Lighting Intensity and Exposure Calculator
Calculate illuminance (lux), exposure value (EV), luminous intensity, and camera exposure settings using standard photometric and photographic formulas.
Illuminance & Exposure Calculator
Formulas Used
Illuminance (Inverse Square Law):
E = (I / d²) × cos(θ)
where E = illuminance (lux), I = luminous intensity (cd), d = distance (m), θ = angle of incidence
Exposure Value from Lux (ISO 2720):
EV = log₂(E × S / K)
where E = illuminance (lux), S = ISO speed, K = incident light meter calibration constant (≈ 12.5)
EV from Camera Settings:
EV = log₂(N² / t) − log₂(S / 100)
where N = f-number (aperture), t = shutter speed (seconds), S = ISO
Shutter Speed from EV, Aperture, ISO:
t = (N² × 100) / (2^EV × S)
where t = shutter speed (s), N = aperture f-number, S = ISO
Distance from Desired Lux:
d = √(I / E)
where d = distance (m), I = intensity (cd), E = desired illuminance (lux)
Assumptions & References
- Illuminance calculations assume a point source in free space with no obstructions or reflections.
- The incident light meter calibration constant K = 12.5 is used per ISO 2720 standard (common for Sekonic and most professional meters).
- EV is calculated at the specified ISO; EV 0 corresponds to 1 second at f/1.0 at ISO 100.
- Angle of incidence is measured from the normal (perpendicular) to the illuminated surface.
- Camera shutter speed is derived assuming the given aperture and ISO are fixed.
- Typical lux levels: Overcast day ~1,000 lux; Office lighting ~300–500 lux; Full sunlight ~100,000 lux; Moonlight ~1 lux.
- References: ISO 2720:1974 (General Purpose Photographic Exposure Meters), CIE S 017 (ILV: International Lighting Vocabulary), IESNA Lighting Handbook.