I agree with Phil.
The claimed benefit of the product is that it isn't flash, so the best thing for you to do is to experiment with using it as is, at the very close distances that you'll need to use it at to obtain the soft light claimed for it and to end up with enough usable power, and forget about using flash with it.
But, as Richard pointed out, if you do want to use it in conjunction with flash then you can, you will just need to increase your ISO setting and/or slow down your shutter speed to the point where the Rotolight will give the required exposure, the increased ISO will make even the lowest powered flashgun seem to be very powerful so you will need to turn the flash power down very low.