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Old August 19th, 2011, 11:58 AM   #1
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White Balancing for inactinic (yellow) light.

I have an upcoming shoot in a lab which is lit with photo-sensitive safelight (inactinic spectrum). Anyone have any suggestions on how to correctly white-balance for yellow inactinic light (photo-sensitive safelight). Would just using a white card for calibration work or does it require a specific lense filter?

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Old August 19th, 2011, 09:23 PM   #2
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Re: White Balancing for inactinic (yellow) light.

Found on the web:

SAFELIGHT FILTERS The word safelight in photography is used to describe filtered tungsten illumination or direct illumination from a sodium-vapor lamp. The color of a sodium-vapor lamp does not affect (expose) light-sensitive materials under prescribed darkroom conditions. The word safe is misleading since light- sensitive materials are never completely safe from safelight illumination. The use of a safelight with some types of light- sensitive materials is not recommended Compatible safelight filters for use with certain light-sensitive materials should be selected on the basis of color sensitivity and emulsion speed of the material. The best method of selecting a darkroom safelight filter is to use the filter recommended by the manufacturer of the light-sensitive material. Safelight filters absorb that portion of the visible spectrum produced by a tungsten lamp that would affect the light-sensitive material being handled.

Sodium-vapor lamp safelights use sodium gas to provide safelight illumination. Incandescent sodium gas produces a very narrow band of visible light in the yellow-orange portion of the spectrum. Colorblind printing papers are not sensitive to this monochromatic (one color) band of light, whereas the human eye is very sensitive to it. Therefore, a brighter print room is possible without the light affecting the printing paper. By using specially designed filters that further reduce the narrow band of sodium-vapor light, black-and-white materials sensitive to green and red light can be handled under this illumination. Table 3-7 provides some examples for the application of safelight filters. Always consult the Photo-Lab-Index to determine the best safelight for use with various light-sensitive materials."

Darkroom Filters

It appears to me these are the two types of bulbs used, Tungsten and Sodium Vapor. Kelvin on those would be 3200K and it looks like about 2700K, respectively. As I was looking around about this someone on Yahoo Answers suggested using an Expo Disc, the white balance lens cap thingey.

If it were me and I was going in with my GH1 I would go to the numeric settings for Kelvin and tweak it in the areas of these two types of bulbs until I got whites that I knew were the right shade of white. Best scenario would be to do a test white balance run a few days ahead of time. But the ExpoDisc is a pretty good suggestion to, as that completely covers the lens to set white according to the light coming from the disc.

Good luck!
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Old August 20th, 2011, 01:00 AM   #3
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Re: White Balancing for inactinic (yellow) light.

If it's a sodium light you won't be able to white balance it, since as mentioned it's a spike and doesn't have a full frequency.

Some light sources you can't white balance completely, so you try to go the the best looking colour effect. You could try doing a normal white balance on their lights to see what it looks like or just leave the camera at the fixed 3200K balance and go with the colour effect. Being a technical area you can get away with a lot and if it was a drama or even a documentary they might try to recreate that safe light effect with their own lighting.

If you've got control you could light your foreground, but if it's a working lab you probably won't be able to..I used to shoot commercials for a supermarket company that used sodium lights in their stores and they never looked great because of the in house lighting. We matched the foreground lights colour temp with CTO, so at least there was more or less a full spectrum on the talent and this was white balanced, but it never really worked that well.

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