Since RGB does not preserve spectral information, POV-Ray naturally has 
to guess how a colored light might disperse.  I got curious as to how 
POV-Ray's dispersion of black body emissions would differ from a 
spectral render.

These scenes show a glowing rod viewed through a BK7 glass filter. 
Image prism_whites-rgb.png is the native dispersion render, and 
prism_whites-spectral.png is the spectral render.  The geometry of both 
scenes is identical.

The RGB render shows less refraction than spectral render, so I 
#debugged some values.

IOR_Glass_BK7 from spectral_glasses.inc:
   IOR at 380 nm = 1.533745 (SpectralRender shortest)
   IOR at 580 nm = 1.517122 (near Fraunhofer line D)
   IOR at 730 nm = 1.512304 (SpectralRender shortest)

Native dispersion from ior.inc:
   iorCrownGlassBK7 = 1.516730 (presumably at line D, 589.29 nm)
   dispCrownGlassBK7 = 1.010552

What surprised me is that POV-Ray's native dispersion changes the hue of 
each spectral color.  For example, the violet extreme is ultraviolet 
blue for the high temperature white, and reddish purple for the low 
temperature white.  (It's still a whole lot better than POV-Ray 3.6 
dispersion.)  The spectral render merely adjusts the intensity of each 
band without changing its hue, as expected.

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Download 'prism_whites-rgb.png' (32 KB) Download 'prism_whites-spectral.png' (35 KB)

Preview of image 'prism_whites-rgb.png'

Preview of image 'prism_whites-spectral.png'