Brake light vs fog light?

This is sort of Landy-related. At least, I'm using Land Rover parts

I'm planning to rig up a rear fog light on my motorbike to try and improve visibility in bad weather. My bike is effectively my 'normal' car so I ride it in all weathers. The plan is to use a spare Defender rear light (an indicator bulb with a red lens from a brake light, to be exact) mounted to the underside of the top box.

Is there any fundamental difference between the light output of a brake light compared to a 'proper' fog light? The bulb is the same, but not sure if there's any difference in how the lenses focus the light.

The lens pattern is different I'm fairly sure.
Won't a normal tratter fog light fit somewhere?

Flossie said:

Won't a normal tratter fog light fit somewhere?

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Probably would, but I don't have one of those handy. But I swapped some of the lights on my 90 a while back, and as it was easier to get a complete set, I've got a few of the round lights and lenses going surplus

The rules probably aren't written for bikes, but you may need to fit a warning light on your dash (or somewhere up front) to show it is switched on. An illuminating switch would do it without any extra work!

I went ahead and hooked this up on the bike. Happy with the result, particularly as it didn't cost me anything except a few surplus bits and pieces

Much brighter than the rather pathetic single tail light. I offset the light to the right side to help distinguish it from a brake light. Plus it lines up nicely with the indicator. Bring on the fog!