There are several reasons for power loss in a laser, but most of the losses are from Fresnel reflection of the laser beam off of the two (2) surfaces of the lens or window and from absorbance. Power loss in a laser system is a function of reflection losses and absorbance. As noted above, all of the materials used for Lens Savers® windows absorb very little energy. Accordingly, substantially all of the losses users experience are from reflection until the window becomes damaged by spatter. Reflection is a function of the refractive index of the optical material. Those losses are described above in the section on reflection and absorbance.

In practice, power loss translates into slower operation of the laser, except at the margins where power loss will be so severe that cutting of particularly thick material becomes impossible.