jamolnng

You are my hero.

http://i.imgur.com/r44Bswj.png ^{I know the actual quote, but humor me}

An actual answer is that particles and waves are just mathematical models that we use to describe the physics of light. A big goal in physics is trying to develop a model that unifies both. However we'll probably still be calling them particles and waves until the end of time because those models are generally the most useful unless you're doing super high energy or super low energy physics

For a large amount of photons, say coming from a LED, you can measure the photon flux (the amount of photons hitting a surface area) using semiconductor based detectors. These output an electric current based on the number of photons hitting it. Each photon essentialy knocks an electron loose and that adds to the current. From the current you can calculate the number of photons since current is electrons per second and each electron corresponds to a photon you get photons per second. These devices have some sort of efficiency less than 1 you have to take into effect tho but that's the general idea

For single photons, you can use single photon detectors like photomultipliers, Geiger counters, and others (more examples here: https://en.m.wikipedia.org/wiki/Photon_counting ). Photomultipliers and Geiger counters work by turning the single electron that is knocked loose by a photon into a waterfall of a bunch of electrons that can be detected as a pulse. There are other single photon detectors that use material properties such as measuring the resistivity of a material as it changes phases from superconducting to non-superconducting as a photon interacts with it but I'm not as familiar with those devices.

Source: PhD student who spends too much time on Reddit and not their research

Not op but a current PhD student. I always have had a love for physics since high school and got my BS in physics. I have always wanted to dig down and understand how pretty much everything, from computers to the universe works. I'm actually doing my PhD in physics but my focus is in optics and photonics. This field scratches that physics itch while also being a very applied field and let's me be hands on in the lab creating things so I get to understand what I make from the bottom up. It's a good sense of, in the words of EA, pride and accomplishment when you work hard on something, create it, it works, and you're the first person to do so