Light power?

[seismiccwave]

<p>Ok this question doesn't fall into any specific category. So I just put it under studio lights. I use studio lights in my studio. Specifically I use four Alien Bees. Three each 800 and one each 1600. I noticed the size of the Alien Bees are expressed as watts-second. The 800 is 800 ws etc.<br>

I am sure I can find the answer if I do a better search but I am pretty lazy. I am so used to using those camera flashes that were expressed in guide numbers. <br>

So are there any smart people that can explain to me how to translate between guide number and watts-second?</p>

<p> </p>

[danny_wong2]

<p>Watt/sec is a measurement of the potential electrical energy that can be discharged to the flashtube which converts it into light energy.<br>

Guide number is a numeric system that measure the amount of light shine onto a subject to simplify exposure calculations<br>

If someone can directly translate WS into GN without considering all the other factors involve they would be very smart.</p>

[richard_quindry]

<p>Unfortunately, you can't translate watt seconds to a guide number. Guide numbers relate to a particular flash head / reflector combination. Watt seconds tells you how much energy is available to put out. <br>

Because studio lights accept numerous reflectors,softboxes, umbrellas, etc. and because each of them absorbs and distributes light differently (a highly silvered narrow angle reflector that concentrates the light over a smaller area, a 4'x6' softbox with a white interior and an interior baffle installed to even out the light, a bare bulb flash that sends light in almost all directions) the amount of light that reaches a subject 6 feet away can vary wildly.<br>

You need to either measure them with a light meter or study the histogram and image on the back of a digital camera to determine the proper amount of power to send to the flash head for a given aperture.</p>

<p>Hope this helps.</p>

<p>Richard Quindry</p>

<p> </p>

[Alan Marcus]

<p>The output of an electronic flash is dependent on many factors. One key factor is the amount of energy applied to the flash tube. This valve can be calculated or measured by the manufacture. However, now we must take into account the efficiency and distribution of the reflector or diffuser.</p>

<p>Now the electrical energy supplied to the tube is via a capacitor. This is an electronic component, the best way to describe is:</p>

<p>Low water pressure makes putting out a fire in the barn dubious. A water facet supplying a low volume is allowed to slowly drip into a bucket. The bucket accumulates water over time. The bucket is now available should the need arise for a large volume of water. A fire breaks out, you grab the bucket and in one swish, put out the fire.</p>

<p>This is the circuit of the electronic flash. We need a huge supply of electrical charge to smack the flash tube with speedily. Our power supply, be it from the main or battery is too feeble. We cause a charge to trickle into reservoir, which will store and hold the charge. This electrical component is called a capacitor.</p>

<p>You press the go button on the camera and the capacitor hastily dumps the charge into the flash tube which releases bottled sunlight.<br>

The formula :<br>

Watt seconds =(capacitance stated in microfarads x voltage)^2 ÷ 2,000,000. </p>

<p>Now I know that means a lot to all! Are you satisfied with this gobbledygook?</p>

<p>The answer should be no because it’s a poor way of describing the light output. Manufactures love complicated specifications with high values because they are under an illusion this will somehow help sales. (I was guilty too).</p>

<p>A better ratting system is to express the output in effective candlepower seconds. From this information we can derive a guide number. The formula:</p>

<p>square root (0.63 x ECPS x ISO).</p>

<p> The problem is few publish the ECPS so we are forced to perform a practical test. Lamp at 10 feet from subject. Shoot a series at all apertures at 100 ISO. Have the subject hold a placard indicating the aperture of the exposure. Select the best frame. Multiply aperture used times 10. The result is a useable guide number for that studio configuration and ISO setting. </p>

[Charles_Webster]

<p>And to make things more confusing, and AB 800 is not 800 ws, but only 320 Ws, and the AB1600 is only 640 WS, not 1600.</p>

<p>Read the specs on the website. They give the real information. Even the side of the strobe gives the correct power.</p>

<p><Chas></p>

[bob_sunley]

<p>Buried on the AB web site are the GNs for the various models with a reflector.</p>

 

[seismiccwave]

<p>LOL, thank you every one for your explanation. How wonderful those numbers are to us!</p>

[peter_gaunt]

<p>What a strange unit. A watt is a joule per second so my guess is that a watt second is a joule, so why not just say so?</p>

[Alan Marcus]

<p>The watt-second is popular only in the USA. To the rest of the world its joule. After all only the US and Liberia have failed to adopt the metric system. In the US we use miles, inches, cups, hands, feet, yards, grains, barrels, caret, and hogshead, etc. </p>

[Matt Laur]

<p>Standards are boring, Alan. My AB800's put out 93 million lumo-candles per fortnight, with the standard reflector, at six paces.<br /><br />I just never worry about it. Out comes the meter, and I know what I've got. After a while, you're able to look at the scene, the ambient light, your subject, your distances, and just say, "If I'm using an AB800 as key in a large softbox a few feet from the subject, I'll probably need it at almost full power so I can use ISO 200 at f/11." You just don't have to do it for long before you can get very close in that way, and then tweek a bit before you go for that show-stopping shot.</p>

[peter_gaunt]

<p>Thank heavens for that. I thought I might be losing my marbles.</p>

[model mayhem gallery]

<p>GN, watts per second, joules what does any of this have to do with photography? I have model, any light, camera and action. I haven't used my light meter since I used my ELAN 7NE, which was way back when I got kicked out of photography class for cheating on the final. It was a Black and White film only class. I got an A but got caught when some saw the digital image on my Macbook. </p>

[nathan_stiles]

<p>MP, it has to do with shopping for photography. Same with power tools, if you buy that 0.8 amp chain saw, you are not going to cut down that hickory tree. It's nice to understand what you are buying; there's no knowledge that's not power.</p>

<p>Btw, I use my light meter on every shoot-- it saves time.</p>

[seismiccwave]

<p>MP it doesn't have anything to do with photography. I want to take a flash unit outdoors and want to see what is the big difference between the Alien Bees in the studio and the Nikon flash units. The flash units for the camera outdoors seems a bit under power and the Alien Bee with a power pack like the Vagabond is a bit too heavy. I wish some one has something in between. What ever happen to the old style Honeywell Strobonar with a power pack?</p>