In order to white balance, you’re seeking fairly homogenous light conditions around your subject. But what if they’re not? Balancing out one problem can frequently aggravate another. You could overwhelm the ambient light with sheer wattage but that would require a lot of weight and equipment. Interviews are all about speed and portability.

Making all of your sources the same color Let’s assume for the moment that you are using tungsten light. Your lights are 3200K, and the room lights are either 2500-3200K, if they’re tungsten. If they’re fluorescent they’re 3500K for warm white, 4500K for cool white or 6500K for daylight balanced.

Kelvin represents just the red-blue spectrum of color temperature. Most fluorescents have a degree of green to contend with: up to 30 points. Throw your window light into the mix and you have three disparate light sources which you can’t white-balance away. A large film production crew would gel the windows and overheads or sleeve the fluorescents to match your lights, but I’m guessing that’s not in your budget, either time-wise or financially.

Plan B is to just turn the overheads off or at least disable the lamps in the immediate area around your set. Then you’ve only got the windows to deal with. Mid- to late-afternoon sun will probably come in close to 3200K, but I’d have some sheets of Rosco 3316 (1/8th blue) or 3208 (1/4 blue) on hand to put on your lights, just in case. For strong blue north window light, pack some 3204 (1/2 blue) or 3202 (full blue) which will raise the color temperatures of your lights from 3200K to 4100K and 5500K respectively, to match the incoming window light. Then you can read for white balance. It’s not written in stone. It just has to look good. Of course, you can eliminate this entire step by shooting at night, or in a windowless area.

I haven’t listed filtration to match the various temperatures of overhead fluorescents because I’d rather exhaust every other possibility first, but you’ll probably be adding #3304 (Rosco "Plus green"; approx. 30 points of green) for 3200K lamps, #3304 + #3204 for 4100K lamps and #3304 + #3202 for 5500K lamps–if you go this route.

It’s a bit confusing, but the concept isn’t: make all your light sources the same color before white balancing. Remember, these gels are added to your light sources to match them to the ambient source.