W/S and GN

[ffscj3562130]

I understand (or at least I think I do) that the GN is more important than the w/s produced by a strobe. My question is what causes two different strobes of the same w/s to have different GN values?

[OsmosisStudios]

Studio strobes are generally measured in W/S, onboard and hotshoe flashes are usually measured in GN.

[ffscj3562130]

I'm looking at beginner studio strobes to try and learn that aspect of photography. On this forum it was explained to me that you needed to use the GN to help in determining the aperture for using studio lighting so I started looking at the GN on various beginner strobe kits and have seen that even though the w/s were the same the GN was different. I was just wondering why.

[OsmosisStudios]

W/S (watts per second) is the amount of power used, GN is the amount of light being provided.

[Benji]

Once you place any kind of a light modifier in front of any light source you immediately alter the amount of light reaching the subject, and the amount of light reaching the subject is what is important, not the original amount of light put out by the oroginal source. Of course the higher the W/S or G/N the more light will be pumped through the modifier and onto the subject.

Benji

[zona5101]

The w/s is a measure of stored energy. How much of that energy is converted into light is where some flashes differ. That is why many look to the guide number because it is a measure of light output...in photographic terms. A guide number is measured at a stated iso @ 10 feet. For example a GN of 110 at iso 100 means at full output your fstop will be f11 at 10 feet
(110/10).
From there you can think about light modifiers and say a soft box will eat 2 stops of light then you know your max aperture for the exposure will be f5.6
You can't determine that kind of information from w/s.

[ffscj3562130]

Thanks all for your answers. Zona, I understood about the GN at 10' and the aperture. But you answered my question in that it how each brand converts that energy into light that causes the difference.

Thanks again all.