Neutrophil granulocytes are the primary defense cells of blood against bacteria, fungi, parasites, or thrombi. Their main weapons and signals are reactive oxygen species (ROS) that release photons. The activation of the assembly of their NADPH-oxidase, the few specific triggers and many specific or unspecific primers are of great physiological and pathophysiological importance in inflammation and in hemostasis. The neutrophils generate different types of photons and they can "see" them. The 300-400 nm photons are the main signals and the photons of lowest wave length which seem to especially alert them in emergency. The present book presents research on the regulation of the neutrophil’s ROS generation by different photons, by singlet oxygen (the excited "pro-drug" of photons), by important proteins, or by modulators of the eicosanoid metabolism that should not favor the generation of systemically circulating micro-thrombi.