a self contained , self - powered , bright , typically visible , light source in a strong case having a transparent dome is thrown or fired into position by police as a non - injurious agent of coercive intervention . light is emitted after a predetermined delay , typically ten seconds , from a unidirectional manual actuation , typically by act of pulling an insulating plastic strip from between electrical contacts within the case . once activated , the light source may not be readily deactivated , and will shine sufficiently brightly so as to be temporarily blinding to the direct view of any human who is close enough to the light source so as to touch it . a spent light source may be discarded but is commonly recycled by being recharged .