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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 01 Nov 2010 (Monday) 14:23
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watt vs w/s ratings. Or continuous lights vs strobes

 
blocks
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Nov 01, 2010 14:23 |  #1

How do you compare continuous lighting watt output with strobe's watt/secs? If continuous lighting is watts per hour can I just divide by 3600 to get the equivalent w/s rating? I can have a 600w continuous lighting source and it barely puts out enough light whereas a strobe at 10 w/s can overexpose a pic. So, does 600watts/3600= .17w/s?




  
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Tawcan
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Nov 01, 2010 15:14 |  #2

It's actually ws for strobes not w/s. Ws is the same as J (Joule) which translates to the amount of energy stored in strobe's capacitors.

A quick googling found this link:

http://webs.lanset.com …an/flash/hotors​trobe.html (external link)


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Tobi.
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Nov 01, 2010 15:44 |  #3

blocks wrote in post #11205376 (external link)
How do you compare continuous lighting watt output with strobe's watt/secs? If continuous lighting is watts per hour can I just divide by 3600 to get the equivalent w/s rating? I can have a 600w continuous lighting source and it barely puts out enough light whereas a strobe at 10 w/s can overexpose a pic. So, does 600watts/3600= .17w/s?

It's Ws = Watt*seconds for strobes, as Tawcan pointed out. Continuous is just plain Watt.

Now if you want to convert from strobes to continuous just look at the units: 1Ws = 1W * 1s. So if you've got a strobe with let's just say 400Ws and want to know your equivalent continuous light for a shutter speed of 1/125s to avoid motion blur, you'll need
400Ws/(1/125s) = 400W * 1s/(1/125s) = 400W * 125 * s/s = 400W * 125 * 1= 50.000W.

Get a pencil and write it down, the presentation in one line is quite confusing. If you're writing this as normal fractions, it will be obvious.

The joys of SI units.

Tobi




  
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munzzzzzzz
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Nov 01, 2010 16:21 |  #4

Tobi. wrote in post #11205917 (external link)
400Ws/(1/125s) = 400W * 1s/(1/125s) = 400W * 125 * s/s = 400W * 125 * 1= 50.000W.

Tobi. wrote in post #11205917 (external link)
The joys of SI units.

Speaking of SI units, also keep in mind that the "." used in many countries in "50.000W" is actually a "," in the U.S., i.e. "50,000W".


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Tobi.
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Nov 01, 2010 16:31 |  #5

munzzzzzzz wrote in post #11206143 (external link)
Speaking of SI units, also keep in mind that the "." used in many countries in "50.000W" is actually a "," in the U.S., i.e. "50,000W".

Yeah, sorry. That one always confuses me since in Canada SI units are used (At least they're supposed to be used, but try getting a 3mm drill bit in a hardware store! 3.18mm is no problem at all...) but ',' as separatur between thousands. I kinda mix that up every once in a while...

Let's just say that I meant 5*10^4W. ;-)a

Tobi




  
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SkipD
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Nov 01, 2010 17:16 |  #6

Tawcan wrote in post #11205733 (external link)
It's actually ws for strobes not w/s. Ws is the same as J (Joule) which translates to the amount of energy stored in strobe's capacitors.

On top of that, one must realize that you can have a half-dozen different makes and models of flash units - all having the same Ws rating but each putting a different amount of light on the subject when set up the same way and at the same distance.

The reason is simple. Variations in circuitry, flash tube design, reflector geometry, reflector surface type, etc., all affect how much light is put on the subject.


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Wilt
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Nov 01, 2010 18:30 |  #7

SkipD wrote in post #11206541 (external link)
On top of that, one must realize that you can have a half-dozen different makes and models of flash units - all having the same Ws rating but each putting a different amount of light on the subject when set up the same way and at the same distance.

The reason is simple. Variations in circuitry, flash tube design, reflector geometry, reflector surface type, etc., all affect how much light is put on the subject.

^
...and even for continuous light bulbs, the Watt rating simply tells electrical consumption -- much of it simply converted to HEAT and a portion of it converted to LIGHT. A visit to a hardware store and a look at several different models of 60W bulbs will disclose that they will produce a different amount of light (measured in Lumens).


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watt vs w/s ratings. Or continuous lights vs strobes
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