A very common designation these days is the "effective watt seconds" for strobe output. There are a lot of disagreements about the value of this designation and if it is based on reality or a marketing fabrication. I have long wondered about strobe output and the comparison between my pack and head system and a very common modern monolight.

Last month at the monthly social I host at my studio, I had the opportunity to test my Bowens pack system against two different monolights with high "effective" w/s designations. Both of the monolights had a designation of 1600, with an true 640w/s output. I put identical Bowens-style 7" reflectors on both strobes and aimed them at a wall 15' away.

Here's where I explain that I was just looking for a baseline idea of output, not trying to do anything more scientific than simple A/B comparisons. I did not test light quality nor am I claiming that my comparisons are 100% exact.

The monilights at full power both had an output that gave me f/22 at 15' underexposing a white wall by 1 stop -- that's a guide number of 240. To reach the same output with my older Bowens Estime pack and head, I needed to dial in 1000 w/s -- so, in my estimation, the monolight is almost twice as efficient, but still falling short of the "effective" designation. This designation may be more in-line with the output of older norman or speedotron packs, but I don't have any to compare.

What I learned is that the "effective" designation is not necessarily accurate, nor is it as much a fabrication as I had previously believed. I also saw variances in the monolights color temperature and overall output from one image to the next - it was clearly visible in my color histogram on the D3X. I didn't have a lot of time with the lights and wasn't in an environment where I could test accurately and come to a scientific conclusion. My general impression is that I'm very happy with my Bowens gear, but I'm certainly not going to be a gear snob about it - there are good reasons to buy less expensive equipment,including significant output for the investment and less expensive replacement tubes - but there are definite advantages to the big pack systems or pro-name monolights : light quality, consistency, rental availability, maximum ouput on each of my 3000 w/s pack exceeds any available monolight.

I have some colleagues with Profoto and Dynalite systems, so I will definitely be rounding up some equipment for a shootout.