There is a lot of confusion about when you can and can't operate Daytime Running Lights (DRLs) on motorcycles in the UK (and EU). This isn't surprising because, for cars, the requirement is to have them switch off or dim when the headlights are used. But many motorcycles have dipped beam on if the engine is running. That presents a bit of a conundrum.

I've searched the net trying to find clear directions for motorcyclists operating DRLs and failed to find anything conclusive. But I did find a couple of useful extracts from the UK Department for Transport DRL Information Sheet...

"DRLs are necessarily bright to ensure they are visible in the daytime but not so bright that they will dazzle others. However they are too bright for night time use and are not intended to illuminate the road in the dark. If used at night they will cause dazzle and discomfort to others and so drivers should always switch to their position lamps or headlamps at night."

and...

"Ideally retro fitted DRLs should be installed such that they activate automatically when the engine starts and switch off when headlamps are turned on. If this is not the case then you must ensure that you manually turn DRLs off at night as they will cause dazzle and discomfort to others if used in low ambient lighting conditions."

The AA suggest that manually operated daytime running lights should be turned off at night to avoid dazzling other road users.

So the primary requirement, for operating DRLs, is they must not dazzle other road users at any time. Outside of this it seems to me that it's a case of common sense... Always fit a manual on-off switch and don't use them at night with dipped beam.