A portable high-intensity ultraviolet (UV-C) light gun is provided, the gun comprised of a high-intensity UV-C emitting light bulb mounted into a gun assembly. The gun assembly includes means for gathering and directing the high-intensity light emitted from the bulb and focusing the light into a beam that can be directed to a target. The gun assembly includes a light box that includes a bulb mount having electrical terminals for electrically connecting a UV bulb to a power source, and further includes a mirror for gathering and reflecting the emitted light towards an opening provided in the light box. One end of an elongated cylindrical hollow light tube is connected to the opening for channeling and focusing the emitted and reflected light from the light box toward the opposite open end of the tube. The tube can include a nozzle for further focusing and directing of the emitted light. Methods of using the gun to eradicate pathogens and other biological organisms are also provided.