A nice feature of Vue is the possibility to add dispersion effects for materials with a non-zero refraction index. Dispersion is the result of the fact that the refraction index of a material is dependent on the wavelength of the light.
We all know this effect from a prism where white light is dispersed into rainbow colors, but also the sparkling of diamonds is caused by dispersion.
In real life, what is usually called white light is a continuos spectrum of all wavelengths depending on the properties of the emitter. This is called black body radiation in physics. The perceived color varies with the temperature of the radiation and the properties of the sensor. Bright sunlight appears white to us and corresponds to a temperature of about 5500 K.
Now you might think that the “spectral” atmosphere settings of Vue will reflect the physical properties of sunlight. But if you create a scen with a prism, you will notice that white light (and all other colors) in Vue is treated as a mixture of red, green and blue light, as represented by the RGB values you can set in the options dialog for the light source. So in a way, the “spectral” name for atmosheric effects is a bit misleading.
The type of the light source does not matter for this effect. A spotlight acts the same as the sun or a point light. Thes types only differ in the way shadows are created. The special feature of the sunlight only is that it influences the sky and cloud colors, but the calculations for these effects also rely on the RGB values instead of a black body spectrum.
For most purposes, this “fake dispersion” does not really do any harm, as the spectrum usually is squeezed together so much that the RGB nature of the light can’t be detected. But if you want to do closeup renders of optical effects, you will hit the limit of realism that can be achieved with Vue.
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