Radiation reaching the joint surface can be reflected, transmitted, or absorbed. Reflected radiation hits the part surface and bounces off, while transmitted radiation travels through the part unaffected. Reflection from all plastics is low (5-10%). Laser radiation can be absorbed at the surface of the material or can penetrate to various depths depending on the wavelength of the incident beam and the amount and type of pigment, filler, or reinforcing additives in the plastic material. Absorption results in heat generation within the plastic. The spatial distribution of the heat is described by the Bouger Lambert law of absorption: