Film-Tech Forum ARCHIVE: Lamp Current

This is topic Lamp Current in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by William Phillips (Member # 1162) on 12-16-2002, 03:46 PM:

Ive just switched lamps from Osram to Ushio and so far am very happy ( the lamp has done 45 hours now in 5 days).
The lamp is a UXL16SCBU 1600watt. I have started the lamp at 85% of the rated 65amps but was woundering when should I turn the lamp up to 100%. Is it over the life or is there a magical figure.
I have always up to now run the lamps at 100% from day 1 , but thought i would try it 85%.

Posted by Andy Muirhead (Member # 712) on 12-16-2002, 07:08 PM:

Hi William

First things first, assuming that when you say you are running your 1600W bulb at 85% of the rated amps, do you mean wattage? If so that would mean your running at 1360W, which seems a bit low for a 1600W. In fact slightly below the recommended level.

To really answer your question, we would have to know how many Volts and Amps you were supplying the bulb. Under running a bulb can be just as catastrophic on longevity than over running. You should really aim for the 1600W mark from day one, I don't believe there's anything to gain by under-running, I imagine quite the opposite.

I'm sure the rest of the guys will pipe in soon, but I think I covered the basics, and If i'm wrong at all, I will admit it!

Also, I haven't heard of the brand your using at all in the UK, There is a reason why most people stick to Osram, LTI, etc! And it's not the prices!

Posted by John Anastasio (Member # 607) on 12-16-2002, 07:22 PM:

I've used Ushio lamps for years, both Xenon and studio lighting products and have always been impressed with the quality. They're not cheap either, Andy!

Posted by Gerard S. Cohen (Member # 994) on 12-16-2002, 08:51 PM:

If I remember correctly, I used to follow the manufacturer's advice by starting a new lamp at 85% of its ampere rating as written on the tester's tag, for the first 25% of its warranteed life. Then bringing it up gradually to 100% amperage (by the lamphouse meter) at
about half its expected life. When the bulb began to develope a slight flicker, I'd raise it to 105% or 110% to correct it. One brand seemed to benefit by rotating at intervals suggested by mfr, but another seemed to work better left in the same position its entire life. I think these were by Christie.
Gerard

Posted by Jeffry L. Johnson (Member # 453) on 12-17-2002, 11:34 AM:

85% first quarter of warranty hours
90% second quarter
95% third quarter
100% fourth quarter

Posted by William Phillips (Member # 1162) on 12-17-2002, 12:03 PM:

Cheers all.
Some time ago I read somewhere that a Xenon`s output dropped by a bit after a certain amount of hours ( bit like the reverse scan LEDs) so starting at 85% or whatever and building upto 100% was a good way of keeping the light output as constant as possiable for the life of the lamp, and to ensure that the magical 16fl could be maintained as close as possiable throught the lamps life.
I cannot remember where and when I read it or if indeed I am going mad. [Smile]

Posted by Jeffry L. Johnson (Member # 453) on 12-18-2002, 04:39 PM:

Here's part of a 1979 December document from Macbeth Sales Corporation (Subsidiary of OSRAM Corp.).

"The low end of the operating current range is only for idling the bulbs at reduced power between reels for relatively short durations. Normal operation should be at a current close to the rated current for which the bulb was designed. Continued operation at low currents causes deterioration of the bulbs' electrodes that could result in premature darkening of the bulb, ignition difficulties and/or decreased arc stability. All of which could decrease the useful life of the bulb.

"To obtain the longest life for all cases the bulb should be operated with at least 80 % of rated current initially and during life increased to at least 100 %. Near the end of life the bulb requires the rated current for proper operation."

Posted by Matt Jahans (Member # 1508) on 12-19-2002, 05:37 AM:

Hello William

I find that there are many different theories practised around cinema circuits with regards to lamp current.

We recommend to our customers the following 'operating' current range:

Start lamps at 85% of nominal current rating and increase as required up to 105% through out life. This ranging I have found to decrease Cathode wear greatly and therefore reduce premature lamp flicker and bulb blackening.

One of the main problems that I come across when visiting sites is that the lamp is operated at one current setting on install and it is then never altered. If that setting is at the lower end of the current range, the foot lamberts drop off as the lamp ages. If it is set at the higher or (as sometimes seen) top end of the range from day one, the lamp suffers excessive cathode wear; causing blackening of bulb and more noticably flicker, caused by the cathode tip fissuring prematurely.

I 'personally' do not advise a 'set' figure of lamp hours vs percentage increase. This works in one's individual screen but different sites have different equipment / screen size or throw so may differ. For example some sites will start at 85% of nominal current and only have to increase to 95% nominal current through out life and still achieve 16fL (with not less than 10% degradation around the edges).

The above example will have a better condition lamp (with regards to wear) than if he/she had increased to 105% just because it was procedure. Other sites will have to utilise the full current range due to different conditions.

I hope this is of help

Best regards

Posted by John Pytlak (Member # 331) on 12-19-2002, 07:07 AM:

Starting at 80 to 85 percent of maximum rated current, and then increasing it to maintain light output is the usual recommendation. But do NOT increase the current beyond the rated maximum for the lamp. [Eek!]

Posted by System Notices (Member # 2357) on 06-23-2004, 08:52 PM:

It has been 552 days since the last post.

Posted by Andrew Shingleton (Member # 2257) on 06-23-2004, 08:52 PM:

Just wanted to get clarification on the difference between the "rated current" and the "maximum current". For example we use (amongst other things) Osram 3K xenons (XBO 3000W/HS OFR). The service card states that the rated current is 100A, and the current control range is 70A-110A. In this thread where people are mentioning percentages of the current to run the lamp at during it's cycle, are they referring to the maximum current (in this case 110A), or the rated current (100A)?

I was thinking that the reference was to the rated current, which would explain how lamps could be run at 105%. However the terms seem to be used somewhat interchangeably.

Thanks! [Smile]

Posted by David Ingalsbe (Member # 2433) on 06-24-2004, 04:28 AM:

From what I have been told on xenon lamps its the wattage that is the most important thing not the current. Voltts times amps equals watts or ExI=W. Our Strong rectifiers only put out 20-25 volts so 22 volts times 117 amps equals 2574 or about 85%. If anyone can correct me I would apriciate it. [Smile]

Edit I also run Osram XBO 3k's but like Christie 30R's. [Big Grin]

Posted by John Pytlak (Member # 331) on 06-24-2004, 05:40 AM:

quote: Andrew Shingleton
The service card states that the rated current is 100A, and the current control range is 70A-110A. In this thread where people are mentioning percentages of the current to run the lamp at during it's cycle, are they referring to the maximum current (in this case 110A), or the rated current (100A)?

That lamp was designed to run best at 100A. Output will become unstable below 70A, and it should never be run above 110A. Base your calculations on an aim current of 100A.

Posted by Ferdinando Innocenti (Member # 2477) on 06-24-2004, 10:32 AM:

David,
it is not true! you must use right rectifier with right lamp. An Osram XBO3000HS has a rated voltage of 30 volts, and a rated current of 100A. Current is function of electrons charge, so it must be set below the maximux current in the data sheet.
Are you really using a 3000W lamp with a 22 volts rectifier?

Nando

Posted by David Ingalsbe (Member # 2433) on 06-24-2004, 02:11 PM:

yes I have a 20 plex and I think only one projector puts out 29v.
all lamps that I have ever seen have a test of 29-30 volts. SO the next thing is is there any way to incress the voltage on a strong high reactance power supply used in a Highlight II. Most of mine tested with a volt meter at the output are 23-26 low of 22 high 29. [Frown]

Posted by Andrew Shingleton (Member # 2257) on 06-24-2004, 06:09 PM:

Thanks for the info John. [Smile]

I've devised a forumula which I intend to use to help with the process of gradually increasing current throughout the lamps life. I plan on installing the lamps at 90% of their rated current (which in most cases is between 80-85% of it's maximum current), and then using this formula to calculate the ideal amp setting to adjust to each week. The result of following the formula will be a steady increase in amps throughout the first 4/5ths of the lamps warrenty period, reaching rated current at 80% and remaining there for the remainder of the useable life.

(r*0.9)+((r*0.1)*(p+(p*0.25)))

r = rated life in amps
p = percentage of rated life completed (expressed as a figure between 0 and 1).

There is also a qualifier that if the total of (p+(p*0.25)) is greater than or equal to 1, then r should be used instead (this will prevent the formula from telling me to use a current higher than the rated current). As an excel formula the shows as:

=IF(p+(p*0.25)>=1,r,(r*0.9)+((r*0.1)*(p+(p*0.25))))

(replace p and r with cell references)

Now if I've explained that properly and anyone's actually still on the same page as me, I was just wondering if there were any glaring flaws or problems with this formula, or more importantly with the method of xenon use that the formula facilitates? We intend to take xenon hour readings each week and then enter the data into a spreadsheet, which will use this formula to give a printout of the ideal current settings to be adjusted on a weekly basis. [Smile]

Posted by Gordon McLeod (Member # 33) on 06-24-2004, 10:52 PM:

It is a bit of a non issue as long as neither the voltage rateing and current rateing are not exceeded you are ok