Taging Onto What Jeff Said......
If you have the teardrop style I would change them out in a heartbeat for something with better visibility. The Aqua Signal 25 or equal as Jeff mentioned would be my choice too.A couple years ago we were on our summer cruise and a couple in their Chrysler 25 sailboat (I think that's what it was) was T-boned by a fast aluminum sport fishing boat, twin high-horsepower outboards, also about 25 foot long. The fishing boat "ran up" on their coach roof and actually broke the boom, caved in the coach roof, deck, gunnel, and part of the hull. Fortunately the couple got out of the accident with only some minor injuries but their running lights may have been a factor in the collision.Their lights were the teardrop type, also faded lenses, and I'm sure were difficult to see. Given todays modern skyline with lights all over the place it is very difficult at best sometimes to see small running lights with this backdrop of lights. I'd highly recommend erring on the side of more candlepower and go with bigger running lights.It doesn't hurt to keep the lenses covered when the boat is at the dock on sitting on a trailer, either. The plastic lenses will stay chrisper much longer.When replacing them I'd also recommend using some silicone dielectric grease on the wire terminals (those little brass screws) and bulb contacts and marine grade heat shrink tubing on any butt-joint connectors.