Light Sources and Color Spectrum. Simply.

October 28, 2013

I want to make this as simple as possible, and it’s a subject that invites you to dive in to all manner of techno-vortices of Color Science.  It’s really a simple question, though.  Does it matter which light source I use to illuminate artwork for reproduction?

I’ve argued that the color and quality of the light source is crucial in reproducing the vision of the artist.  I think I’ve demonstrated pretty well how the light quality affects the texture and surface of the canvas, but I’ve been struggling with a good way to demonstrate how the light color affects the perception of the various tones and values in a painting.  I’ve been tempted to go into a deep, technical discussion of it, but then realized it’s really a very simple thing.  Show how the colors are different with three basic light sources – tungsten, strobe and “full spectrum” fluorescent.  The simplest way to show that is with a Colorchecker.

Basically, think of it in terms of throwing something at an object, and getting what bounces back.  You can’t get back what you didn’t toss in the first place.  If you’re not throwing red, for example (in the case of a fluorescent, specifically), you’re not going to get red bouncing back to the camera.

First, the video:

Now, the details.

The “Tungsten” version was shot using halogen gallery-type floods, the camera set to 3700K, and shooting RAW with the Nikon D800.

The “Strobe” version was simply changed to 5000K, and the “Fluorescent” version was 5000K as well.  The fluorescent bulbs are so-called “continuous spectrum” 5000K bulbs, which is really a misnomer, a fact you can see by simply looking at a spectral response graph of any good bulb of this type, including those used on the Cruse Scanner and other similar devices.

The files were processed using Adobe Camera RAW, and a click-gray balance was made on the lighter of the two center gray patches.  The shadows and highlights were adjusted slightly so the shadow and highlight points on the histograms would match up well.  The files were cropped to the target, and processed with the default Adobe camera profile.  The Working Color Space is Adobe1998.

Remember.  The primary objective of the entire science and technology of CCD development and Color Management is to replicate the human visual experience of color.  Color management tools’ job is to take these colors we see above and try to correct them to match the known colorimetric values of the target.  They can do that a lot better and bring the colors closer to what we perceive if they have a starting point closer to where they’re trying to end up.  If they don’t have the colors, they have to make them up, or stretch the colors they do have into the space they need to be.

The conclusions are pretty obvious to the eye, but even more so when you look at the histograms.  Each light source is indeed different.  The intensity of each of the color patches on the Colorchecker is rendered in a slightly different way in some cases, in others, the differences are pronounced.

So, yes, each is different.  That begs a few questions.

Which one is more “accurate”?  That question will send you down another vortex of Color Theory.

Which one is more faithful to what the artist saw?  That question is simple.  The light source that the artist used when creating the work can only be the most faithful to the artist’s vision and intent.


2 Responses to “Light Sources and Color Spectrum. Simply.”

  1. […] For a nice, simple visual demonstration of this, see my post here: Light Sources and Color Spectrum, Simply. […]

  2. […] my previous post I showed the comparison between shots of a Colorchecker lit with three different sources – […]

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