Every light has an intensity level. If you lower this value, the light will become increasingly dim. This will, however, affect both diffuse and specular properties of each light at the same time. So, what I prefer to do is to go into the material room, and lower the diffuse color value for the light if it's too bright in my scene. For instance, if the diffuse color of your light is pure white, try lowering it to a light grey. This allows the light to maintain nice specular highlights, while reducing it's intensity on the diffuse (color) channels of each material. You can play with the diffuse and specular color/intensity on all the types of lights in P6 independantly through the material room, which provides great control over how they react with materials in the scene.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.