I sat down and spoke with Pat at NAB earlier this year. He was of the opinion that most DP's put gels over their lights to modify the color so why make the light absolute color accurate? In a certain sense, he has a point, ...
IMO he doesn’t. What Pat is conveniently glossing over is that no LED (remote phosphor included) will produce the same repeatable result that you get from gelling a continuous source (tungsten) because their spectral output is discontinuous - consisting of peaks and valleys.
What he is failing to appreciate is that all gels (party, effects and color correction) are a part of a finely calibrated imaging system that involves a highly specific light receptor (film emulsion or video sensor), light sources, and color correction or effects gels calibrated for both. Where that exists between film emulsions/video sensors and tungsten and/or daylight sources it is possible to mix dyes in a gelatin materials to create desired effects (it has taken decades to hone this system.) To use the available gels (listed above) on the discontinuous spectrum of LEDs is a misapplication of a finely tuned system designed for continuous spectrum light sources only.
This is true of even the best color rendering LEDs out there (and Litepanels are not among them.) While there is no green spike in the output of a Cineo Trucolor 3200 (as there is in the Litepanels), as you can see from the spectral distribution graph above for the Cineo Trucolor 3200 (black line), there exists a definite green/cyan bump, as well as a spike in the blue range that does not exist in the continuous spectrum of a tungsten light source (green line.) The greater proportion of blue and green/cyan in the Cineo Trucolor 3200 will result in an unexpected and undesirable result if a color correction (CTO, CTS, CTB), or color effect gel (Congo Blue, Bastard Amber, etc.) calibrated for the continuous spectrum of tungsten light is used on this discontinuous spectrum.
The same is true of the Cineo Trucolor with the 5600K panel above. The quite prominent blue spike (black line) will likewise result in an unexpected and undesirable result if a color correction, or color effect, gel calibrated for the continuous spectrum of a continuous daylight source is used on the discontinuous spectrum of a 5500K remote phosphor LED.
Someday, Rosco, Lee, or Gam, will come up with gels calibrated for LEDs but I doubt it will be any time soon given that there is no standard spectral output to LEDs. Perhaps, in the future, when LED technology has become standardized, a system of calibrated gels will be developed; but for now no such color system exists as it does for tungsten sources. Where there are no gels calibrated to correct the discontinuous spectrum of LEDs (remote phosphor included), and the existing color correction gels have undesirable consequences when used on LEDs, the ability to color-correct LEDs is very limited (see camera test results demonstrating this with a Lightpanel 1x1 Daylight Spot.)
Hal Smith summed it up very eloquently in a post on the CML when he said: “… If I light with tungsten, I know what the result is going to look like …. Yes, they're hot; yes, they're bulky; yes, they draw a “poop pot” full of electricity but dammit...I know what the result is going to look like...and don't have to give some post pro a bagful of money to straighten out what the LED's screwed up.”
Guy Holt, Gaffer, ScreenLight & Grip, Lighting & Grip Equipment Rental and Sales in Boston.