We have a daytime shoot this weekend with very large windows. I want to switch out the fluorescent tubes already in the ceiling with daylight balanced tubes. There is no time (or money) to get real daylight balanced tubes, and anyway they're eight foot, so they would probably be hard to find. I went down to Home Depot and my options are apparently 5000K or 6500K (Philips). Which one is the lesser of two evils? We are supplementing the lighting with Kino Flows and fresnels with CTB gels.

Also, each bank of lights has a pair of lamps in it. Do I have to replace both, or can I just put one tube in there?

I have seen screw on filters that are supposed to make flourescent lights into daylight. Anybody know if these work like advertised?

You mean a camera filter? The problem here is I need to match the light coming through the windows with what's in the ceiling. I've heard of gel sleeves you can slip the tubes through, but they are expensive and it would seem like they would cut a lot of the light down.

The filters are made by Tiffen- http://www.tiffen.com/displayproduct.html?tablename=filters&itemnum=52FLD

I'm thinking this- if it works- would neutralise the flourescents, and you would have daylight value light.

5000 is closer to sunlight, 6500 is closer to skylight.

Ideally, these bulbs would have a color rendition index (CRI) of over 80, which is a measurement of how even the light is through the color spectrum. But if you're front-lighting with the kinos, this might not be much of an issue, just keep an eye on color, and consider using the overheads mostly for back light as you set up your shots.

But I'd try to get CRI on each bulb before choosing.

Keith, as Marco said, he can't balance the camera to the lights, because he has mixed lighting. Instead, he must balance the lights to the camera. It is difficult to advise which of the two tubes you should get without knowing what the actual color temperature of the day light is. The best thing to do is to take a reading with a color meter. Since the windows are large, it seems your only option is to gel the tubes. If they are going to be visible, it should be okay for them to have a slightly different color temperature, in which case you merely need to remove the green spike with a "minusgreen" gel. If you really want the lighting to be transparent, you might need to combine a CTO/CTB with a minusgreen. Of course, you might not need anything at all if the tubes are good and the natural light matches, so do a test. The part that gets me is that you say you want to use your Kino tubes and fresnels, too. That means two different fluos, a hotlights, and natural light! A real hodgepodge. In that case, I would pick the tube that matches whatever color temperature you have Kinos and fresnel adjusted to. Another realistic option is not to use so many types of lights! Did you calculate how much you need?

Well, not sure how much the fresnels will get used, but I want to keep them handy. The Kino Flows are there to help keep it from getting too flat. To add to my stress, one of the actors is black and the other is white. That's one of the reasons I wanted to have the fresnels, in case I need to throw more light on the black actor. I was thinking about bouncing it on him from the side. I was also hoping to keep it bright enough in there that maybe the windows wouldn't blow out so much. I'm not really sure how to go about calculating the wattages in advance to tell you the truth.

This sounds like the kind of stuff you want sorted out before production. Get a light meter, and bring your camera. If you are not good at using a meter, at least use the camera to tell you roughly how much light you need. Do a test!

If you need to have proper exposure of the environment beyond the windows, this is a difficult task. The likely solutions are to gel down the windows with neutral density gel and to use mirror reflectors to shoot light in the unused windows onto a white card/scrim. Without very bright lights, you will struggle to get decent exposure. I lit a scene of about 10 dancers in front of two bays of double french doors with the ocean in the background. We used ND 1.2 (4 f-stop) gels on the windows and a 42" mirror reflector outside shooting into a white sheet inside. This worked well except for two factors. You must use a frame to clamp fabric tight. Air movement will change your light too much unless you can keep things really still inside. Your crew and actors won't care for lack of air movement during the summer with hot lights. Also, in our case, the sun does not always shine on a reflector and the background simultaneously. If your background is just the nearby area, you shouldn't have a problem since a little cloud will still cover a typical home's property.