I'm planning to change my lighting setup from fluorescent lamps to flash, after the guidance given in this question.
At the moment, my two fluorescent lamps are in a softbox which point away from the subject (still life). The light therefore bounces around my office come studio (approx 4m x 3m), which is conveniently painted white to avoid colour cast, and provides a gentle even light onto the subject. I have fitted roller blinds to the window so that most of the natural light is blocked out and doesn't affect the shoot.
There are two of these lamps both rated at 35W, which according to the manufacturer is equivalent to 150W incandescent lamps. With these, I'm shooting at about 1/8 sec at f/5.6 and ISO 200.
My plan is to buy two flash/strobes to replace both lamps.
What size flash/strobe do I need to purchase to be able to light my subject with an aperture of f5.6? I still plan to fit them in a softbox and fire them away from my subject to keep that soft illumination.
Do I purchase a couple of speedlight equivalents with a GN of 50 to 60 or do I buy some studio flash kits? That causes more confusion as they are rated in Watts. Does Watts translate to GN somehow, for comparison purposes?
My concern is that if I buy the incorrect power, I'll either end up with too much and have to shoot at ISO 100 at F/22 or not enough power even at F/5.6 and ISO 12000.
The flashes I've looked at so far all have variable power, but the range doesn't seem that wide. Should that be a worry?
Of course, if my plan is all wrong, please feel free to correct my before I waste my hard earned cash on the wrong kit.