Lumens - What the heck is going on? at
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Old February 27th, 2008, 12:19 PM   #1
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Lumens - What the heck is going on?

I recently came across something interesting - data that conflicts with "common knowledge" about the efficiency of fluorescents.

A 55w flo tube (the kind that go in the Diva Light, Caselight, and Coollights stuff) is rated as outputting 2800-2900 lumens. Thus, in the common four bulb fixtures out there, there would be a little over 11,000 lumens. These fixtures, which are 220w fixtures, are commonly known to have an output equivalent to almost 900w of tungsten light. However, a 750w tungsten bulb (say, one for a Lowel Tota) is rated as outputting almost 20,000, significantly more. What's the deal with this?

I know the fluorescents are still way more efficient. I'm just trying to make sure I'm understanding things the right way when I'm planning lighting setups with flos. Are the tubes really 4 times as efficient or is my confusion just a matter of softer light giving off fewer lumens than hard light of similar wattage? Not that I've typed that, that seems to be a logical reason, but could someone verify?


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Old February 27th, 2008, 12:56 PM   #2
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Generally the manufacturers are saying a 2-lamp, ie., two 55 watt lamps, fluorescent is roughly equivalent to a 500 watt "hard" light, and a 40 watt LED (like the ones sold by Flolights) is the same.

The problem is, a 500 watt hard light projects out more light than the equivalent fluorescent or LED. What you have to do is put the hard light in a softbox or diffuse it so it is equivalent to the fluorescent and then you can make a valid comparison. In the real world, measurebating over this isn't as effective as looking at the lights in the flesh.

I used three Lowel Caselights (two Caselight 2s and one Caselight 4) for several years and did a lot of interviews and even on screen narrators. Today I'm doing the same thing with three Flolights 500LED lights. But you can't light big areas with them, and you can't control the light as easily as you can fresnels. If you light with fluorescents, or LEDs, you're lighting with softlights. If you had a set of, say, Lowel DP lights with 500 watt lamps and diffusion gel clipped to the barn doors, it would be similar. (Although with the LEDs I have, they are not as soft as fluorescents and need to be diffused when in close.)
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Old February 27th, 2008, 12:56 PM   #3
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By my math, the fluorescents are twice as efficient using your figures: 55W producing 2900 lumens vs. 750W producing 20000 lumens (53 lm/W vs. 26.6 lm/W)

If you want to the know why this is possible, it is because tungstens use up a lot of energy to generate radiation beyond the visible spectrum (at the infrared side). That is why they get hot.
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Old February 27th, 2008, 09:02 PM   #4
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As Bill said, its a diffusion / soft light issue.

When someone says that something is "equivalent of an 800w tungsten" (or whatever), you should automatically fill in the word "softbox" (if they don't do it for you) after the tungsten to make the comparison valid. Also, I would say its very optimistic of Lowell to say that they are getting 26 lpw out of a tungsten bulb. The average is more in the 15 to 20 lpw range with many of the most common at 10 lpw.

In addition, once you put the tungsten bulb behind the diffusion material, no way are you getting 20,000 lumens.
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