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True WS. Effective WS studio light rating?


Hi folks,

I work for a furniture company and we are getting ready to invest in photography equipment to do our own in house photography for mostly web and some print. Most of our photos will involve individual pieces of furniture on a white sweep background. Medium sized sofas will be our biggest pieces to shoot. Of special consideration is getting good lighting with a clean "pure white background", and getting colors to be accurate to the actual fabrics. We shoot greens, browns, and reds which are often problematic.

We are considering getting the following:

A Canon 5D with an EF 15-35mm f/2.8L lens

My question regards this lighting:

Alien Bee B800 Monolight

They rate it at:

320 True Watt Secs./800 Effective Watt Secs.

-OR-

Flashpoint II 1220 Monolight

They rate it at:

600 True Watt Secs.

I gather that they rate their watts differently, and that it may be skewed to the high side. I'm guessing that this type of rating is similar to the power ratings that I am familiar with for car stereos. An amplifier for a stereo is rated in RMS Watts. The true RMS Watts represent the realistic power available from the amplifier at any given time. Peak RMS is a figure that represents the maximum power the amplifier could put out in an "ideal" situation. In other words, if an amplifier is rated @ 800 RMS Watts, and it's Peak RMS Watts is 1,000, it's likely that the ONLY time you are going to get 1,000 Watts out of the amplifier is when you have a perfect 12 Volt power source, and even then, only for about 30 - 60 Sec. until the amplifier heats up and it begins to drop in power to cool down the electronics.

So my question is, in theory, is True Watt Seconds vs. Effective Watt Seconds similar to the power rating system I described above for amplifier ratings?

If my assumption is correct, would I be better off going with the B1600 rated at 640 True WS because that is a more accurate comparison to the Flashpoint II?

If that's the case, then we would probably opt for the Flashpoint II, because a set of two lights would be $127 cheaper then buying 2 Alien Bees 1600s.


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August 22, 2006

 

John H. Siskin
  The problem with watt-second ratings is that they are a rating of power consumption by a unit rather than light output. As a result of this certain manufacturers who have more efficient systems, the produce more light from the power, want to show that actual light output. They talk about true watt seconds where they compare their lights to an inefficient system. This is even less helpful that the original watt-second rating. In this way watt-second ratings are perhaps even more inaccurate than RMS ratings.

You will probably need more like 750 to 1000 watt-seconds, normal watt-seconds, per light to shoot furniture. You will probably need 3 or more lights. You will want some large diffusers, like umbrellas to spread the light. Also a white seamless does not photograph as pure white, you may need to cut your sofa out from the background in Photoshop.

There are some lighting articles on the magazine page of my website:www.siskinphoto.com. They may be of help to you.

Your camera is probably an excellent choice, but remember to do accurate white balances with it.

Good Luck!
John Siskin


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September 04, 2006

 

Pete H
  Your analogy is a good one and pretty close to being right on.
As John correctly pointed out, True W/s Vs. Effective W/s are power consumption numbers.
To use your own analogy Jason, I've listened to 10 watt amplifiers that blow away the so called 100 watt amps..it all comes down to HOW the power is utilized.

If one wants to get really nuts, do a Lumen measurement..Or, a flashmeter to compare output.

More to the point, Two 1000 W/s true output strobes will no doubt be sufficient for your needs.
For a pure white background, you will probably need a couple more strobes.


Pete


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September 05, 2006

 
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