2x580 ex twice the power or more of the same power?

If im setting 2x 580 ex at for ex 1/8 of power will i get a 1/4 of power or will it be the same but with more of the same light?

light power is a measurement of the lumens output relative to the flashes "normal" output. so having two outputting 1/8th of the normal output of lumens would work out to 1/4 power if they were coming from the same direction, but why would you do that? if you are using multiple flashes, the main purpose is to have light coming from different directions, which wouldn't amount to 1/4 power from any one direction, but if you quantified the total number of photons flying around in your immediate area.. then i guess your answer is yes...

faster recycle time... just find it weird that it works that way, logic says its same strength of light but more of it...

zincozinco wrote in post #10172173
faster recycle time... just find it weird that it works that way, logic says its same strength of light but more of it...

visible light of the same spectrum (frequency) doesn't increase in intensity, only in volume.

if it got more intense (more energy) the wavelength would be changing to a higher energy wavelength, and ultimately would push out of the visible spectrum.

The simple fact is that two identical lights placed side-by-side will allow you to reduce your exposure settings by a total of one "stop". In other words, the light from the two is two times the light from one.

If you put the two lights in different places, such as on both sides of a subject, the results will be different.

zincozinco wrote in post #10172173
faster recycle time... just find it weird that it works that way, logic says its same strength of light but more of it...

because you think of it as an explosion of light, when it's really a flow limited by time. so 1/8 iz just flash working 8 times shorter than 1/1. it's the same intensity, color, whatever. it just works shorter

If you have two 580EX both set in manual to the same power setting, you will have 1 stop more light than one 580 EX set to power level.
for 2 stops more, you need another two speedlites (for a total of 4)

i have done this (2x speedlights side by side) to reduce the recycle time, and allow me to "keep the flow" of working with a subject, instead of standing around waiting for the flash to recycle

If you have more elaborate setups, then you may want to know that guide numbers add as the square root of the sum of the squares of the guide numbers for the flashes used.
An example: Combining one 580 EX II and one 430 EX II, both at full power and zoom, which implies guide numbers 58 and 43, add up to a combined guide number of 72. You can find the relevant guide numbers for different manual power settings and zooms in the user's manual for the flash.