This invention deals with the broad general concept for focussing light. The light spectrum is digitized and inputted into a data processing unit in which it is compared to the actual spectrum of the light source stored in the system to determine the absorbance spectrum of the fluid. Power switches in both a power converter and power inverter are cooperatively controlled with dynamic dvdt control to reduce switching noise according to a profile specified by the controller. An elongate arm has a first end operably attached to the proximal portion of the tubular body and a second end providing an indicator establishing an axis aligned coaxially with the axis of the distal portion.