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If the eye can detect a single photon, it must mean that the triggering system in the human eye, which starts the electrical signal that carries the visual info
by runeks 10y ago
If the eye can detect a single photon, it must mean that the triggering system in the human eye, which starts the electrical signal that carries the visual information to the brain, needs less energy than a photon contains to be triggered. That's pretty amazing to me.
How many photons does a CCD chip need to change one pixel from pitch black? A billion? 1e20? I'm curious to know.
If we could figure out how this triggering system works, we could build amazing stuff. Probably more than really good camera chips.
- mtreis86 10y agoFrom https://en.wikipedia.org/wiki/Rod_cell https://en.wikipedia.org/wiki/Rod_cell "Activation of a single unit of rhodopsin, the photosensitive pigment in rods, can lead to a large reaction in the cell because the signal is amplified. Once activated, rhodopsin can activate hundreds of transducin molecules, each of which in turn activates a phosphodiesterase molecule, which can break down over a thousand cGMP molecules per second (Kandel et al. 2000). Thus, rods can have a large response to a small amount of light."
- danarlow 10y agoElectron multiplying CCD cameras can respond to single photons with > 90% quantum efficiency [1] -- that's better than rhodopsin. (I use one on a semi-daily basis.) To take advantage of that sensitivity you need to cool the sensor to -80°C so that thermal noise doesn't swamp your signal, but obviously you can't do that with your eyes. [1] http://www.andor.com/learning-academy/ccd,-emccd-and-iccd-comparisons-difference-between-the-sensors http://www.andor.com/learning-academy/ccd,-emccd-and-iccd-co...
- runeks 10y agoThat's pretty cool! Would you happen to know how many photons it takes to activate the average consumer CCD?