The softness of the source is directly related to the surface area of the light emitter - and the distance that surface is from the object being lit.
When I pick a two lamp or a four lamp fluorescent fixture. I'm generally not looking for how MUCH light it puts out. tho obviously the more tubes, the more light.
I'm looking at the SHAPE of the light I want to throw at a subject.
Fluorescent lights are said to be SOFT because the tubes are relatively long compared to bulb style lamps.
When you put multiple tubes in an array, the height of the array comes closer and closer to matching the width of the array. Which means light will hit the object from more directions simultaneously.
So if I mount a 2 foot fluorescent tube vertically - positioned 3 feet from a person's head - I'd expect to get nice diffuse lighting up and down their face, but not as much wrap side to side as I would with a physically wider 4 bank array.
If I took the same 2-foot light and positioned it horizontally, I'd get nice side to side wrap, but much more fall off above and below the subject because the light emitting surface is not as tall.
In carefull lighting, the valued "softness" of a light can be lost if you don't use it properly. And a 2 bank fluroescent unit - being wide in one dimension and skinny in the other, will always be less "soft" on one axis.
Skinny lights are cool when used when skinny highlights are important - a good example is lighting something tall and slim like a wine bottle.
And used properly with people, they can create very interesting and dramatic shadows.
But a 2 bank fluorescnet would typically NOT be the first fixture I'd grab for lighting an interview unless I wanted to make it pretty moody, or the subject had an issue like a squat face or bad hair and I wanted to use the dimensional light falloff to de-emphasise features that a larger light array would reveal.
My 2 cents, anyway.
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