1 electron = 1 photon?

Started Apr 12, 2013 | Discussions thread
OP Jack Hogan Veteran Member • Posts: 6,053
Re: Average QE without integer arithmetic

alanr0 wrote:

So I don't see anything special happening at unity gain.  With a few dozen electrons or more, electron statistics (shot noise) will dominate.  At lower signal levels, the 'electron counting' argument is only valid if ADC levels align precisely with the sensor black point for every pixel.  I agree that higher ADC gains will deliver diminishing returns from this point, but there is nothing magic about unit gain ISO.

Without digging deeper, I am happy to follow John Sheehy, who seems to prefer prefer measurement and sound analysis to vague arm-waving arguments about the way the world ought to work.

Excellent, convergence then

For 5500K black body radiation, energy is distributed more or less equally into bands 400-500, 500-600, 600-700 nm (give or take 10% or so, see table in Kaye & Laby, or image here).

Assume 48% QE for 555 nm light incident on each green sensor, in line with your analysis, and only a little better than the KAF 8300 data sheet.  The green filter width at 50% of maximum transmission is approximately 100 nm, so roughly 1/3 of the available light is captured (compared with monochromatic green light at 555 nm).

Yes, that's a nice way to approximate it.  The power being the same over the three bands would mean that we should have more photons in the Red band than in the Blue band.  And that's ok, because that would then allow similar colored emitters to produce the same relative output power, say, on a Monitor.


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