Light Modifier Calculator — Light Loss Comparison

These are typical, approximate figures — real loss varies widely with modifier size, fabric and internal baffles. Reflective umbrellas lose roughly 0.5 stop. Shoot-through umbrellas lose about 1-2 stops. Softboxes lose around 2-3 stops, with larger boxes and octaboxes at the higher end because light travels further to the front diffusion panel. Adding a grid or extra diffusion adds another 0.5-1 stop. Beauty dishes lose less (around 1-2 stops with a diffusion sock; bare with the reflector they can even concentrate light). Large diffusion panels can lose 2.5-3 stops. The trade-off is always power for quality.

Softboxes pass light through diffusion material (typically 1-2 layers), which absorbs some light. The internal reflective surface also absorbs a small amount. Reflective umbrellas simply bounce light off a reflective surface with minimal loss. Shoot-through umbrellas lose more because the light passes through the fabric.

Guide number is reduced by the square root of the light loss factor. A 1-stop loss (50% light) reduces GN by factor 0.71 (√0.5). A 2-stop loss reduces GN by 0.5. So a GN 58 flash with a 1.5-stop softbox becomes effectively GN 58 x 0.59 = GN 34.

Not necessarily. More diffusion creates softer light but wastes more flash power. For small speedlights, heavy modifiers can leave insufficient power. Match your modifier to your flash power and working distance. Sometimes a reflective umbrella at closer range gives softer light than a large softbox far away.