Can a UV sterilizer bulb replace your saltwater aquarium light?
No. A UV sterilizer bulb is a maintenance part that sits inside a sterilizer unit and is not meant to light the tank. You will still need a dedicated display light that has the right spectrum, intensity, and coverage for viewing and for any photosynthetic organisms you keep.
Can a freshwater LED be used on a saltwater aquarium?
Many fixtures are labeled for both saltwater and freshwater, and they can work well for fish-only tanks or simple displays. If you keep corals or other photosynthetic organisms, choose a marine-focused light that gives the appropriate spectrum, higher output, and coverage for your tank size and depth.