The Lighting Hierarchy
From best to worst for face matching: 1. Overcast outdoor daylight, diffuse, even, spectrally balanced, no shadows. 2. Open shade outdoors, reflected skylight, still diffuse. 3. Large window indoors, north or east facing, bright day. 4. Ring light, frontal, even, slight specular. 5. Softbox or bounce flash, diffuse artificial light. 6. Standard room lighting, usually workable if multiple sources. 7. Directional lamp alone, creates strong one-sided shadows. 8. Smartphone LED flash, harsh, flat, bleaches features. 9. Backlighting, avoid entirely.
The higher in this hierarchy your light source, the better your match quality will be.
Practical Setups for Common Environments
Indoors without dedicated lighting: sit facing a window rather than with the window behind you. Supplement with a lamp pointed at the ceiling to reduce shadows on the opposite side. The goal is multiple light sources or diffuse light, not a single point source.
Outdoors in direct sun: face away from the sun (stand so the sun is behind the camera, not behind you). Or wait for cloud cover or find open shade. Direct sun from the side creates dramatic shadows that are visually striking but poor for face recognition. Fully frontal direct sun causes squinting, which alters eye geometry.