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| 18% grey 5 m wide cyclorama side lit actual measured percentage brightness at 1m intervals |
Are you placing lights in a studio thinking about f stops, angles, hardness and the resultant shadows but not about "Fall Off.?" Perhaps you never did "get" the inverse square law.
FACT: Light looses 75% of it's intensity in the first two meters from the source. Three meters out, it's down to 90%. Having lost most of it's punch in the first few meters it then looses very little as it travels further away from the lightsource.
A key to producing professional images, certainly in the genre fashion and beauty, is a clear understanding of light fall off and what causes it i.e. the inverse square law of light.
Fall off can range from zero to intense and is much more evident when the model is side lit.
Zero fall off light is termed "flat light." Much like you get on a overcast day. If we were shooting the face or mask of a model on an overcast day and turned the one side of the mask to the sun (well where we knew the sun should be) the light would be evenly distributed all over the mask. Meter the one cheek then the other, the readings would be the same. Zero fall off.
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| Model on an overcast day © Simon Stewart |
Rapid fall off is when we turn the mask to a light source - say a softbox - and the one side of the mask is well lit but the other side is quite dark. In other words the light that first strikes the one side of the mask has lost it's intensity rapidly just in the space of a few inches. The kicker here is that the closer the subject is placed to the light source the greater the fall off. The further away from the lightsource the flatter the light. The reason is that light looses it's intensity at a phenomenal rate in the first few critical meters and then eases off. So for maximum light fall off you need to work really close to the source definitey within 3 meters of a reflector or the diagonal of a square or rectangular soft box or the diameter of a circular one. i.e with a 60cm x 60cm softbox 85cm to the subject is the ideal distance for rapid fall off.
There are masses of theoretical diagrams out there showing this relationship between light source and intensity fall off but I shot the image above in the studio up against an 18% grey cyc 5 meters wide instead. The excercise was hardy scientific so the results were not quite as accurate as they should be but they are factual. It should give you a good idea of what I am rambling on about.
Put a model in the left hand zone and the light will be faling off by more than a half (75% in theory) over her body and face - high drama indeed. Now move her two meters away (adjust the apperture) and the fall of is minimal. The lighting ratio much closer, garment evenly lit, not much drama and typical catalogue look.
