Hi,

I guess your primary source of the heat is from the lamp and its psu. Normally, a 10W tungston (for visible
spectrum) is used in blood chemistry analysers. I don't know what is in your case. Assuming a 10W lamp,
you need about 1.7A of current pass through your 7806.
If input / output voltage differential is high, there will be lot of heat produced from 7806. This will add upto the heat generated by the lamp and the amount of heat will depend on your mounting technics and the type
of regulator package (I would choose TO3) you have choosen. Common practice is to have separate windings for lamp supply and electronics, with minimul voltage differential for the respective circuits they are feeding.

I can understand the reason for using a linear reg for the lamp psu. But, can you consider using a smps for the lamp supply (of course with appropriate specs that matches that of linear reg). And take care of the switching noise at the sensing circuit as your frequency response requirement will allow that.

In any case, in my opinion you might a stiil need a fan to extract the heat from the lamp.