In general terms, fluorescence occurs in two steps. First, an electron in your fluorescence marker is excited into a more active state by the laser. When the electron relaxes back to its ground state, it emits glowing fluorescent light. This figure demonstrates how fluorescence occurs in more detail than the animation, along with the correct terminology needed to ultimately select a laser and detector. Specifically, it can be seen in this illustration that a laser light generates a specific excitation wavelength that will excite the fluorescent marker electron to a higher energy level (indicated by the straight blue line). Note, only a specific excitationwavelength in nanometers (nm) will excite a given marker. Next, in step 2, the electron relaxes (indicated by the straight green line) to its original ground state, and the resulting fluorescent light is generated at a specific emission wavelength in nm. The specific emission wavelength of light in nm determines the color of the light. Finally, a specific detector can only read a specific emission wavelength of fluorescing light.