Understanding EV (Exposure Value)

EV is a combined measure of aperture and shutter speed that represents the amount of light reaching the sensor. It is calibrated to ISO 100. Common reference points: direct sunlight ≈ EV 15, overcast sky ≈ EV 12, bright office ≈ EV 9, candlelight ≈ EV 3.

EV reference

Lighting condition	Approx. EV (ISO 100)
Bright sunlight on snow / sand	16
Bright sunlight (average scene)	15
Hazy sunlight / light shadow	14
Cloudy bright (no shadows)	13
Overcast / heavy overcast	12
Open shade / golden hour	10–11
Indoors near a bright window	5–7
Typical home interior	3–5
Candlelit room	2
Dimly lit street at night	0–1

ISO / aperture / shutter speed triangle

For any given EV, there are many equivalent exposure combinations - this is the reciprocity law. Doubling the ISO, doubling the shutter speed, or opening the aperture by one stop each increases exposure by one EV. Photographers choose among combinations based on creative needs:

Fast shutter: freezes motion (sports, wildlife).
Wide aperture (low f-number): shallow depth of field (portrait blur).
Low ISO: least digital noise (studio, tripod work).

Lux vs. EV conversion

EV = log₂(Lux / 2.5)

Lux is the SI unit of illuminance (lumens per square meter). At EV 15 (bright sunlight), the scene illuminance is approximately 80,000 lux. At EV 5 (indoor window light), it is about 80 lux. The factor 2.5 assumes a scene reflectance of 18% (the photographic "middle grey" standard).

Limitations

This tool uses your webcam pixels as a proxy for scene luminance. Webcam auto-exposure and auto-white-balance circuits can affect readings significantly. Treat the values as rough estimates rather than calibrated measurements.

Privacy

Camera frames are analysed entirely within your browser using the Canvas API. No image data is transmitted.