The basic problem is that watts masure how much the light DRAWS from its
power source, and say little, if anything about how much light they put out.
There is no way to take this figure and calculate light output. I have never
understoond why manufactureres started measruing lights (light bulbs, studio
lights, bicycle lights, whatever) in watts. I also wonder why we continue to
do so. The information is really pretty much wortheless, unless you want to
know what it will cost you to run the lights, or how long the light will run
with a given battery.
Jim Couch
John Hudson wrote:
> I was told today that any two different brands of studio strobes each
> rated at 400 watts / second [or any other rating for that matter] might
> not deliver the same intensity of light output. By way of analogy my
> source said that in and of itself any particular strobe rating was like
> saying that an automobile's engine had four, or five, or six cylinders
> and so many valves but did not imply or specify the actual power output
> other than suggest, for example, that a 800 w/s rating was likely to be
> twice as intense as a 400 w/s rating.
>
> Can any one out there explain just how you measure the intensity of
> light output by reference to the watt per second rating and how this can
> be converted into a guide number for any particular ISO film speed?
>
> John Hudson
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