As the current pulse travels through the tube, it ionizes the atoms, causing them to jump to higher energy-levels. Three types of particles are found within the arc plasma, consisting of electrons, positively ionized atoms, and neutral atoms. At any given time during the flash, the ionized atoms make up less than 1% of the plasma and produce all of the emitted light. As they recombine with their lost electrons they immediately drop back to a lower energy-state, releasing photons in the process. The methods of transferring energy occur in three separate ways, called "bound-bound," "free-bound," and "free-free" transitions.