I know that wireless cyclo computers will not work with an HID but does anyone know if they interfere with heart rate monitors?

I have the L&M Li-Ion ARC HID. It did not interfere with my HRM, only with my Sigmasport BC800 wireless. I switched to a wired mount for my BC800.

HID don't always, or even usually, interfere with wireless cyclocomputers. My Light and Motion ARC Li-Ion works fine with my Cateye Micro wireless unless I installed them within about two inches of each other. I haven't tried a HRM, though.

No effect on my Polar HRM. Overheat power lines at one location is the only thing that has ever effected my HRM (interesting seeing your HRM suddenly jump up to 260 BPM).

If relocating the light relative to the other equipment does not cure the problem and you want to stay wireless try using the thinnest metallized mylar sticky tape you can find. Should act as a Faraday cage absorbing EMF from the switching transistors in the power supply of the lamp. Try shielding just the power supply first. Check www.alliedelec.com for a local supplier. Or tape aluminum foil around the EMF source. Geeky but simple.

Hmm... I have an L&M L-Ion ARC as well and it has rendered my SI90HR useless but I have not tried it with the strap nor have I tried moving the equipment. Not that big a deal since I only use the light on the commute and I know my stat's on that route but it would be nice. Thanks for the suggestions and the info.

Do you ground the foil too?

I do not know for sure. I would not bother grounding it. Cars are not grounded and still serve as Faraday cages. Try it with aluminum foil first.

Ok, your bloody idea doesn't work for crap.
How am I supposed to see where I'm going now?

LOL

Dude! The aluminum foil goes over YOUR head!

Shiny side out!