Why bother
If you can read the light in a photograph you admire, you can rebuild it. Three things carry nearly all the evidence: catchlights, shadows, highlights/rim lights.
1 · Catchlights — the light's fingerprint
- How many? One catchlight = one light. Two = a key plus a fill, reflector or second source.
- Where in the eye? Off to one side means the source is on that side. High and barely visible means the light is high relative to the face; if there's no top catchlight at all, the light was very high (or the chin very low).
- A catchlight only in the lower eye means light coming from below — a second source, or a reflector bouncing back up.
- Shape reveals the modifier: round octabox, rectangular softbox, long thin stripbox, irregular = reflector. A white reflector gives a dim, dull reflection; silver gives a brighter one.
- Size reveals distance: bigger catchlight = larger or closer source = softer light.
2 · Shadows — height and angle
- Vertical (length down the face): a long nose shadow reaching towards the lip = light placed high. A short nose shadow = the light is low.
- Horizontal (across the face): the longer the shadow to the side of the nose, the further the light is off-axis around the subject. Loop = short side shadow; Rembrandt = long side shadow.
- Depth of shadow tells you about fill. Very dark, detail-free shadows mean no fill — possibly negative fill (a black flag or dark surface pulling light out).
- Critical: patterns are set by the light relative to the face, not the camera. Turn the subject's head towards the light and Rembrandt becomes flat; you must move the light to get the pattern back.
3 · Rim lights and highlights
- Check the jawline and the hair — rim lights are often subtle, and there may be more than one.
- Quality: crisp, contrasty rim = zoom reflector, barn door or snoot. Softer, broad rim = strip softbox. Dim and soft = a bounce off a silver reflector, white wall or background.
- How far it wraps: a narrow rim means the light is angled further behind the subject; a rim that wraps around means the light has moved more to the side.
- Height: a low rim light misses the top of the shoulder; raise it and it climbs the neck into the hair. Very high, and it becomes a hair light.
The relative-size rule
The sun is enormous but far away, so it behaves like a tiny source — hard shadows. Put a shoot-through umbrella between sun and subject and the umbrella becomes the source: large, close, soft. Same physics indoors: a small softbox brought very close is softer than a big one far away.
Field routine
- Count the catchlights → how many sources.
- Read catchlight position → where the key is.
- Read catchlight shape and size → modifier and distance.
- Read nose-shadow length (down, then across) → height and angle.
- Read shadow depth → fill, or negative fill.
- Check jaw and hair → rim lights, their quality and height.
Consolidated from references: Lindsay Adler, Seeing the Light.