Biologists who want to learn how many photons they have in their experiment
An easy, step-by-step guide for measuring photons
It seems like a difficult question that would require sophisticated equipment and complex measurements to figure out. But it turns out you can get a pretty close estimate of how many photons are in a given pixel using some simple math and equipment you already have.
Cameras output image brightness information in grey values. In the literature, you sometimes see image intensity data expressed as “ADU’s” or “DN’s” (arbitrary digital units or digital numbers). The point here is that the grey values are, in fact, arbitrary. The good news is that it’s possible to back-calculate and know how many photons were detected. Here’s how to do it.
That’s it. Now you have the number of photons for each pixel. Of course there are many variables such as filters, optics, reflections, etc. that could move the numbers in one direction or another. But this method is accurate to within a few percentage points.
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