The present invention provides a frontal light diffusing device comprising a non-circular core fiber section having a proximal end and a distal end, and a lens； wherein fiber core of the non-circular core section has a “top hat” core irradiance distribution and the frontal light diffusing device provides a “top hat” spatial irradiance distribution at a targeted location. The present invention further provides a frontal light diffusing device comprising an optical fiber and a collimation lens assembly wherein the collimation lens assembly includes a variable aperture that blocks portions of light outcoupled from the optical fiber thereby allowing only a central portion of the light to exit through the variable aperture resulting in a flat irradiance distribution.
