I have a Polar HRM and it seems to be really affected by my light. Has anyone had the same experience? Last night I wasn't even moving and I had a heart rate of 228bpm and it just wouldn't register any speed. Today its completely fine.

Any ideas how to 'shield' the HRM from the light?

From their webby

Why doesn’t my wireless computer or HRM work when my ARC HID light is on?
The ARC HID light produces a weak EMI (Electromagnetic Interference) that interferes with most wireless transmitters on cycle computers and heart rate monitors. You will need to either move the computer away from the light, approximately 12”, use a hard wired computer, or ride without your training device and just enjoy the night!

yes it's a standard problem with HRM's and high power lights. similar to the electricla interferance you can get from overhead power cables too. it's basicly Electromagnetic interferance.

nothing you can do about it other than to keep the two units apart. I presume you had both units on your handlebars. I found I needed to wear HRM on my wrist in order to keep them far enough apart that they don't interfer.

I hadn't realised the problem would be so bad. Its Seca700 and its a great light. The HRM is centrally mounted so apart from moving it to the other side of the handlebar where I normally have my emergency light I can't use.

Oh well I deserve it for riding my road bike!!

Thanks all.

Ah, this explains why I had a heartrate of 300 odd when I went past a marshall/first aid point on my first night lap at Relentless 24 last month. It must have been the huge lighting/generator system they had recently switched on.

I got interference in an XC race once before, first fireroad climb in a bit of a pack, I gather that was a case of too many HRMs in close proximity.

Train in the daytime?

Can he buy some shielding for the light?

700 lumens eh? I'm suprised you don't see everyone in xray mode when you ride Hopster! 😉

Riding tonight with the CR?

Wrap some copper wire or tinfoil round your HRM, I kid you not. Might dump enough EMR to stop it interfering so badly.

We had much the same with our TV aerial and Mrs ADH's monstrous hairdryer. One foil backed beach mat in the roof later, all the Mock the Week I can handle uninterupted.