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Fluorescent Lamps, their Kelivn values

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December 20, 2005

I'll assume you have the basic tables for correction of major types of tubes. If not, you can find a color correction wheel (for flourescents and HID sodium vapor, etc. in the Kodak Professional Photoguide. Since Kodak's tables are based on the color temp of the film and not specific type, they're a good starting point for films by other manufactuers like Fuji and Agfa.

Since there are so many tubes made by different manufacturers, (cool to warm) as you have probably realized, a color temp meter for critical corrections is the way to go but depending on your lighting situation and for reasons I'll get to in a second, they're still not always completely accurate. Besides, the cost of all color temp meters is pricey, but what'll REALLY kill ya is the cost of the cc (color correction filters) that you use to get to the temp you want depending on the film you're using. My own preference is the Hitech system. Their cc's are resin and at least reasonable in cost. As for meters, it depends on the type and for the best price on new ones, look at http://bhphoto.com (or bhphotovideo.com)

In addition, rather than Kelvin, for practical purposes in photography, a more useful scale to rate flourescents is the CRI or color rendering index. The CRI uses high-noon daylight as a standard with a rating of 100. So, a tube rated at CRI 90 or 91 has either a 90 or 91 per cent color accuracy when compared to daylight. In essence, the higher the CRI, the more accurate the color is to daylight.

Still, for most film work you can ball park the correction if you generally know what kind of tube you're up against without knowing it's actual temp in relation to daylight according to the film you're using.

For example, if you shooting "warm white deluxe" tubes on Ektachrome daylight, your correction would be about 60 cyan plus 30 magenta and add 2 stops to your exposure.

And as you may also know, flourescents pulse according to 60hz current we use in the U.S. So, longer shutter speeds are required shooting flourescents because faster speeds will leave some of the lights looking dark or even black depending on their frequency. AND your correction will also depend on the specific glass coating along with the age of the tube which, of course, that's really impossible to determine, so what it comes down to again, is using a color temp meter to see more precisely where your actual lights are at.

If you really want to make your own compendium of K temps then I'd suggest going to the websites for each manufacturer, pull up the product literature for each lamp they make and you'll find the K. temp. for each brand name they make and the variations of that brand. For example, take a look at Sylvania's site:
http://www.sylvania.com/BusinessProducts/ProductLiteratureDownload/Product+Literature/Fluorescent/

Each product sheet lists K. for each lamp. The manufacturers might even be able to provide you with a temperature chart for their products, but then you're going to spend a lot of time climbing around on ladders popping ceiling baffles, removing and rotating tubes to see if you can still read the labels on them.

Also, remember that while you may be shooting a bay of flourescents in a ceiling, not all the tubes may be of the same kind and thus not precisely the same temp. That diversity is going to prevent exact correction. That's another reason why I tend to ball park the correction, bracket and adjust my filtration based on daylight temp/ color test shots.

Even worse is when you're working in say a factory with HID sodium vapor or mercury vapor lamps mixed with flourescents against windows illuminated by daylight. Now what? I usually try to correct for the dominant light source, say a hail mary and let the others just go. Then I'll shoot a few frames or sheets bracketed by 1/2 a stop either side of center and without correction.

After awhile, you can stand back and pretty much see the basic color of the lights, like warm, cool, pure white, pink, warmer yellow, green, or if they put out a bluish cast.

Lastly, you can actually get flourescents to near daylight temp by washing the ceiling (usually white) with 5500K electronic flash set in a high-key reflector off camera.

Hope this helps.
Take it light.
Mark

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December 20, 2005

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December 20, 2005

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December 21, 2005