A compact, self-powered, selectively-mountable lighting unit (102) provides light directable by a user to an operation site in a confined space to enable the user to operate a tool therein. The lighting unit (102) is detachably mountable to, for example, a surgical instrument (100) so as to provide lighting of selected frequency range in adjustable focus ranging from substantially diffuse to tightly focused beam, at and about an operating distal end of the instrument (100) to facilitate accurate viewing thereof.