>From high school physics I remeber a watt is a unit of
electricity while a lumen is a measure of light. A 25w
flourescent lamp can equal a 100 watt incandescent in
lumens due to the fact that it is more efficient at
converting electricity into heat. If the strobes are
made of the same stuff and use the same amount of
electricity their light output should be about the
same or the same. Check their output in lumens though,
that'll give youthe amount of light they put out,
wattage is just how much power they suck up and is a
measuring block for similarly built items like
incandescent light bulbs.
As for comparing and converting to ISO I have no idea,
I just let the cameras light meter do all that
thinking for me. But there probably is a lumens/sec
thing on the web which would say that an ISO 100 speed
film will be some 0.000000e+00xposed by this many lumens at 1
second. I have no idea what the formulas are for such
a task.
Mark Lloyd
--- John Hudson <jahudson@xxxxxxx> 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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