The defaults when a light is created is pure white diffuse light, with no attenuation (does not decrease with distance) and a range of 1000 world units.
Lights are created by using the SceneManager.CreateLight method. They can subsequently be added to a SceneNode if required to allow them to move relative to a node in the scene. A light attached to a SceneNode is assumed to have a base position of (0,0,0) and a direction of (0,0,1) before modification by the SceneNode's own orientation. If note attached to a SceneNode, the light's position and direction is as set using Position and Direction.
Remember also that dynamic lights rely on modifying the color of vertices based on the position of the light compared to an object's vertex normals. Dynamic lighting will only look good if the object being lit has a fair level of tesselation and the normals are properly set. This is particularly true for the spotlight which will only look right on highly tessellated models.