Wyatt Garfield

Agree 100%. However, skin seems to be particularly revealing of spectral deficiencies. This is due in part to the fact that we know how healthy skin should appear, but it also has a lot to do with the complex quality of skin. Polluted skin tones cause a lot of strife on set and in post, and I think it's helpful to recognize that a subject's face contains many tones (specular highlights, lips, skin, creases, bloodvessels, etc), all of which react differently to spectral deficiencies. With each tone reacting differently, the natural relationship between them is lost, causing an unnatural appearance. While solid opaque colors (like the chips on a macbeth chart) can be easily keyed and corrected in post, the complex detail of skin is nearly impossible to make true in post. As for my vague reference to "color dimmable LEDS", I was thinking of units like the Arri LoCaster, which I have not used. I would love to hear if anyone has done any spectral analysis of those units. Also, I would imagine you're completely right about RGB LED clusters being a complete disaster for color rendition. Interesting to think about spikes passing the CRI test swatches, only to hit a monochromatic surface in practical application... I didn't realize that's how the CRI rating system worked. The more I learn about the CRI system, the less I like it! I'll only refer to it only when discussing it's shortcomings from here on out.

Great post, Guy. I think what many people don't realize is that human skin is not a solid color, so gelling lights cannot make up for spectral spikes/gaps. Imagine you have an LED source that appears to output pure 5600K, but is in fact a discontinuous spectrum of wavelengths which are mixed to appear white. When you shine this light on a subject, a percentage of the light is reflected off the immediate surface of their skin, sending back specular highlights which are uncolored by the skin, and which read on camera as neutral. The remainder of the light passes into the many translucent layers of the epidermis, where various wavelengths are scattered, absorbed, or reflected back. This is where the trouble begins (as well as some conjecture on my part). The pigment in their skin cells may absorb some of the spectrum but reflect a green spike, while their skin pores, blood vessels, and creases may absorb the green spike but reflect a red spike with a vengeance. If any combination of these phenomenon is occurring, you get strange skin tones mottled with pink and green or other colors (hence the zombie effect). You can try to compensate with gels, but the relationship between the various colors in the skin has been shattered. If you add plus or minus green, you tint the highlights, potentially accentuating the difference between the highlights and absorbed skin tone. If you're in a bind, makeup can help unify the mottled skin tones, and diffusing sources to soften the specular highlights can help (again helping to unify the discrepancy between highlights and skin tones). Also, I've learned to avoid gelling daylight LEDs to tungsten, as that seems to hurt the color rendition dramatically. I read somewhere that color dimmable LEDs have smoother curves because the multiple colored LEDs fill in some of the gaps, but I'm not sure if this is true. The worst LEDs I've used were some "Cool Lights" daylight 10x10s a few years ago, which lead to all these thoughts on how skin responds to uneven light emissions. Litepanels seem better, but still cause some problems (especially when gelled from 5600 to 3200). The color of Daylight Rosco Pads read much different on digital cameras than to the eye, which makes me think their CRI is not good, but I haven't seen anything too strange going on with them. Of course, test any new products before you use them, as these opinions are drawn from experiences with specific applications, and are not universal truths!