vector blackbody(float temperature, float luminance)
Given a temperature, in Kelvin, and a luminance value, computes the color of an incandescent black body as CIE XYZ tristimulus values.
The computation uses a fast approximation, which is valid for temperature values between 1666K and 25000K. Values outside of this range are clamped to the nearest valid in-range value.
The returned value can be converted to linear sRGB values using the xyztorgb function.