, the system draws just 40 Watts @ 24V, yet outputs the equivalent of 500 Watts
I'd love to know where they get their figures from.
The poorest incandescent lightbulbs - which are flashlight bulbs and indicator lamps, not filmmaking devices - may achieve a luminous efficacy of ten lumens per watt. Better, halogen-technology incandescent lighting of the type you're actually likely to use, makes more like 30. White LEDs of ten times this efficacy do not exist at any CRI. The best current types make perhaps 150 lumens per watt, on an exceptionally good day, and are generally large-die devices of the type found in high performance flashlights or filmmaking equipment such as Outsight's CreamSource, not the 5mm diameter types used by Litepanels.
And this is before we even consider the efficiency of the power supply. An extremely carefully-designed 40W-capable switch mode current regulator might achieve an efficiency exceeding 90%, but there are significant technical challenges involved in the efficient and well-regulated running of such large arrays of LEDs. This is another reason that a smaller number of larger junctions, again like Outsight's products, may be a better bet.
Solid state light can be much more efficient than tungsten and is becoming more efficient than fluorescent, but it is not twelve times more efficient - more like five or six. I invite someone from Litepanels to come and tell us how they've built a lighting device that's twelve and a half times more efficient than competing filmmaking gear, or at least admit that they're comparing it to the efficiency of christmas tree lights.