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[1]

...the light falloff is bigger with CFL and LED lights than with Tungsten

I never understood that one. Where does it fall to, exactly?

[cgbier]

I don't know either. It just happens.

[Janke]

Light falloff = weaker light off-axis, i.e. good exposure in the middle of the frame, darker in edges and corners.

[cgbier]

You name a specific case. Light fall off means simply that emitted light gets lost over a distance, regardless of direction.

[cgbier]

But to answer MrMicah's question more constructively: there are a few dealers <cough> Lunchbox who name lumen values at specific distances for their lights. This gives you a good indicator.

You can peruse a mathematical formula that helps you to calculate the needed EV for a specific lumen value. Would have to dig that out, but I bet you can find it on Wikipedia.

[Janke]

light gets lost over a distance, regardless of direction.

Oh yes, that's the normal "inverse square law", light diminishes as the square of the distance - regardless of light type. I think it's a myth that it's different for CFLs...

[MrMicah]

Thank you gentlemen.

[1]

I think it's a myth that it's different for CFLs

Aye, that's what I meant. I don't understand how light emitted from a CFL or a LED could "fall off" differently than any other source.

I assume the "myth" started because the CFLs may have simply had a wider beam angle.

[Janke]

I assume the "myth" started because the CFLs may have simply had a wider beam angle.

Exactly - and they usually never measure up to the advertise "tungsten equivalent" wattage, either...

[cgbier]

It sounds like it is a myth, but it is true. The inverse square law is valid and true for point sources, which the CFL aren't. Therefore, a difference in light fall off. Try it out with a light meter.

[Dr. Benway]

Ask the potheads - their life is light.

https://mycotopia.net/forums/grassro...some-help.html

[Janke]

The inverse square law is valid and true for point sources

You can consider a CFL as an infinite number of (very) small point sources bunched together; so the inverse square law still applies... disregarding the small perturbation due to them not being in the exactly same spot, of course. This would be pretty insignificant at a distance of from a few feet onwards.

Even a reflector can't help, really. Only a coherent source of light (i.e. laser) that doesn't diverge, won't obey the iSQ law, as I understand it.

[Janke]

I did a little check, here's Wikipedia:

In photography and theatrical lighting, the inverse-square law is used to determine the "fall off" or the difference in illumination on a subject as it moves closer to or further from the light source. For quick approximations, it is enough to remember that doubling the distance reduces illumination to one quarter;[4] or similarly, to halve the illumination increase the distance by a factor of 1.4 (the square root of 2), and to double illumination, reduce the distance to 0.7 (square root of 1/2). When the illuminant is not a point source, the inverse square rule is often still a useful approximation; when the size of the light source is less than one-fifth of the distance to the subject, the calculation error is less than 1%.[5]

[cgbier]

The 1% holds true for Kinoflos. Pigtails lose more faster (I tried it out).

[Janke]

Pigtails lose more faster

Why would they disobey the laws of physics? Because they are swine??

[cgbier]

Yep!

[MrMicah]

Hmmm ... I think light, whatever its origin, would have constant physical properties, so I'd guess the inverse-square rule holds (within the parameters of our practical interest).

[cgbier]

It should, but if you have a light meter, test it out yourself. I'm close to throw away my pigtail kit and go back to the Arris.

[MrMicah]

But does the pigtail throw out the rated light from its origin?

Or are you doing a reading off a reflector at Y distance and then 2 x Y distance and noticing the reduction is more than y squared?

[cgbier]

The main issue is that it sends out most of the light to the side. I have a reflector inside the soft box that helps a bit to direct the light on a short distance, but when I go further away, there barely's any of the reflected light left. The diffuser in front of the box adds to the problem.

The only time a pigtail shines is when you put it inside a China Ball.

[cgbier]

Or are you doing a reading off a reflector at Y distance and then 2 x Y distance and noticing the reduction is more than y squared?

Yes.

[Halsu]

Yes.

Do you really get more than a two stop reduction in exposure every time you double the distance to the light? I'm pretty sure that is not true.

Inverse square dropoff is the absolute worst case scenario, where you have a point light source emitting equally to all directions in a completely black space.

If you change the size to something bigger than a point, you get less falloff (the bigger the light source in relation to the distance to subject, the less dropoff). If you use a lens / reflector to direct more of the light in a parallel fashion, you get less falloff (pinspots and laser pointers are an extreme example of this). If you operate in an environment that is not absolutely black, you get less falloff in practice due to environmental reflection.

As far as i can tell, there's no cases where you could get more than a inverse square dropoff in light intensity, except if you have i.e. strong dust or smoke in the air that would eat up the light.

[cgbier]

It's about 1/3 to 1/2 stop with the first doubling of distance I lose.

[Halsu]

It's about 1/3 to 1/2 stop with the first doubling of distance I lose.

That's roughly just one quarter of inverse square reduction...

[Janke]

I think he means in addition to the two-stop loss - right, CG?