I’ll start by saying that the color spectrum of the back-light is important. To make an extreme analogy, you could eliminate the back-light altogether and capture using a night vision camera, but obviously the results would be terrible. So to a lesser extent, that is the case when we rely on electronics to make corrections. Begin with an image that is projected in a form that is as close to the desired result as possible, then “tweak” it via electronic means if necessary, but the goal should be to minimize the amount of post processing, and I would even include the color balance feature on your camera as a form of “post processing”. Some amount of post processing may be desirable (e.g. to clean up or even sharpen a dull image), though when you do that, you want to provide as much original information as possible from the native image.
So the first problem is that “white” LEDs typically have a very skewed color spectrum (see image below), for example, blue tends to be over represented and red tends to be under represented. Have you ever taken a dark image and tried to lighten it via image processing software and noticed that the result now looks grainy? The reason for that is that you can’t electronically add back missing information. So if a particular set of colors are under represented in intensity, then electronic compensation can only work with the available information. It will do its best to compensate, but it can’t add back missing information.
To even begin to compensate for a “white” LED using your camera’s color balance means that you would have to project a known white source (e.g. a white piece of vellum) to your lens using the unbalanced LED and calibrate your camera’s white balance based on that. At that point you are making the assumption that your camera’s white balance completely negates the affect of your off spectrum “white” LED source (i.e. “flattens” the curve in the attached diagram).
There’s also something called “scene by scene” color correction. High end scanning services provide this as an option. It means that the color balance can change from one scene to the next based on a variety of conditions such as the original lighting, original movie camera settings, and film degradation (e.g. the red “vinegar” aging that some 16mm films have). Since it is nearly impossible to know what the original color balance for the particular scene was, the operator must make a subjective determination of what it should look like. This is where having distinct RGB channels can be utilized by the operator to find the most natural and pleasing color balance for the given scene.
I’ll add that when considering a back-light design, considerations such as providing effective diffusion and an appropriate means of dimming are important. If PWM is used, it may cause an interference pattern with some cameras, so in that case, it’s best to rely on analog means rather than digital means to control intensity.
Having said all that, if you’re willing to forego the ability of scene by scene correction, it may be sufficient for your needs to use a “white” LED (better, as I stated above, if your white balance is calibrated to the LED). Ultimately, like anything else, it all depends on whether or not you are happy with the end result.
