Color Meter CCi vs CClf Correlation

[Brandon Leger]

I was doing some color testing on lights and noticed something interesting in my readings. I can't seem to find a consistent correlation between the CCi reading and CClf. For instance, at 6000k, the light read CCi: 0.2M and CClf: 1/8 minus green but at 5600k, the light read CCi: 0.1M and CClf: 1/8 plus green. I'm not sure why this jump over the black body radiator curve in gel but not in the correction index. Any explanation for something like this? Anybody know of any deep dives into these measurements? Thanks.

[Ravi Felaffa]

Hey, Brandon...I have some experience with this.  I think you must be using the Sekonic C-700 or 800 color meter.  The CClf function is meant to recommend a color filter to correct the light to your target color temp and to correct any green or magenta shift in the light.

I have balanced hundreds of lights--HMI, Xenon, and other discharge lights to be color corrected for camera, and I can say the light filter recommendations are not accurate at all.  It's a nice feature and perhaps it gets you close, but I would not believe those suggestions.  CCi .2M shows a tiny amount of green in the light, as you know.  And maybe 1/8 Minus Green would correct it to 0.0. And .1M shows even less green in the light, but still technically a little green. So a Plus Green filter would not take the light in the right direction, also as you know.   The overall color temp, 5600 or 6000K isn't the issue you're describing...it's the amount of green or magenta in the light to the point where the camera would detect the added influence of green or magenta.  And if you've added a CTO to a light to take it warmer, 6000 to 5600, the filter itself can usually add more green to the light, but some filters actually have some pink in their formulation and so it messes with the final reading.

That being said, anything is possible and some lights react differently to the meter and to the color filters applied. Some color brands have more pink or green in them, too, as I mentioned.  I always have to adjust by trial and error, for better or worse.   The main takeaway is, don't take those filter recommendations as gospel.  I know this doesn't address the "black body curve", but it does address the practical issue of correcting the light. 🙂  

I'd be very interested to see any others' experience with this since I can only speak about my own experience.