will give you the best penetrating power. Most people use actinic suppliments with MH
becasue the bulb spectrum of the lamp is generally 10,000-14,000K. That is a bit more yellow/white looking light with less blue in it. People use actinics to round out the blue portion of the spectrum as it tends to be more pleasing to the eye. You can get by with without actinics if you choose a MH
buld that is 14,000-20,000K. The 20K will appear more blue then the 14K. It is a matter of personal prefernce.