Fresnel texture

[wasd]

From LuxCoreRender manual on Metal material:

Fresnel NK files with measured data can be used as well in either the Sopra or Luxpop formats.

What exactly is those Sopra and Luxpop formats?

[wasd]

SOPRA Database format
Posted on September 10, 2009 by kurniawano
This is the format of SOPRA database provided by FreeSnell manual.
The first number indicates the spectral unit (1 = eV, 2 = um, 3= 1/cm, 4 = nm). The second and the third numbers indicate the spectral range and the fourth one the number of intervals. The N and K values are then stored in the order N,K,N,K…; each value may be followed by a semicolon, whitespace, or both.

Example:

1 .6 6.6 120
1.064 14.4
.987875 13.155
.844 12.2
.672625 11.445
.514 10.8
.438563 10.11437
.396 9.48
this means that the unit is eV (first number is 1), from 0.6 eV to 6.6 eV with 120 number of data points. The next line onwards gives the value of n and k.

If this is right, then I don't get one thing: lux says 'unparseable line 198 blabla' when last line is empty. Why would you even read there, Lux? You were told how many lines you will have, just stop already
I didn't check what if this line beyond limit is not empty, I just removed empty line and lux happily stopped reading data without error.