Design allowances made to prevent or reduce the effects of high-energy radiation and high-energy bombardment, such as gamma radiation and neutron bombardment, which cause some optical fibers to depart from normal operating parameters, such as to lose transparency and thus increase attenuation. Note: Optical devices, such as light sources, lightemitting diodes (LEDs), lasers, and couplers also need to be hardened to prevent failure when exposed to high radiation levels. Synonym  fiber nuclear hardening. See also  attenuation,  coupler,  failure,  fiber optic coupler,  fiber optic,  nuclear hardening,  gamma radiation,  laser,  level,  light-emitting diode,  light source,  neutron bombardment resistance,  optical fiber,  parameter,  radiation,  transparency.