The incident photon excites the molecule into a virtual state.

These results indicate that absorption occurs for an incident photon.

On the quantum level, we picture this as incident photons all traveling in the forward direction and being scattered isotropically.

To force this alternative emission to occur, an incident photon must strike the fluorophore.

E is the energy of the incident photon.

However, there is no way to know that those emitted photons are the same as the incident photon.

Most lead collimators let less than 1% of incident photons through.

A state that cannot absorb an incident photon is called a dark state.

It is an interaction between the incident photon and the outermost electron.

A photomultiplier will produce a small current even without incident photons; this is called the dark current.