Possible Light Interference with GPS?
A couple of months ago, around the time change, I got a new Garmin Edge 500 GPS and Baja Designs Stryker II light. The GPS I mount on my stem and the light goes on the bars next to the stem (with the extra wire wrapped a few times around the stem spacers). For the first half dozen or so rides I noticed my GPS data would sometimes be off both in mileage and track...to the point that I started to also carry my Garmin 305 in my Camelbak as a backup. I contacted Garmin about it and they recommended I do a satellite realignment, which I did. That seemed to fix things and I haven't had any trouble for the past couple of weeks.
Then last night I went for a ride and my Garmin 500 had a lot of trouble locating satellites. It took 10+ mins before it finally linked up. During the ride it was losing reception with the satellites and on the final hill back to my car I noticed my speed was showing 15-20 mph, when I know I was sub-10 mph. That got my thinking and I realized for the past couple of weeks I've been on vacation and only doing day rides. I decided to turn off my bar light and noticed that the speed reading seemed to drop back to normal and stabilize.
So is this just a coincidence or could the light be interfering with the GPS signal and/or internal electronics? I've got a couple of lights and two GPS I can do some testing with, but I figured I'd throw the question out here to see what the interwebs thought.