[Greg McKaskle]

HSL is a 3D color space as is RGB. RGB are generally viewed as a cube with a red, a blue, and a green axis. That puts black in the 0,0,0 corner and white in the 255,255,255 corner.

HSL has one circular component and two linear components, so it is pretty naturally thought of as a cylinder. But, the issue is that not all of those HSL values are really unique. If L is zero, the color is black, it doesn't matter what hue is, and saturation means nothing if there is nothing to blend with but black. So another visual that is more compact is to think of it as a snow cone with another paper cone put on top. This is really just taking all of the similar colors and shrinking them inwards so that the cylinder has been deformed to have a peaked top and bottom.

Anyway, when L is at an extreme, the other values really don't matter. Thus white light can have any hue, is by definition going to have a very low saturation, and will have an L that is almost 255. So, it is possible to use HSL to threshold, but since you really only care about L, it is generally faster and clearer to extract the L plane and do a monochrome threshold. It is even faster to ask the camera to simply give you a monochrome image, and you may have luck with that.

As for whether this is better than a green light, I'd say that it isn't better, but it may be good enough. If you have the time, I'd encourage you to experiment with both.

Greg McKaskle