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true watt seconds and effective watt seconds
Jason Arnold, Photo Editor, Photographer
Fort Lauderdale | FL | usa | Posted: 8:43 PM on 07.18.05
->> Hi everyone, Just one quick simple question, true watt seconds and effective watt seconds what is the difference?
Thanks!
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Chris Livingston, Photographer
Orlando | FL | United States | Posted: 9:30 PM on 07.18.05
->> Jason

It is White Lightning Marketing vs. real world. Compare apples with apples and look at the true WS numbers.
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Peyton Williams, Photographer
Durham | NC | USA | Posted: 9:42 PM on 07.18.05
->> Hey Jason,

FIrst, remember that watt-seconds measure INPUT of power, not output. With that, a high quality 2400 Ws may be brighter than a lower quality 2400 Ws unit.

The actual input is the true Ws.

Marketing genius is behind effective Ws. "We think our 800 Ws pack puts out as much power as a 'another' 1200 Ws pack".

'Another' could be a poor performing unit they use for comparison.

In any case, Ws (true or effective) isn't going to help you much is comparing units. Two ways (that I know of): Get a light meter and test them for yourself. Or look at the guide numbers.
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Jason Arnold, Photo Editor, Photographer
Fort Lauderdale | FL | usa | Posted: 11:28 PM on 07.18.05
->> Hey Chris and Peyton, Thanks alot for clearing that up for me!
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Greg Ferguson, Photographer
Scottsdale | Az | USA | Posted: 12:31 AM on 07.19.05
->> It's the same sort of numbers games as with T1 and T2 flash decay rates, wattage and distortion ratings for power amplifiers, CPU speeds among different processor technologies and gas mileage on new cars.
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Paul Montague, Photographer
Swisher | IA | USA | Posted: 12:28 PM on 07.19.05
->> One Watt-second is one Joule of energy -- the work done when one amp of current is passed through one ohm of resistance for one second.

Watt-seconds, when describing strobes, are a measure of the amount of energy that can be output from the power supply and delivered to the flash head(s).

The light output from the flash head will depend upon the energy delivered to it, the design of the flash tube, and the reflector among other things. So Watt-seconds alone are not a measure of light output.

Beam Candle Power Seconds (BCPS) are a measure of light output which is dependent upon the angle of light dispersion from the reflector. As Peyton already mentioned, Guide Numbers are also a measure of light output. They will vary by the angle of the reflector as well, with a wider reflector yielding a lower GN.

When comparing two strobes with fixed angles of coverage, either BCPS or GN should be useful.

When comparing two strobes with interchangeable reflectors or variable angles of coverage, look at the BCPS or the Guide Numbers, but make sure the numbers are quoted for the same angle of coverage.

When comparing two power supplies for the same strobe head, Watt-seconds can be used to tell how those two power supplies differ. However, the correlation between WS and light output may not be linear (doubling the WS might not double the light output).

"Effective" Watt-seconds sounds like "marketing" to me.

Paul
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Matt Cashore, Photographer
South Bend | IN | USA | Posted: 1:12 PM on 07.19.05
->> Allow me to muddy the waters further...I used the old WL1800s for arena lighting years ago. Then I got the Elinchrom 500w-s lights. The Elincroms were a little brighter, even though 1800w-s sounds like it should be 3x more powerful than 500w-s. In my experience (Using White-Lightning, Elincrom, and Dyna-Lite gear) the true watt-second output seems to be uncannily close to a 1:1 ratio of the number of dollars you spent. The $300 monolight? 300w-s. The $2000-ish pack/head combo? 2000w-s. You get the idea.
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Paul Montague, Photographer
Swisher | IA | USA | Posted: 1:21 PM on 07.19.05
->> If your strobe is rated in "Effective" WS, do you get to pay in "Effective" dollars?
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Rich Gabrielson, Photographer
Rapid City | SD | USA | Posted: 3:37 PM on 07.19.05
->> I've kind of wondered if they weren't playing around with duration as well to come up with 'effective' ratings. For action stopping of course you would want as much power in as short as time possible. If you don't have the power but could extend the duration an arugument could be made that the exposure is the same since the duration is longer, (but still shorter than the time the shutter is open for sync'ing) that 'effectively' longer duration lower powered units would expose at the same setting as a higher power shorter duration units. That would not calculate out in true Ws however, so we need to call it something else.

I've confused myself.

Rich
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Rich Gabrielson, Photographer
Rapid City | SD | USA | Posted: 4:17 PM on 07.19.05
->> After doing some research because I've wondered this myself, what Paul and Peyton are saying seems to be true. True WS can accurately be measured as Paul says. As Peyton says, some manufacturers believe or would like you to believe their units are better at converting this energy to light output than their competitors. It would seem this feeling is highly subjective, so trying to use math and science reason it out is hopeless.

Anyway next time I'll try to do some effective research before I post.

Rich
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Jim Colburn, Photographer
Omaha | NE | USA | Posted: 10:00 PM on 07.19.05
->> "true watt seconds and effective watt seconds what is the difference?"

Watt-Seconds = an international standard
"True" watt-seconds = Marketing BS

Go for the guide number, that's how you can tell how much light comes out (and remember to factor in reflectors and such.)
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Vern Verna, Photographer
Greenville | SC | United States | Posted: 10:20 PM on 07.19.05
->> jim hit it on the head use the guide number. they dont lie.

gn / fstop = distance object is lit at that exposure. ie
100 gn / f4 = 25 ft. light throw.

a wl 1200 in my experience is equal to about a 500 ws speedo black line with a 16' reflector. or if i put my speedos in an arena next to a wl 1200 set. i shoot a 4 1/3 and they shoot at 2.8 at the same asa.

elinchrome and speedo ws are close to the same thing. the other thing is the reflector used. the biggest elinchrom reflector will make the thing give a little more light than an equivalent speedo with a 16" sports reflector on it. the middle elinchrom gives about the same light as a speedo with equivalent ws.

a dynalite with their big long reflector gives about 1/3 to 2/3 less of a stop than a equivalent speedo. or in other words a 2000 ws dynalite is about 1300-1500ws of a speedo.
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Jim Colburn, Photographer
Omaha | NE | USA | Posted: 9:57 PM on 07.20.05
->> And be sure to measure (at home) the guide number of EACH unit with reflector and with the carried umbrella and write those numbers on the side of each unit with a Sharpie. If you lose you meter or its batteries die you can (or should be able to) figure out the correct exposure even with multiple lights.
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Jason Arnold, Photo Editor, Photographer
Fort Lauderdale | FL | usa | Posted: 2:21 PM on 07.21.05
->> Thanks again everyone!
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Alan Look, Photographer
Bloomington | IL | United States | Posted: 8:16 PM on 03.01.08
->> Need to reach back in time and kind of change the topic of this old thread...

I'm trying to compare my 580 flas to a monolight. I'm not sure I'm getting all the information, or maybe I'm getting too much and getting confused....

THe 580 has a guide number of around 190 @ 100 ISO and the zoom head set at 105. The guide number of the same unit with the head zoomed at 50 is about 138.

The monolight specs are F-stop, (1m, 100 ISO, 1/250s, Reflector 48*) = 64.1

I'm having a hard time believing that the speedlight uts out over twice the light as the monolight. I've decided that (becasue of the discussion in this thread) that the guide number system would be better to compare with than the watt-seconds (which I couldn't find for the speedlight anyway).

Anyone care to tell me what I'm missing/misinterpreting?

BTW - The monolight I'm using in the example above is a 300RX Elinchrom. The guide number on the 600 (another one I'm interested in) is better, but the recycle times and flash duration are longer.

Thx in advance.
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Ron Manfredi, Photographer
Merrick (Long Island) | NY | | Posted: 8:56 PM on 03.01.08
->> Alan,

Not sure I understand. The GN of 190 means using f/19 at 10 feet. If I read your post correctly, the monolight with the 48" reflector is f/64. That should mean that the monolight is about 2 stops brighter.


->> THe 580 has a guide number of around 190 @ 100 ISO and the zoom head set at 105. The guide number of the same unit with the head zoomed at 50 is about 138.

The monolight specs are F-stop, (1m, 100 ISO, 1/250s, Reflector 48*) = 64.1 -
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Thread Title: true watt seconds and effective watt seconds
Thread Started By: Jason Arnold
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