Black Body Colour/Brightness Nodes (cycles)

Description:

Edit: I have added an animation showing this node group in action. The only parameter changed during this animation is the input temperature.

https://www.youtube.com/watch?v=d7XK31Vmg7E&feature=youtu.be

Cycles already includes a black body node to convert temperature into colour (hotter temperatures are less red and more blue) - however in the real world, the brightness of an object also increases with its temperature (the the 4th power) according to Plancks law. My node setup also goes to a higher (bluer) temperature than the unbuilt node which is limited to 12,000K.

This node setup uses a colour ramp to convert temperature to colour according to the conversions given here:

http://www.vendian.org/mncharity/dir3/blackbody/UnstableURLs/bbr_color.html

It also contains a factor to increase the brightness with temperature. The node group has the following inputs:

Temperature = Temperature in Kelvin (between about 700K and 40,000K). Every day lights have a colour temperature around 2500K.

Exponent = Controls the rate at which the brightness increases with temperature. To by physically accurate its defulted to 4 (doubling the temperature increases the brightness by 4 times). Lower values will make the brightness ramp up slower (e.g. 2 will double the brightness as the temperature doubles)

Cutoff temperature = this is a lower bound to the temperature below which no emission will occur.

Brightness = Controls the overall emission brightness (Lower values = dimmer)