By John Siskin
I teach several classes about lighting, so I wanted to take a few words to try to help everybody understand some of the basic things about strobe lights. A professional strobe actually has very few controls. Strobe power output, model light output, on/off for the model light, on off for the internal slave and power, and not every strobe has all of these. The most important control is strobe power output; on some strobes this is the only control! Not only is it the most important control; strobe power is the most important factor in what strobe to buy.
 Calumet Travelight 750 © John H. Siskin All rights reserved |
The whole problem with talking about strobe power and buying strobes is that the units we use to discuss power don’t make a lot of sense. Of course it’s not like f-stop numbers such as 2.8, 5.6 and 11 make a lot of sense either. In the case of strobe power we use watt-seconds, which doesn’t measure light at all, but measures electrical power. Watt-seconds are used to designate the power of a strobe unit, say 600 watt-seconds, in the same way that the maximum aperture is used to discuss the light gathering capability of a lens. Photographers have a way of talking about light output from a strobe that really measures light, it’s called guide numbers. The problem with guide numbers is they are affected by the reflectors and diffusers you put on a light; so a light with a brighter reflector will have a higher guide number. The idea of the watt-second ratings is that all strobes have a similar efficiency at turning electrical power into light; this is true. Some of the manufacturers have think that they have more efficient systems for reflecting the light so they should give themselves higher watt-second ratings, calling their ratings things like effective watt-seconds, this is an unfortunate and confusing practice. The problem is if you are using a soft box or other diffuser the advantage of a brighter reflector goes away, since you aren’t using a reflector.
 Small Light Source Set-up © John H. Siskin All rights reserved |
One of the questions I get asked is how much light is enough? The answer depends on how you use the light, direct or diffused. In the studio I use a lot of diffusion, often both an umbrella and a light panel, so I get lights with at least 600 watt-seconds. For location work I use light more directly so I can get by with lower power lights; I often take 200 watt-second battery powered lights on location. As with purchasing any equipment it is important to understand your goals for the equipment. I am fortunate enough to have different lights for different jobs. If I had just one sort of light it would be monolights of 600 watt-seconds or more.
Have a great weekend!
John
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