Hmmm. The idea of adding a specular light to add sheen is interesting. I've been trying to get a similar effect by adding various specular nodes in the shader.

I'm trying to make a hair shader that will deliver decent results in all possible lighting situations. Just as you did, I experimented with ambient and translucence, and found these could deliver dramatic effects, but a small change in the lighting would then produce strange and unpredictable results.

But an additional light on the hair is more akin to what would be done when filming in the real world, this may help me find the general case solution that I'm looking for.

Thanks!