Portrait & Boudoir Light Falloff Calculator
Start with your own readings. Calculate the change, verify a frame, and save what works.
Portrait & boudoir falloff
Plan face-to-chest, across-face and background illumination differences.
Choose the bright point and the darker point
Use this portrait and boudoir lighting calculator to plan a distance-based illumination difference between the face and chest, two points across a face, or the subject and background. The model shows a possible source position and its limits; it does not simulate a face or make light stop at a boundary.
- Choose a scene and measure the separation between the two subject points, or between the subject and backdrop. These are not camera-to-subject distances.
- Set a finite target in stops and the light angle. Inspect the source-to-face distance, height, second-point distance and practical-clearance warnings.
- Meter the two points with the same method. For close softboxes, beam edges or shadows, refine with actual readings, feathering and flags rather than trusting the point-source estimate.
For face and chest points one foot apart, an ideal point source directly above the face would need to be about 6.56 inches from the face for a three-stop distance-related drop at the chest. That close placement is usually a poor point-source assumption for a portrait softbox. The useful answer may be a controlled beam or flag, verified with readings.
Does three stops darker mean the chest will be black?
No. It means one eighth of the illumination from that light. Ambient, other lights, reflections, skin or clothing reflectance and camera rendering determine how dark it looks.
Can I make the light stop after one foot?
Light does not have an abrupt falloff boundary. Name two points and a brightness difference. A flag or restricted beam can block a path; distance falloff alone cannot create a hard cutoff.
Does half the light mean half the face is lit?
No. Half illumination is a one-stop difference. Lighting one side of a face is a shadow-placement problem involving direction, face shape and spill. Use the one-light recipe builder and a test frame.
Can the same frontal light expose the subject and backdrop identically?
In the stated aligned point-source geometry, a farther backdrop receives less illumination. For practical evenness, choose a small tolerance and adequate distance, or change geometry or add controlled fill. Different surface reflectance still affects appearance.
Learn the decision behind the setting.
By Dwayne of DNA Premium Portraits, Sacramento-area portrait photographer. See formulas, assumptions and equipment sources.
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