Question about continuous lighting wattage need

Discussion in 'Lighting' started by dsiglin, Jan 24, 2014.

  1. dsiglin

    dsiglin Member

    Messages:
    35
    Joined:
    Dec 23, 2013
    Shooter:
    Medium Format
    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.
     
  2. dsiglin

    dsiglin Member

    Messages:
    35
    Joined:
    Dec 23, 2013
    Shooter:
    Medium Format
    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.
     
  3. MattKrull

    MattKrull Subscriber

    Messages:
    302
    Joined:
    Sep 2, 2013
    Location:
    Ottawa, Onta
    Shooter:
    Multi Format
    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.
     
  4. dsiglin

    dsiglin Member

    Messages:
    35
    Joined:
    Dec 23, 2013
    Shooter:
    Medium Format
    Excellent advice matt, what do you use to attach the bulb fixtures to your light stand and umbrella?
     
  5. wildbill

    wildbill Member

    Messages:
    2,851
    Joined:
    Nov 28, 2004
    Location:
    Grand Rapids
    Shooter:
    Multi Format
    most lighting manufacturers have photometrics for their fixtures online.
     
  6. MattKrull

    MattKrull Subscriber

    Messages:
    302
    Joined:
    Sep 2, 2013
    Location:
    Ottawa, Onta
    Shooter:
    Multi Format
    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.
     
  7. dsiglin

    dsiglin Member

    Messages:
    35
    Joined:
    Dec 23, 2013
    Shooter:
    Medium Format
  8. dsiglin

    dsiglin Member

    Messages:
    35
    Joined:
    Dec 23, 2013
    Shooter:
    Medium Format
    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.
     
  9. Jim Rice

    Jim Rice Member

    Messages:
    227
    Joined:
    Jun 7, 2006
    Location:
    Jackson. MS,
    Shooter:
    Multi Format
    It is much easier to deal with too much light than not enough.
     
  10. dsiglin

    dsiglin Member

    Messages:
    35
    Joined:
    Dec 23, 2013
    Shooter:
    Medium Format
    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.
     
  11. ToddB

    ToddB Member

    Messages:
    1,136
    Joined:
    Jul 10, 2012
    Shooter:
    Medium Format
    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.