Recently I have been experimenting a lot with mixing different light sources weather it’s studio flashes, System flashes or constant lighting. And guessing the exposure can get complicated. Guide numbers are mostly used on system flashes (speedlights) and watts-second is being used on monolights.
Watt-seconds (Ws) is a unit of energy. When reading flash unit specifications, the Ws rating is the amount of energy that can be stored in its capacitors and released when the flash is fired.
The Guide Number (GN), on the other hand, is a measure of light. It indicates how intense the light from a single flash is when falling on the subject.
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