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I've been using my dad's old incandescent studio lights (Smith-Victor) but decided to buy some CFL lights instead so it's not so hot under the lights. I got some cheap Fovitec ones from Amazon (supposedly 105W though I doubt it) and they seem to work just fine, but I was previously using TRIAC dimmers and these obviously don't support dimming.

I'm using both shoot-through and reflector umbrellas for a few different lighting setups. I don't know if these old lights can take something like a theatre gel but the CFLs stick out past the edge of the fixture anyways. How can I dim these, either in steps (25%, 50%, 75% etc.) or continuously (like a dimmer)?

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How can I dim these, either in steps (25%, 50%, 75% etc.) or continuously (like a dimmer)?

Absent the option to adjust the intensity of the bulbs themselve you have less than a handful of options:

  • Vary the distance between each light and the subject. The inverse square rule applies: Doubling the distance means 1/4 the light per area falls on the subject which equates to two f-stops. Increasing the distance by the square root of two (1.414x) reduces the effect of the light by one stop. Halving the light-to-subject distance increases the effect of the light by two stops. Changing the distance by 1/√2 (.707x) increases the effect of the light by one stop. Note that changing the distance of the light may well change the shape of the light as well as the angular size of the light as measured at the subject will be reduced as you move the light further away.
  • Stop down your camera's aperture. Each full f-stop on the camera is equal to reducing the light's intensity by half. Of course using the aperture will affect all lighting sources equally.
  • Shorten the camera's shutter time. Each full stop reduction in exposure time on the camera is equal to reducing the light's intensity by half. Of course using the shutter time will affect all continuous lighting sources equally.
  • Increase the opacity of your shoot-through modifiers and decrease the reflectivity of your reflective modifiers.
  • I hadn't considered the inverse square law. Oddly enough I know about it from engineering but didn't consider it in regards to photography. Combined with a low-opacity shoot-through umbrella used as a reflector this seems to be appropriate for my needs. Not as convenient as dimmers, but functionally equivalent! – gjsmo Dec 27 '16 at 21:50
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CFLs don't dim. LEDs will dim but often have weird dimming curves. My suggestion would be to keep using incandescent bulbs.

Edit: note that CFLs are either all on or all off. You can't set it at steps or dim it continuously.

  • I suspected it wouldn't be dimmable at all. Is there a good source for new incandescent bulbs? I've been using my dad's old stock but at the moment there's only two left which is just enough to run my two lights. – gjsmo Dec 26 '16 at 2:44
  • I don't know about brick and mortar stores, but there should be plenty of online options. In the United States, 1000bulbs.com looks like a good option: 1000bulbs.com/category/100-watt-standard-shape-light-bulbs – NoahL Dec 26 '16 at 2:55
  • CFLs dim just fine unless they're designed wrong. The backlight in your computer is basically just a CFL. However, when you dim a CFL (or, for that matter, an LED if you want it to dim more linearly), you use a PWM circuit to chop up the power. The duty cycle determines the brightness. – dgatwood Dec 28 '16 at 12:38
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If the fixture might hold multiple CFL bulbs, you can simply remove one or two.

My experience with Fovitec CFL bulbs was that their "85 watt" bulb only measure 50 watts (technically, it consumes 85 VA, but which is only 50 watts).
Try Alzo brand for honest rating.

  • Good old power factor. I'll check out Alzo, thanks. And no, they're single fixtures like this. – gjsmo Dec 26 '16 at 2:46

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