if you're asking about 'digital' and 'magnetic' ballasts, the difference is about a hundred bucks ... just kidding ... the old magnetic ballasts are rugged, reliable, and withstand electrical fluctuations well ... the newer digital ballasts are more efficient, and use a bit less electricity, while putting out a slight amount of additional light, supposedly ... but, they are also more sensitive to electrical fluctuations, and can fry easier ... personally, I choose reliability over efficiency, in the matter of ballasts ... :smokin: