A method for generating a beam of light that impinges on a target, wherein beam intensity remains substantially constant regardless of beam spot size. The method involves: providing a light source, a lens that can be moved to or between various positions, a slide having positions at which the lens may be supported, a target at which a beam is directed and a controller that communicates between an optical position feedback encoder and the light source; linking the encoder and the lens, the encoder sending a lens position signal to the controller, including an encoder translator circuit which communicates with a microprocessor that receives user inputs which characterize desired beam size at the target; generating a light source power signal to the light source so that electrical power delivered by the light source changes in response to the position of the lens.