Is the angle of the spotLight measured in degrees or what?
What's the meaning of the exponents?
Thank you very much. 
I've updated the javadoc for angle and exponent to better explain. Here are the relevant sections:
* <code>setAngle</code> sets the angle of focus of the spot light
* measured from the direction vector. Think of this as the angle of a cone.
* Therefore, if you specify 10 degrees, you will get a 20 degree cone (10
* degrees off either side of the direction vector.) 180 degrees means
* radiate in all directions.
*
* @param angle
* the angle (in degrees)
* <code>setExponent</code> sets the spot exponent of this light. This
* value represents how focused the light beam is.
*
* @param exponent
* the spot exponent of this light. Should be between 0-128
Thank you renanse:
very clear and very useful!