As mentioned under “photometric” (above), there are 2 different ways of measuring light. One is how a human observer sees light, and the other is how a machine would detect light if it wasn’t messed with. Radiometric deals with the measurements of light you take where you don’t care how a human would see it.
So, for example, any sort of infrared (IR) measurements are going to be radiometric, because humans can’t see IR light!
Most sensors, high-powered lasers where you’re melting metal, any other wavelengths outside the visible spectrum are usually measured with radiometric units. For those, you’ll be using radiant flux in Watts and radiant intensity in Watts per steradian.