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Tungsten or gels?


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#1 Jeff Webster

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Posted 12 February 2007 - 04:06 AM

Say I want a shot that has a warmer feel to it. What is better or what is the difference between using tungsten lamps with 5200K white balance versus HMIs with CTOs or CTSs with the same 5200K white balance?
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#2 David Mullen ASC

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Posted 12 February 2007 - 10:52 AM

Say I want a shot that has a warmer feel to it. What is better or what is the difference between using tungsten lamps with 5200K white balance versus HMIs with CTOs or CTSs with the same 5200K white balance?


You mean 3200K, not 5200K.

3200K is tungsten-balance and 5500K is photographic daylight-balance.

But whether the shot looks warmer or not depends on what is "white" for your film stock and scene.

On tungsten-balanced stock, a 3200K tungsten lamp is "white" not warm, and a 5500K HMI is very blue-ish. But on daylight-balanced stock (or tungsten-balanced stock with an 85B correction filter on the lens) then an HMI looks white and a tungsten lamp looks very orange.

So starting with that in mind, what is your question? Are you asking whether there's a difference between using an ungelled tungsten lamps versus an HMI with Full CTO/CTS correction gel on it? Yes, somewhat, in only that tungsten lamps are very consistent in color whereas HMI's are a bit all over the map in terms of color bias and some even have a slight greenish tint, so if you want 3200K, generally you'll get better results with a tungsten lamp. Plus HMI's are finnicky; they can have restrike problems, flicker problems, etc. Plus you can put tungsten lamps on dimmers.

However in a daylight-balanced scene, it's not uncommon to warm up an HMI to create a late-afternoon look, like with 1/2 CTS for example, mainly because it's more flexible to light a day scene on location with daylight lamps and gel as needed for extra warmth. However, if you get into a night interior and want 3200K, then you'd use tungsten lamps.

Sometimes when you know you want a 3200K color in a daylight scene for a sunset effect, you may roll out a big tungsten lamp instead of gelling an HMI with Full CTO/CTS.
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#3 Hal Smith

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Posted 12 February 2007 - 12:26 PM

........Plus you can put tungsten lamps on dimmers.......

Have you ever seen a table listing color correction gels for dimmed tungsten lamps? It would list percent dimmed versus a CC/CTB series gel, etc. That way one could dim to say 80% and know what gel to put in front of the lamp to bring it back up to 3200K without having to drag out a color meter and fiddle with gels. Final light output would obviously be a function of dim percent and gel loss
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#4 David Mullen ASC

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Posted 12 February 2007 - 12:33 PM

Have you ever seen a table listing color correction gels for dimmed tungsten lamps? It would list percent dimmed versus a CC/CTB series gel, etc. That way one could dim to say 80% and know what gel to put in front of the lamp to bring it back up to 3200K without having to drag out a color meter and fiddle with gels. Final light output would obviously be a function of dim percent and gel loss


Would the type of dimmer affect that? The type of tungsten bulb (a large 10K globe versus a 650w globe)? I'm not sure. I tend to do it by eye.
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#5 Hal Smith

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Posted 12 February 2007 - 01:14 PM

Would the type of dimmer affect that? The type of tungsten bulb (a large 10K globe versus a 650w globe)? I'm not sure. I tend to do it by eye.

Good questions.

The dimmer type's waveform (SCR versus Variac, etc) shouldn't be the core issue. The RMS (root mean square) power of the dimmer's output, not the waveform's shape, is what determines filament temperature and therefore color temperature.

Most modern dimmer packs use a modified square law ratio dimmer law between the percentage of dim on the controller versus what actually goes out to the lamp. The exact ratio of controller percent dim output versus RMS power output could be and probably is a variable from manufacturer to manufacture. To be certain about what's actually going out to the lamp for a given pack's dimmer law it would be simple to take a look at the actual voltage with a true RMS voltmeter like a Fluke 87 and build a table.

I'm not too certain about the effect of the size of the bulb on color temperature versus RMS power . My gut instinct is that it isn't, tungsten is tungsten and a given percent RMS power should be the same blackbody radiation filament temperature for various size lamps but I don't have any hard information about that. An email or call to someone in Engineering at GE Lighting should get an answer about that. At the worst, an RMS power versus color temperature chart would be necessary for each type of bulb. Obviously that would complicate the situation but for such a set of tables to exist, they'd only have to be worked up one time. If I had a Minolta Colormeter I'd be tempted to try and build up a few tables myself. Once one had a good set of tables one could use the Mired system to figure out color correction.

If this information doesn't already exist, and if you think it would be valuable to the profession, I'll try to scare up a color meter and have a go at getting some hard data. I'm starting to get Deja Vu all over again, my degree is an MS in the Teaching of Physics and this is starting to feel like a Physics lab project. I'm already halfway back into my old lab at Sewanee trying to beat Physics into the student's heads. :)
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#6 Chris B. Cornell

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Posted 16 February 2007 - 03:27 PM

Good questions.

The dimmer type's waveform (SCR versus Variac, etc) shouldn't be the core issue. The RMS (root mean square) power of the dimmer's output, not the waveform's shape, is what determines filament temperature and therefore color temperature.

Most modern dimmer packs use a modified square law ratio dimmer law between the percentage of dim on the controller versus what actually goes out to the lamp. The exact ratio of controller percent dim output versus RMS power output could be and probably is a variable from manufacturer to manufacture. To be certain about what's actually going out to the lamp for a given pack's dimmer law it would be simple to take a look at the actual voltage with a true RMS voltmeter like a Fluke 87 and build a table.


Wow, great info. It is nice to see a DP who really seems to know the ins and outs of the technology at use. I have worked for some gaffers and DPs that use a color meter a lot, and I have worked for others that seem to do it all by eye. As far as HMI vs. tungsten; tungsten seems to have more favorable quality's. There is no noisy ballast, magnetic ballasts usually don't allow for variable frame rate shooting, electronic ballasts are generally not user serviceable, the HMI globes tend to not always hot strike. There are various other technical arguments over the two, and I have heard that many DPs prefer tungsten because the light has a "warmer" more favorable quality, and does not flicker, I am not experienced enough to really make this call myself however, if anyone else wants to chime in....
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#7 David Mullen ASC

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Posted 16 February 2007 - 04:25 PM

chrisbc, you need to edit your Display Name (go to My Controls) to be a real first and last name, as per the forum rules. Thanks.
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