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Old October 26th, 2006, 02:17 PM   #1
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Practical Light Color Temp

The video lights I use are 6500K fluorescents. I also carry some additional 6500K compact fluorescents to re-lamp and overhead fixtures as required to modify the base light level. I am curious if there is a standard textbook answer on what color temp the practical lamps that appear in the frame should be. When using 6500K illumination a tungsten bulb or tungsten balanced fluorescent appears very yellow.

I imagine I could watch some TV and do my own homework, but I thought someone that does professional lighting might have the textbook answer for this problem.
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Old October 26th, 2006, 02:20 PM   #2
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Work lights and bulbs are around 2800K. Tungsten lights are 3200K. Fluorescents really do not have a color temperature, so they can look peculiar no matter what color temperature you set your camera to. As you probably know, they use a rating called the CRI--the higher, the better.
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Old October 26th, 2006, 03:21 PM   #3
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Well, it depends how you're white balanced. If you balance to a white card that reflects only your fluorescents, then the camera is balanced to "6500K." To be neutral, everything in the frame should also be 6500K. To be warmer, the lights in the frame should be <6500K, or to be bluer (colder) they should be >6500K.

The "textbook" answer is... it depends. Most lighting was initially created in the film realm, where color temperature can't just be white-balanced. Basically 2 types of stock exist - daylight and tungsten. Daylight (roughly 5600K) and tungsten (roughly 3200K). You balance and filter your lights to the stock you're using. With video "white balance" this is less important, though you still need to balance the lights to eachother. White balance essentially tells the camera what color temperature film stock it is.

Now, that said, this can be confusing when you're referring to fluorescents. Emre is right that the "CRI" or color rendering index is important when dealing with flo's. Color temperature is literally the temperature at which a carbon black-body must achieve to radiate a certain light. This means a glowing filament basically. Fluorescents are mercury gas-cloud arc sources, so they don't have glowing filaments and thus stay WAY cooler, make more output, but also don't perfectly apply to the notion of "kelvin temperature." Fluorescents produce an incomplete spectrum, and they have a notably large "spike" in the greens. This is partly because of the mercury, and also because our eyes are more sensitive to green light, and it's an easy way to boost output and brightness without upping the energy too much. Our eyes naturally color-balance the green out until the tubes get very old and start REALLY kicking in the green. CRI is basically a measure of how well a lamp can render color accurately. In the case of fluorescents, it tells how closely the tube can produce a full spectrum of light.

SO...

If there is any way to relamp your fixtures closer to 2800 or 3200 K, you'll find it a LOT easier to balance to indoor practicals. Very few indoor fixtures try to hit "daylight" balance, because its very simple and cheap to use incandescent or tungsten halogen lights, which like Emre mentioned, are very close to 3200K. Filtering those lights cuts the output down to about 12%! Very inefficient to make a non-daylight source balance to daylight.

If you want to be very exact, there is something called the mired scale which makes it easier to understand how "off" certain light temperatures will look from each other. Divide 1,000,000 by the kelvin temp and you get the "mired" value. 3200K = 313m. 2800K = 357m. 5600K = 179m. 6500k = 154.

From 5600-6500 = 900K = 25m
From 2800-3200 = 400K = 44m

What does this mean? That differences in color temperature are WAY less noticeable in the blues (daylight) than in the reds (tungsten). It's a LOT of info, but this should give you some info from which to make decisions. If it's still confusing, ask more questions!
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Old October 26th, 2006, 07:49 PM   #4
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Yah', something's got to change color temp.

Maybe you can get a little cylinder of full or half CTB gel into your practical.

Cheap, easy, and might work... good enough. A full sheet of CTB would be less than $7, and you could probably correct 4-6 practicals with it.

Or, you can take some CTO to your fluorescents.
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Old October 27th, 2006, 11:07 AM   #5
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Changing the color temp of the practical light is usually as easy as unscrewing the 60 watt tungsten bulb in the fixture and replacing it with a spare 6500K compact florescent I carry in my kit.

The meat of my question was really should I carry 3200K lamps for effect (to create yellowish looking practical lights) or is it proper to have everything the same color temp. To answer a previous comment, I always white balance with my studio lights only, before turning on any practical lights.

It looks like the consensus is that everything should be light with the same temp lights so this is what I will do. Thanks for the advice.
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Old October 27th, 2006, 11:20 AM   #6
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There is nothing wrong with warm practicals. People expect them to look yellow. It is up to you.
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Old October 28th, 2006, 10:50 PM   #7
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Quote:
Originally Posted by Emre Safak
There is nothing wrong with warm practicals. People expect them to look yellow. It is up to you.
Absolutely. If you were filming a detective grilling a suspect with the desk lamp in his face, you would probably want to be harsh and white, say in the 4-5000K range. If on the other hand you a filming a romantic scene, or something to feel good and cozy, you would probably want it warmer and use the 60 watt GE bulb that's already in those table lamps.

It's all about feel, without letting your in and out-of-scene lighting become the centerpiece and thus, a distraction. Rent and view "The Sixth Sense". Everything in just about every shot (especially the ones with Bruce Willis in them) are blue. You don't really notice unless you are looking. Blue interiors, moonlight, and sunlight. Of course, it's because the Willis character is dead and doesn't know it. And director M. Night Shyamalan wants to subliminally creep you out. You say to yourself, "...something's wrong here, but I can't quite put my finger on it".
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