Dyonics Smith & Nephew 300XL Zenon Light Source

Dyonics Smith & Nephew 300XL Zenon Light Source has discoloring on front, aside from discoloring it is in good physical condition with minor scratches and scuffs (see pictures). Unit powers on and i can see light coming out of the opening but no way to test for functionality. We have 3 of this items in the same working order, the only difference between them is the discoloration. ALL QUESTIONS AND OFFERS WELCOME