T.D. Luckery: Evidence of health benefits and longer average life-span following low-dose irradiation should replace fear, “all radiation is harmful,” and “the perception of harm” as the basis for action in the 21st century. Hormesis is the excitation, or stimulation, by small doses of any agent in any system. Large doses inhibit. “Low dose” is defined as any dose between ambient levels of radiation and the threshold that marks the boundary between biopositive and bionegative effects. That threshold negates the “linear no threshold” (LNT) paradigm.