Dielectric trasmittance: some question

Hi guys, I've some question with panel of trasmittance: can I convert the value of physical object to the value of absorption? An example: the persplex (PMMA) has a 92% of trasmittance, how to set the absorption? And in second row: what it means the "Abbe" unit? How can I relate to real physic properties?
This is my preview rendering of Colombo 281 lamp, but I don't know if the persplex material is correct. The caustics is beautiful, but real or not?

Is this a light which iluminates with Optical Fiber? The zone I've marked is due to the curvature of the optical fiber?

To the other questions I can't help you...I don't have time enough to investigate this aspect of Fryrender...But indeed, it's a great caustic effect...Like in the real world!

Thanks for trying Fryrender!

This is a glass with the properties of persplex (IOR, color, etc.). The effect that you have marked is generated by a circular light of 6W (with specific of real Colombo's light for dimension and characteristics) at start of curvature: through glass we see the rear caustics on the floor. The front caustics instead is a diffuse light by material.
Where I read about my question, if you know?

Thanks for your appreciate.