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Message: <blockquote data-quote="WayneF" data-source="post: 385962" data-attributes="member: 12496">For portraits, I use a 40 inch (1 meter) Large softbox at arms length (usually 30 inches) with a 160 watt second light turned down to less than 1/4 power, for about f/8 ISO 100.   Each f/stop above that would be double power, ie, f/22 is 3 more stops and 8x more power (than f/8).My space (after I move furniture) is about 10x19x10 feet (sideways in a larger room).   I have a couple of 320 watt second lights, but I very much prefer to use my 160 watt second lights (to avoid turning them down so much).  I use one of the 320 watt seconds in a very huge 5 foot umbrella behind the camera for fill light at ten feet from subject, turned down to 1/8 power.  The other big one is in a grid for background (relatively unimportant there).The problem with excessive power is that sometimes it cannot be turned down far enough to be usable, esp in a small space.Before spending a lot of money, I think a very good plan would be to rent some lights one time, just for the experience of seeing what they actually are.  Local photography clubs often have light sets that can be loaned to members.The relation is not to the size of the light box.  We can put a speedlight (about 75 watt seconds) in a huge softbox or umbrella.  We can bounce a speedlight from a huge wall or ceiling, etc.The power relation is to the subject distance, fstop, and ISO.The "rule of thumb" (for soft light) is that an X size softbox or umbrella can cover a subject area about X size when about X distance from it, and be acceptably soft.1 meter high half torso... 1 meter softbox at 1 meter distance works.2 meter high standing full length, 2 meter softbox at 2 meters works.Again, the power is not about the softbox size, it is about the distance, fstop, and ISO.  But large boxes are used to cover greater areas at greater distances.</blockquote>

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