What is a good quantum efficiency?

Modern scientific CCDs reach 90% or higher at peak wavelength. Consumer CMOS sensors typically achieve 50-80%.

Does QE vary with wavelength?

Yes, significantly. QE peaks in the visible or near-infrared and drops in the blue and UV. Spectral QE curves are important for filter selection.

Read noise at short exposures and sky background shot noise at long exposures. Higher QE helps in all regimes.

Calculate the number of photoelectrons generated by a CCD sensor: electrons = photon_flux * area * QE * exposure_time.

Photon Flux

photons/m2/s

Pixel Area

Quantum Efficiency

Exposure Time

Photoelectrons per Pixel

6.75 e-

Shot Noise2.60 e-

Photoelectrons per Pixel vs Photon Flux

Quantum efficiency (QE) is the fraction of incoming photons that produce a detectable photoelectron in the sensor.

N_e = F * A * QE * t

*F* = photon flux (photons per m2 per second)

*A* = pixel area

*QE* = quantum efficiency (0 to 1)

*t* = exposure time

Shot noise follows a Poisson distribution: sigma = sqrt(N_e).

3.75 um pixels (A = 1.406e-11 m2), QE = 0.80, flux = 1e10 ph/m2/s, 60 s exposure.