Question about continuous lighting wattage need

dsiglin · Jan 24, 2014

Preface: On the digital side of photography I use flash comfortably, but on the film side I want to see in advance how the light is going to wrap around my subject.

Question: Suppose I want to take a half body portrait at ISO 200-400 and f5.6-f8. Does anyone have a ballpark suggestion for what wattage I need from continuous lights? To make this trickier I would mostly be shooting with some natural light (maybe ISO 200 f 2.8 worth of it). So I'd need enough light to increase exposure by another say 3 or 4 stops. When I ask about wattage I'm talking about incandescent wattage. I understand for CFL and LED the actual wattage will be lower.

Addendum: I'd be shooting through a 48" Octagon softbox and/or 16" beauty dish with soft diffuser.

Thanks for your time and input.

dsiglin · Jan 24, 2014

I would be using something along these lines:
http://www.amazon.com/Full-Spectrum...8-5&keywords=multi+bulb+lighting++photography

They are 5500K, CRI 90-92, equal to about 180W Incandescent. If I use a softbox I would buy a head that accepts multiple (probably 5) of these. Let's suppose the softbox's diffuser eats 2 stops of light. I don't know if that is normal but I just picked a number to have something more concrete.

MattKrull · Jan 24, 2014

My continuous lighting setup is two shoot-through umbrellas, each holding a pair of 60w CFLs (total kit is supposedly equivalent to 1200w). I find once I place my lights (pretty darned close) I'm still running F3.5 1/60 ISO800 (I pushed Delta 400).

I just took a strobe class last night, and it really showed me just how little light I'm getting with my CFLs. The biggest bulbs I can buy are 150w each, which would give me roughly a stop and a half more light. That's still a few EVs short of what you want.

From your numbers, I'd aim for a 4000w equivalent kit. You'll need two bulb bases that hold four or five bulbs to get that.

On the plus side, the lights are easy to work with and don't produce much heat. You can put them very close to your subject without discomfort.

dsiglin · Jan 24, 2014

Excellent advice matt, what do you use to attach the bulb fixtures to your light stand and umbrella?

wildbill · Jan 24, 2014

most lighting manufacturers have photometrics for their fixtures online.

MattKrull · Jan 27, 2014

I'm using the cheapy light fixtures available under a bunch of names (adorama, cowboy studios, etc). The two-bulb holder has a proper light stand mount and an umbrella mount built in.

dsiglin · Jan 27, 2014

So for the fun of it I ordered this 2800 lumen bike light. The nice thing is the directional nature of the light and the reflectors built into it.
http://www.amazon.com/gp/product/B00C2MHNJK/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1

I'll report back with my findings and maybe some sample photos. I imagine I'll need two of these if it indeed seems to work.

dsiglin · Jan 30, 2014

I did some tests and was decently impressed by the results but I don't think it's workable unless you had three of these guys.

I found an answer to how many watts do you need after stumbling across this article where Neil vN used a 220 fluorescent watt softbox with ISO 800 f4.5 1/100. Not bad. That would be about 600 watts incandescent.

Jim Rice · Jan 31, 2014

It is much easier to deal with too much light than not enough.

dsiglin · Feb 1, 2014

Yes it is. Based on my tests and Neil vN's article I'd say you would want AT LEAST 1200 watts of directional incandescent light, or about 440 watts of directional fluorescent light.

ToddB · Feb 28, 2014

Great thread.. I've been curious with this technique. I have a Brown series Speedtron light setup. It's kind of limited in regards dailing down output. I'm alway shoot F16 or F22. I love that NDF look, but just can't achieve this with flash operation. I haven't tried using the sustain model light option. Might have to try it out this weekend.

Question about continuous lighting wattage need

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