A spike would only be seen in a real time report of electricity usage. When you turn on an old magnetic one and if you were monitoring it, it would spike up really high for like a split second, then come back down to 600 watts. A digital one won't do that. But it won't really be any cheaper. Maybe the ballast itself runs more efficiently, but it is still using 600 watts to power the light bulb. The amount that it is more efficient might add up to a dollar or two savings each month, if ur lucky.