That would make some kind of sense to my very mechanical understanding of things electrical, Ken.
I expect a minimum voltage is needed to turn the lamp on, after that the extra energy must go somewhere... sure the intensity will go up, but maybe the peak intensity will shift like the temperature changes in stellar spectra (I'm not saying we achieve stellar temps
). The only other mechanism I could think of for the variance would be resonance in the lamp
... some frequencies reinforce, while others cancel...
...but I'm only guessing...
Al.