I am trying to implement a high resolution modelling application and the models have around 130,000 polygons. There are no textures because of this - there are just coloured vertices. Now, my ambient brightness is up at max but my model is still way too dark. I have tried altering the material properties but nowt works. Is there something special I need to do for high res models?
Nothing special. The full lighting and rasterization rules are specified in the OpenGL specification, which you can download from the front page of this site (right-side column).
Note that both light and material ambient terms are multiplied (and the scene ambient is added) to yield the ambient term. Also, when you use vertex colors, the only way to get that to work with lighting is to use ColorMaterial.