Dear Abhishek,

I assume the new lamp setup fulfils your light output requirements. Personally, I am skeptical about operating the lamp at half its operating voltage and getting a useful output from the lamp. But, I may be wrong.

Your circuit proposal will definitely work and temperature variations will not be a major issue as your calculations are based on relative measurements (between blank, standards and sample). You can look into the possibility of using trimpot instead of fixed resistor, so that you can optimise (and/or calibrate) the circuit operation for the frequency (wavelength?) of interest. Alternatively, you can consider a DAC + LM317 or DAC + buffer combination, which will give a better and versatile control over the operation. I can suggest AD5300/5301 which is cheaper and has serial comm. You can also use other cheaper varieties.