I'm just in the process of adding some extra hardware lights to my pinball sim for the flashers.. I'm just using positioned lights and want to limit how far it shines so to speak so it brightly lights the area around it and tapers off. at the moment its lighting the entire playfield which is what I don't want.. many thanks in advanced..

it depends upon what kind of lightning you are using. if it's ambient then there is no way to limit the distance.

one of the light type is Spot Light. It's the heaviest, but it's unlikely to have a significant impact provided the modern day GPUs.

With Spot Lights, not only do you get the capability of limiting distances, you also get the capability of defining an umbra and penumbra... you can find a lot of material on this type of light on the net and even in the DirectX SDK. Happy hunting :-)

You are looking for light attenuation. This is when light intesitiy changes based on distance from light. The whole process is described in chapter about lighting in OpenGL RedBook (free in PDF & HTML).

And when you attenuate lighting, you mught also want to simply disable lighting when the object is too far to be lighted. It will save some GPU computations.