you should look up the lamp on the manufacturers web site, or if you don't find it there give them a call. You can also buy relatively inexpensive air flow meters to verify it...

[Tj Hopland]

The advertised cfm rating of a fan is usually basically hanging in free air with no duct work attached to it. You start loosing flow when you start connecting duct. How much you loose depends on a lot of factors like the size and finish of the duct as well as bends. A quality fan from a quality make may have some charts showing the losses at different pressures which I assume if you learn how to calculate at HVAC school. You talk to the typical HVAC person and say you want 800 cfm they are gonna say you need a minimum of a 12X12 duct and that will be smooth and straight and not very long. To try and pull 500+ cfm through something like a 6" pipe is getting into like dust collection levels, not really ventilation so the guys would freak out when we said we wanted lots of air on the older stuff that just had a 6" pipe. Equipment moved into 8" pipes in the 80's to help that but as a HVAC guy pointed out with a machine I was working on today it kinda looks like they just stuck that 8" on the top and doesn't seem like they really have 8" worth of inlets to really allow for that high of a flow.

CX-900 has what a 5" ish probably metric pipe on it and presumably enough inlets to support that? Its been just a few years since I worked on one but I was thinking it was smaller than a 6". HVAC will say that's good for about 150 cfm. So if you stuck a 800 cfm fan on that you won't be getting anywhere near that kind of flow with all the likely restrictions you have in there. You may also want to check the current draw on the fan motor to make sure its within limits. As mentioned above that fan was likely designed to be hooked to like a 16 round pipe. Trying to make it suck through smaller ducting and that little lamphouse cold be making some wacky fluid dynamics happen so you want to make sure you are not working the motor too hard.

[Will Kutler]

As Mark stated, lamp house tech manuals like Christie specify the exhaust fan CFM requirements based on Xenon wattage to optimize bulb performance and life. Exhaust requirements also applied to carbon arc to help control the arc flame.

[Gordon McLeod]

Can you over cool a bulb? I can not find clarity on this from old posts in the forum.

My bulb is small. 1600w in a Cinemeccanica CX-900 vertical lamphouse. I upgraded my exhaust fan to a 800 cfm fan. The exhaust from the fan never even gets warm. My old fan that was 400 cfm would blow out warm air.

Is this good or bad?

The cx 900 lamphouse is rated for a maximum of a 900 watt lamp not a 1600 wat lamp the igintor cant handle that much current. Yes on can over cool a xenon lamp making it blacken prematurely as well as be unstable
The CS 900 was supposed to have around 300 cfm of exhausr