I found these very bright 1" diameter LED lights on Ebay They are currently GBP£1.29, which at today's exchange rate is US$1.62

So far I have fitted them to my utility hybrid and my personal trailer, and three of them will be going onto the rear of the tadpole trike I am presently building, and I will probably be fitting them on to any other complete bikes & trikes I may build in the future.

They have 3 modes; steady light, fast flash and slow flash. They can easily been seen out to 85 metres in all modes and they are waterproof .... I can vouch for that because here in the UK it is almost always very wet.

They have an anodized aluminium body of about 1" diameter and are available in 4 colours, with "O"ring seals between the sections and fix in place with a single M5 X 0.8 Set screw or with the supplied rubber band. I have used an M5X 0.8 A4 stainless steel button head hex set screw for permanent fixing onto my bike and trailer, and I will also use the same on the trike.