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DPChallenge Forums >> Tips, Tricks, and Q&A >> True or Effective Watt seconds?
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10/28/2005 04:32:48 PM · #1
Can someone explain the difference to me?
I'm guessing True is the actual watt seconds a light has and Effective is something like what it is actually capable of performing at? Something like that? Even guessing that I'm foggy.

Can someone tell me? I'm looking at strobes and I find some of the specs confusing or even misleading.

10/28/2005 04:47:42 PM · #2
I basically want to know if when they list effective watt seconds for a strobe if they're just trying to make it sound better than it is? lol
10/28/2005 05:43:39 PM · #3
From the Paul C. Buff web site:

Quantity of electrical energy is measured in Wattseconds, also known as Joules. This rating defines the amount of electrical power discharged with each flash. While the actual amount of light produced for a given number of wattseconds varies, depending on the unit's design, the term provides a reasonable guide to comparative light output, as long as real/true wattseconds are specified. In the conversion of Watts to Lumens, or Wattseconds to Lumenseconds, the efficacy of the system determines how much light will result from a given number of wattseconds. The poor efficiency in this conversion by manufactures has given rise to the term Effective Wattseconds. If one flash system converts 400 Wattseconds of energy into 16,000 Lumenseconds of light, and another flash system converts 800 Wattseconds of energy into 16,000 Lumenseconds of light, then the first system could claim to have "800 Effective Wattseconds" as it is effectively producing the same amount of light as a system starting with 800 True Wattseconds. The Effective Wattseconds rating, however, is rather arbitrary and cannot be easily proven true or untrue, as it is merely used as a basis for inflated comparison of different flash systems.

Message edited by author 2005-10-28 17:45:49.
10/28/2005 10:52:23 PM · #4
Oh thanks so much. I didn't think anyone had responded but decided to check just in case.

Thats just what I wanted to know.
10/28/2005 10:56:43 PM · #5
A similar explanation i got from Lumedyne also takes into consideration the reflector or other light modifer - a reflector can make the light spread very little or a lot, so measuring the lumens at a given point and distance would mean very little. Then when you add softboxes, etc things change all over again. WS measures power in more so than light output.

It is all smoke and mirrors. The on-camera flash guns are all rated in GN, guide number. with TTL these days that means nothing, but bigger is still more powerful.

No, before you ask, there is no conversion from GN to WS of any kind.
10/29/2005 05:11:59 PM · #6
well, no real standard, since the reflector plays a BIG roll in Output quantity.

Go by "effective WS" with the supplied reflector. BUT the GN will change with different reflectors> Following from Photogenic Studiomax II manual for AK320ws strobe.
No reflector = GN 51
7.5" = GN 170 (supplied with unit)
14" = GN 143
16" = GN 163
20" = GN 138
24" = GN 70

It is the reflector that adjust's the GN. The WS are the the same. But the reflectors can use the output MORE or LESS effectively.

Hope this helps
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