i found a kit with 6 varying shades of blue gels for converting incandescent/tungsten lights to match daylight.

my question is: how does one know which gel or combination of gels to use? do you just "eyeball" it?
is there a technique for determining how to match the outdoor light? some kind of color temperature meter??

thanks

bobby

I've found some info. the Lee filter kit contains 6 shades of gel -

200 Double C.T. Blue
Converts tungsten (3200K) to daylight (26000K)

201 Full C.T. Blue
Converts tungsten (3200K) to photographic daylight (5700K)

202 Half C.T. Blue
Converts tungsten (3200K) to daylight (4300K)
.
203 Quarter C.T. Blue
Converts tungsten (3200K) to daylight (3600K)

720 Durham Daylight Frost
Smoothes PAR or flood washes of large areas. Useful for houselight and good for entrances from natural light.

218 Eighth C.T. Blue
Converts tungsten (3200K) to daylight (3400K)

also, found this rough estimation of outdoor color temperatures:

.

Light Source.........................Kelvin temperature......................R G B Values

Candle......................................1900.......................................255, 147, 41

40W Tungsten.......................... 2600.......................................255, 197, 143

100W Tungsten.........................2850.......................................255, 214, 170

Halogen...................................3200.......................................255, 241, 224

Carbon Arc...............................5200.......................................255, 250, 244

High Noon Sun..........................5400.......................................255, 255, 251

Direct Sunlight..........................6000.......................................255, 255, 255

Overcast Sky............................7000.......................................201, 226, 255

Clear Blue Sky..........................20000.......................................64, 156, 255

Plus, there are color temperature meters, but they're $1,500 +

Thanks I love the Lee Daylight Filters, now I actually know which ones to use, up until now I've been eyeballing them.

i found a kit with 6 varying shades of blue gels for converting incandescent/tungsten lights to match daylight.

my question is: how does one know which gel or combination of gels to use? do you just "eyeball" it?
is there a technique for determining how to match the outdoor light? some kind of color temperature meter??
thanks bobby

There are color meters that will read the color temperature or red/blue balance of a light source that you can use to calculate which CTB Gel to use. The easiest thing is to take a color reading of the source you want to match to and then hold the CTB gels one at a time over the meter sensor while reading your tungsten source until you find one that matches the source you want to match to. Color meters will also measure the green/magenta balance so that you can match that axis to the other source as well. There is one exception though color meters don't read LEDs accurately because of their discontinuous spectral out put.

You should also know that tungsten light is so deficient in the blue part of the spectrum that it takes a quite saturated blue gel to balance it to daylight. In fact, the transmission coefficient of some Full CTB gels is only 24%, which means that it passes only 24% of the source. Which makes gelling tungsten lights is a very inefficient way of creating a daylight source (a tungsten 1000w gelled with CTB becomes a 240W daylight source.)

- Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental & Sales in Boston

Does anyone know how these filters combine?
for instance, if one filter converts tungsten to 4600k -- and another converts tungsten to 3400k - will the two together convert to 10,000k? (just adding the values together?)

I suggest you get this book it will explain a lot more than can be said on these forums and give you a good basics in lighting technique: Motion Picture and Video Lighting : Blain Brown : 9780240807638 (http://www.bookdepository.co.uk/Motion-Picture-Video-Lighting-Blain-Brown/9780240807638)

thanks for the suggestion. I just found the book you mentioned at the library.