Our first round of testing covers a couple of really basic things: straight light output, and reflector performance.

Power output ratings are a particularly slippery slope in comparing lighting systems. Most packs are rated in Watts/Second, or Ws. Watts are basically the electrical work done. Watt-seconds measure how much work is done over the period of a second. Broncolor, characteristically, defies the convention by using the term Joule, which is nothing but another name for a watt-second. The 3200 Joule Scoros pack would be equivalent to a 3200 Ws version of any other pack. In any case, that doesn’t tell us anything about the light output, just the electrical output. Measuring the light output is deceptively tricky too, because it depends so much on the type of reflector you’re using. The answer is, in our judgment, to simply compare the output with no reflector - just the bare flash tube. Fortunately, both of these systems have no built-in reflector in the heads, so a bare-bulb test was as close to equal footing as we were going to get.
 

We measured the exposure two ways. First, we determined the exposure using the histogram on the camera, comparing the values shown for the two systems. Using this method, you can get a very precise, and graphic evaluation of the differences between exposures. We also used a good quality flash meter that displays tenths of stops. We set the lights up at identical distances, with bare bulbs, made exposures and evaluated them.

The results? These two systems, one rated 2400 Ws, one rated 3200 Joules (or Ws) produced exactly the same light output at the highest power. We also tested at half and minimum power. They are identical, whether you look at the meter or the camera.

Why is this? There really is no way to say, definitively, and there’s really no point in speculating. Either the ratings are determined differently and produce different estimates of the charge, or they are accurate and the Profoto system somehow uses the charge more efficiently, but the end result is the same. The outputs between the two systems are identical.