Low-light imaging: exposure time matters as much as brightness
Separate a bright still scene from useful evidence of moving subjects.
Updated
Principle and limits
Light collected depends on illumination, aperture, transmission and exposure time. Gain amplifies a signal and its noise; it does not add captured photons. Noise reduction may hide fine or moving detail. A quoted minimum illumination must include its measurement conditions; it cannot by itself prove usable moving faces or color fidelity at your site.
Worked example
At unchanged illumination and aperture, 1/25 s integrates light for ten times as long as 1/250 s. It can brighten a stationary scene but produces about ten times the motion smear for the same transverse motion. This simplified comparison ignores saturation and processing. Changing aperture or adding illumination changes the trade-off and must be tested.
Installation and acceptance
Review recordings of walking subjects and vehicles, not only a live still image. Record shutter, gain limits, frame rate, aperture and illumination. Check IR reflections from nearby surfaces, insects and rain; verify focus after day/night switching. Choose an exposure that preserves the required task, then evaluate noise and storage cost at that setting.
Scope of the reference
EMVA 1288 provides a framework for measuring camera and sensor characteristics. It does not establish this product’s minimum usable site illumination or night recognition performance; these require model evidence and recorded field tests.