Question on Ballasts in fluoros

[Michael Panfeld]

OK so I can now share something with you. I had purchased several 6-bank oriental fixtures. I, being prone to experimenting and looking for cheaper alternatives, purchased some 5500K lamps from alzodigital.com. They were dirt cheap and came with free shipping on orders over $100. So far so good.

I put them in the fixtures and took out my handy Minolta Color Meter II. I got an average temp of 8,000. Yes, I said 8,000. I measured individual lamps and got temps that ranged from 7500 to 8800. Also also found them to be very very green. a -11 on the meter, which is close to a full minus green.

Now I had originally started this thread to see if somehow it was the ballasts that were causing this huge gap. The conclusion sounded like the ballasts may have an affect, as would thermal temperature, but that its mainly the tube.

So on that note, I bought a slew of Kino Flos. They came today and, hit the fricking correct temp at start up. magenta/green reading was a -5. Not bad. I expect that after burning in for 100 hours, I will get some more stabilized and less green results.

Just goes to show you: save $$$ on cheap fixtures but don't scrimp on lamps.

Cheers

[Bob Grant]

Originally Posted by Michael Panfeld

OK: so I found this in a Kino Flo brochure. You were right.

The physical heat of the lamp directly influences color temperature and lumen performance and lamp life.
In order to maintain a stable color performance the lamp requires:
a cool spot at the tip of the lamp
a horizontal orientation
or a vertical orientation where the base of the lamp is above the lamp tip.

The industry standard (used by Lowell, Arri etc) Osram Studioline tube is spec'ed to burn in any position:OSRAM Studioline 55W

I'm a bit nervous about KinFlo fluro lamps. We've got a Kino 800 and the tubes in that run very hot. A 6 foot tube handling 100W is pushing it. Those tubes have the option of a plastic safety sheath and not only does that affect the cooling, over time it bubbles up at the ends of the tubes.

A fluro tube should have a usable life of around 8,000 hours. I've run the Osram 55W tubes in an outdoor sign for over 20,000 hours at around which point there's just no mercury left in them. Needless to say before that the CT was getting a bit off but it is just a sign :)

[Bruce Watson]

Originally Posted by Bob Grant

A fluro tube should have a usable life of around 8,000 hours.

Yes, but is this a useful life for cinema lighting? I've read that both color temperature and CRI change as the tubes age. Many cinema lighting people seem to change out bulbs every year or so just to maintain a constant light quality.

Has anyone done any testing for this? IOW, is this a real problem or just a myth? The only way to tell would be to do the experiments (I don't have the space or the equipment) and chart the changes over time. I'm sure it's been done and probably published. But I've not seen such results yet. Anyone?

[Michael Panfeld]

Bruce: The Kino document which I previously cited states that the useful life for film work is more realistic than the full 8K hours. Kino says its around 2500 hours.

BTW, thanks to all for sharing your thoughts and making this a lively discussion.

[Robin Lambert]

Just about every broadcast studio I work in has Kinoflo tubes, even if they have other units. There doesn't seem to be a "standard" period after which they're changed. I just go in, fire 'em up and then point out the tubes (if any) which are a different colour to their neighbours and get them changed.

So I would guesstimate that they last a maximum of 5000 hours before they start to change colour. Kino are probably covering their bums when they quote 2500 hours. They may well go on for another 15000 hours but by that stage you would have a mulicoloured grid up there.

There is no doubt that Kinos are the most accurate, followed by Osram Studiolines. Place the two in the same unit and you can see the difference, with the Osrams looking slightly green in comparison. For the sake of a few dollars, it's worth getting the Kinos since they will mix with tungsten lamps (I mean, of course, the 2900 or 3200 tubes) or true daylight without any filtration.

[Bob Grant]

Originally Posted by Robin Lambert

Just about every broadcast studio I work in has Kinoflo tubes, even if they have other units. There doesn't seem to be a "standard" period after which they're changed. I just go in, fire 'em up and then point out the tubes (if any) which are a different colour to their neighbours and get them changed.

So I would guesstimate that they last a maximum of 5000 hours before they start to change colour. Kino are probably covering their bums when they quote 2500 hours. They may well go on for another 15000 hours but by that stage you would have a mulicoloured grid up there.

There is no doubt that Kinos are the most accurate, followed by Osram Studiolines. Place the two in the same unit and you can see the difference, with the Osrams looking slightly green in comparison. For the sake of a few dollars, it's worth getting the Kinos since they will mix with tungsten lamps (I mean, of course, the 2900 or 3200 tubes) or true daylight without any filtration.

The Osram tubes can be had in both daylight and tungsten. Both Osram and Kino tubes have a green spike, Kino's own spectrographs clearly show this. I cannot find the graphs for the Osram tubes online at the moment.
Color shift over time is a common problem for all discharge lamps, HMIs shift around 1 deg per hour.
The Osram Studioline tubes are not Osram's highest CRI tubes, they do a better range of lamps for museums and art galleries but they don't come in a 55W version. Generally the Studioline tubes are considered more than adequate for video but not good enough for film.

If it was simply a matter of using Kino tubes in the same instruments to feel better about your lighting I'd say go for it. The issue I see is only Kino's instruments are designed to meet their requirements for lamp orientation. The Lowell and Arri instruments that are pretty common in studios down here and the Lupo instruments out of Europe that we use plus all the Chineses cheapies all have the lamp base down, base up and down or base level with tip. That is fine with the Osram tubes however Kino are very specific about not running their lamps in any of those orientations. That might just be FUD however the Kino lamps do appear to have subtle differences in their design compared to the Osram tubes.

[Robert Turchick]

So I'm starting to get serious about fluorescents and like many out there can't afford to buy 6 kino flo fixtures. Looking at them, there seems to be a lot of added electronics and dimming which I just don't need.

My end purpose is to permanently light a green screen that will be 12' wide, 9' tall, and have a 9' floor, all paint with the cyc transition from wall to floor.

I recently was told about Kino's 4' T12 75 watt green screen bulbs and they sound like the ticket. Curious about mounting in a cheaper shop-light style fixture re-ballasted properly. I will be making my own mounting brackets and barn doors too. And painting the fixtures matte black and putting in a silver reflector too. I have found electronic ballasts at the proper rating for about $40, fixtures for about $30 and the bulbs are about $120 for a six-pack. Seems like a deal if it works! Just curious if anyone has had luck trying this. Especially curious about the green screen bulbs!

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