Correct CTB Gels For Day & Night Correction

K

Kevin McCallister

Well-known member
Hey Guys,

I know that the color temperature of the sun varies during the day depending on what time of day it is, but I'm not sure if it gets hotter or cooler as the day goes on. Also, I know the color temperature of an overcast day is different than that of a sunny day. Along those lines, night is a completely different color temperature of moonlight altogether.

That said, I would like any recommendations you guys have as to the exact strength of CTB Gel (1/8, 1/4, 1/2, or full) to accurately balance a tungsten light to these conditions:

1. Sunny - Mid-Day
2. Sunny - Late Day
3. Overcast
4. Nighttime (Moonlight)

What grade of CTB have you found looks best, or produces a great and accurate look of daylight? Also, would you recommend diffusing lights used for day/night light simulation, or is hard light best? Thanks in advance for all your help.
 
According to the professional lighting handbook
Sunset 2300
Sunrise 2500
Moonlight 5400
Daylight 6500

According to rosco gels
full CTB converts 3200 to daylight (doesn't say the temp)
3/4 CTB Converts 3200 to 4700 or daylight below 5000 to bring it to a full daylight
1/2 CTB converts 3200 to 4100
1/3 CTB converts 3200 to 3800
1/4 CTB converts 3200 to 3500

Hope that helps
 
The type of CTB you use depends greatly on the color temperature of the lights you are planning to shoot with. HMI lighting can typically achieve 5600k with only 1/4 or 1/8, but Tungsten lights can take anywhere from 1/2-Full. Most tungsten practicals require full blue to reach 5600k because they are actually 3000k instead of 3200k.
Overcast days are higher color temperature than sunny days, because skylight is very blue. Thusly, when the sun is not as much of a factor, you may need to blue your HMIs up a bit more to stay consistant.
It is typically the most realistic to diffuse moonlight with Opal or 216 diffusion because moon light is a bounced source ~~> Sunlight bouncing off of the moon, which is the biggest showcard of all :)
Hopefully this helps,
 
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