Flash ratings and watts??

[Si Micklewright]

Hi all,

Just wondering here, i was looking at mono block flash heads for studio work and they allways seem to be rated in watts. I have a nikon sb600 speedlight that only gives a guide number on the spec sheet, does anyone know what the sb600 would be in Watts? Ive searched about but cant find anything, am i barking up the wrong tree?

Thanks
Si

 

[Si Micklewright]

The reason i ask is if my sb600 or an sb800 is equivelant to say 200w/s then ill get one of them instead of a monoblock. Cheaper more portable and no wires?!?!

 

[Kentman]

OK I do not know if this will relate to what you are asking but, watts are a product of voltage times amps, this is ohms law and is proven. No good me explaining anymore because I am a reasonable sparks but a c*** photographer. Regards Jim

 

[dazzajl]

You'll probably do better trying to find out the guide number for studio heads to give you a decent comparison.

For the most part (unless comparing the biggest hot shoe units to the smallest studio heads) the studio head is always going to give you more light. Not only that but the recharge time will be far far smaller. This is a really important factor in chosing which way to go as the wait for hot shoe units to recharge during a shoot is so frustrating. It can also really rob the session of any flow as the wait between shots feels almost endless.

 

[StewartR]

I'm not a lighting/flash expert, Si, but I'm a bit puzzled about your question.

Watts are a measure of how much power is put out per second. One watt is one joule per second. So it doesn't make sense to talk about 200 w/s.

As I'm sure you know, the duration of a flash is very short indeed. For the Canon 580EX on a low power setting it can be as short as 1/30,000th of a second. (See here.) So the number of watts that a flash puts out might be surprisingly high, but the number of joules it puts out wouldn't be. And it's the joules that determine the exposure, not the watts.

I agree with dazza that it probably makes more sense to compare guide numbers.