How much light do modifiers absorb?

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.

Why do softboxes lose more light than umbrellas?

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.

How does modifier light loss affect my guide number?

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 35.

Is more diffusion always better?

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.

PhotoCalcs

Light Modifier Calculator — Light Loss Comparison

Compare light loss across different modifier types and calculate effective flash output.

Flash Power

Flash output before the modifier, as a % of full power (e.g. 100 = full, 50 = 1/2 power)

Modifier TypePick the modifier — each carries a typical stop-loss; choose Custom to enter your own

How We Calculate This

Light modifiers absorb or scatter light, reducing the effective flash output:

Output After Modifier

Output = flash power / 2^(stops loss)

Guide Number Reduction

GN multiplier = 1 / 2^(stops loss / 2)

GN uses the square root because guide number relates to the square root of illuminance (inverse-square law), not power directly. 1 stop of light loss halves the light, so it divides GN by √2 ≈ 1.41 — i.e. multiplies GN by 1/√2 ≈ 0.71.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.