Lumens vs. lumenseconds

Started Dec 9, 2012 | Discussions thread
Suntan
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Re: Lumens vs. lumenseconds
In reply to ekomorgan, Dec 10, 2012

ekomorgan wrote:

I have a couple of octacool-9 fluorescent lights made by Impact. I was quite surprised by the lack of light I get from them. When I photograph kids in my small in-home studio, I typically need to shoot at 800 iso in order to get a high enough shutter speed to stop their quick movements. B&H says that each light puts out 12,600 lumens. I was looking at the alien bee 800's and it says they have 14,000 lumenseconds. These numbers seem pretty close, but i am pretty sure the alien bees aee more powerful and would allow me to shoot at a lower iso. It there a difference between lumens and lumenseconds? Trying to understand why these seemingly bright lights are not allowing me to shoot at a lower iso?

If you set your shutter speed to 1 second, then you will get the 12,600 lumen-sec out of your continuous lights. The downside is that you will also get a lot of subject motion blur if you are shooting kids. If you set the shutter to 1/2 second, you'll only be getting 6,300 lumen-sec. 1/4 second shutter will give you 3,150, etc. etc. ...Once you get to a shutter speed of even 1/60 second (still not fast enough to really stop subject motion, imo) you are down to as little as 210 lumen-sec.

At 1/200 shutter speed, you're only getting 63 lumen-sec. Not much.

With the ABs, you can get 14,000 lumen-sec even at your sync speed (and the actual flash duration is even much faster than this) making for all that light in a really short span of time so motion blur is all but eliminated.

-Suntan

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