How many watt-seconds?

I'm considering getting a monolight kit. I see that Bowens has a kit with two 200 watt second Gemini monolights. Is this (400w/s total) enough power for small scale studio portrait work? I've been using a pair of Canon 580 flashes with umbrellas and the ST-E2 transmitter but think I'd like to try a monolight system. Also comparing guide numbers of various units seems futile as the numbers are all over the place. Logic would seem that a monolight (with its larger power supply and capacitors) would put out more power than a shoe mount flash. Correct? Thanks.

Yes, 400 ws is enough for small scale studio portrait work. One of the problems with comparing monolights with hotshoe flashes is that the two systems have been measured differently. Hotshoe flashes are measured by their output in the form of guide number. Guide numbers take into account distance and include the impact of the focusing lens on the front of the flash. Studio strobes are compared by their potential output in WS. The studio strobes will be more powerful than your hotshoe flash.

Using two 200 Watt second strobes will give you a lot of flexibility.

Where it may fall short is if you are going to be using large modifiers at greater distances from the subject and still want to shoot at f/8 or f/11. At close range you'll have no problem shooting at anything from reasonably wide apertures to fairly small.

For typical main and fill or any combination of main, fill, hair, background, accent, etc. you'll find that 200 Watt seconds will get you there and back with no trouble.

Thanks for the quick replies and words of encouragement. I will mostly be using a pair of umbrellas (main/fill scenario), but on occasion will switch to one umbrella and one snoot for hair, with a reflector as fill.

Comparing watt/seconds among manufacturers can be confusing too. Watt/seconds is a measure of electrical energy released. Depending on the efficiencies of the design of everything else, it can result in different amounts of light actually produced. It's probably more fair to say that you can compare lights that are offered from a given manufacturer to each other, but it starts getting inaccurate comparing the offerings from one company to the next.

Personally, I'd prefer to get the weakest light that I can live comfortably with. It gives you a lot more flexibility to shoot at wider apertures if you want. Honestly, it's the MINIMUM power that is one of the things I am most concerned with in looking at lights. Because shooting at F/11 or F/16 doesn't make too much of a difference, but being able to shoot at F/2 gives you more creative options.

picturecrazy wrote in post #11294581
Personally, I'd prefer to get the weakest light that I can live comfortably with. It gives you a lot more flexibility to shoot at wider apertures if you want. Honestly, it's the MINIMUM power that is one of the things I am most concerned with in looking at lights. Because shooting at F/11 or F/16 doesn't make too much of a difference, but being able to shoot at F/2 gives you more creative options.

Then these would seem satisfactory based on that. They are adjustable from 200 watt seconds down to just 12 watt seconds. 12 watt seconds when working through an umbrella should allow for some fairly wide apertures.

picturecrazy wrote in post #11294581
Personally, I'd prefer to get the weakest light that I can live comfortably with. It gives you a lot more flexibility to shoot at wider apertures if you want. Honestly, it's the MINIMUM power that is one of the things I am most concerned with in looking at lights. Because shooting at F/11 or F/16 doesn't make too much of a difference, but being able to shoot at F/2 gives you more creative options.

In studio I don't find that too much of an issue but outdoors I do like to use a wide aperture. But ambient lighting is usually too strong so I have to use ND filters so I haven't run into an issue with minimum power being too high. Personally I'd rather have more power and use ND filters but I could imagine scenarios where it wouldn't be feasible.

emitecaps wrote in post #11295311
In studio I don't find that too much of an issue but outdoors I do like to use a wide aperture. But ambient lighting is usually too strong so I have to use ND filters so I haven't run into an issue with minimum power being too high. Personally I'd rather have more power and use ND filters but I could imagine scenarios where it wouldn't be feasible.

Shooting outside and shooting inside are two completely different matters. The OP says it's for small scale studio work, which is most likely indoors. Outdoors, you need light that is as powerful as the ambient light, so yes, you'll need more power. But that isn't as big of an issue indoors.